dizocilpine-maleate and Pain

Neuropathic pain is associated with abnormal tactile and thermal responses that may be extraterritorial to the injured nerve. Importantly, tactile allodynia and thermal hyperalgesia may involve separate pathways, since complete and partial spinal cord lesions have blocked allodynia, but not hyperalgesia, after spinal nerve ligation (SNL). Furthermore, lesions of the dorsal column, and lidocaine microinjected into dorsal column nuclei block only tactile allodynia. Conversely, thermal hyperalgesia, but not tactile allodynia was blocked by desensitization of C-fibers with resiniferotoxin. Therefore, it seems that tactile allodynia is likely to be mediated by large diameter A beta fibers, and not susceptible to modulation by spinal opioids, whereas hyperalgesia is mediated by unmyelinated C-fibers, and is sensitive to blockade by spinal opioids. Additionally, abnormal, spontaneous afferent drive in neuropathic pain may contribute to NMDA-mediated central sensitization by glutamate and by non-opioid actions of spinal dynorphin. Correspondingly, SNL elicited elevation in spinal dynorphin content in spinal segments at and adjacent to the zone of entry of the injured nerve along with signs of neuropathic pain. Antiserum to dynorphin A(1-17) or MK-801 given spinally blocked thermal hyperalgesia, but not tactile allodynia, after SNL, and also restored diminished morphine antinociception. Finally, afferent drive may induce descending facilitation from the rostroventromedial medulla (RVM). Blocking afferent drive with bupivicaine also restored lost potency of PAG morphine, as did CCK antagonists in the RVM. This observation is consistent with afferent drive activating descending facilitation from the RVM, and thus diminishing opioid activity, and may underlie the clinical observation of limited responsiveness of neuropathic pain to opioids.

Topics: Animals; Dizocilpine Maleate; Dynorphins; Humans; Hyperalgesia; Lidocaine; Morphine; Pain; Spinal Cord

It has been shown that an excitatory amino acid, such as glutamate and aspartate, plays an important role in the spinal nociceptive transmission. NMDA receptor is one of the receptors of excitatory amino acids. Glutamate is present in the terminals of small diameter primary afferent fibers, as well as in dorsal horn interneurons. It has been reported that NMDA receptor is not located postsynaptic to primary afferent input; rather it mediates excitation evoked by glutamate-releasing interneurons. Activation of chemosensitive afferents with chemical irritants generates a state of central sensitization in the spinal cord, and this hyperexcitability is blocked by NMDA antagonist. These data suggested that activation of chemosensitive afferents induces release of glutamate which activates NMDA receptor in dorsal horn interneurons, and that this NMDA receptor activation induces spinal sensitization. It has been suggested that this spinal sensitization plays an important role in the maintenance of neuropathic pain and hyperalgesia during inflammation. In the clinical trial, epidural administration of NMDA antagonist attenuated the level of allodynia in patients with postherpetic neuralgia. I think that spinal sensitization induced by NMDA receptor activation is the key mechanism to maintain neuropathic pain and hyperalgesia during inflammation.

Topics: Afferent Pathways; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Nociceptors; Pain; Rats; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Second Messenger Systems; Spinal Cord

The development of analgesic drugs is still a necessity due to the inefficiency of the current treatments for some pathological conditions and also due to the adverse effects produced by these drugs. The aim of this study was to deepen the pharmacological study of two new hybrids NSAIDs tetrahydropyran derivatives, regarding their antinociceptive effects on acute pain in mice. Male swiss mice were evaluated in the acetic acid-induced abdominal writhing, formalin, tail-flick, open-field, glutamate- and capsaicin-induced paw licking tests, and in vitro Cox inhibition assay, besides the acute toxicological evaluation. The compounds had an effect on the acetic acid-induced abdominal writhing, formalin (both phases), and tail-flick tests. In the study of the mechanism of action was observed reversion of the antinociceptive effect of the compounds from the previous administration of naloxone, L-NAME (L-nitro-arginine methyl ester), ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), glibenclamide, and nor-binaltorphimine, by the intrathecal and intraperitoneal routes. The prior administration of MK-801 suggests that the modulation of NMDA receptor contributes to the antinociceptive effect of compounds. In summary, hybrid compounds presented central antinociceptive effect, demonstrating participation of the NO-cGMP-K

Topics: Adenosine Triphosphate; Analgesics; Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Cyclic GMP; Cyclooxygenase Inhibitors; Dizocilpine Maleate; Formaldehyde; Glyburide; Humans; Male; Mice; Naloxone; Naltrexone; NG-Nitroarginine Methyl Ester; Pain; Pain Measurement; Potassium Channels; Prostaglandin-Endoperoxide Synthases; Receptors, N-Methyl-D-Aspartate; Signal Transduction

Dizocilpine is a highly selective and potent non-competitive antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor. It is well known that dizocilpine has different neuroprotective effects in animal models of pain, epilepsy and oedema during trauma. The search for alternative antiinflammatory drugs is ongoing. We investigated the anti-oedematous effects of dizocilpine and the probable mechanism of action in a rat model that mimics local and persistent inflammation without tissue injury or damage. Male Wistar rats were injected with 100 μL of 0.5% carrageenan to the plantar surface of the hind paw. Anti-oedematous activity was assessed in the carrageenan-induced paw inflammatory oedema test with a plethysmometer. To assess possible mechanisms of dizocilpine action, we examined the effects of the selective inhibitor of neuronal [N-ω-propyl-L-arginine hydrochloride (L-NPA)] and inducible [S-methylisothiourea (SMT)] nitric oxide synthase (NOS). Dizocilpine after systemic (0.0005, 0.005 and 0.02 mg/kg, subcutaneous (s.c.)), but not after local peripheral administration, reduced the paw inflammatory oedema. The effect is not dose dependent, and the highest decrease by about 47% at the time of maximally developed oedema was achieved with 0.005 mg/kg. Intraperitoneally (i.p.) administered L-NPA (0.5, 1 and 2 mg/kg) or SMT (0.005, 0.01 and 0.015 mg/kg) before dizocilpine abolished or reduced the anti-oedematous effect of dizocilpine by about 70-85%. An acute single dose of dizocilpine administered before inducing oedema systemically reduced the development of inflammatory oedema. The mechanism of the anti-oedematous effect includes, at least partially, an increase in nitric oxide (NO) production.

Topics: Animals; Anti-Inflammatory Agents; Arginine; Carrageenan; Dizocilpine Maleate; Edema; Inflammation; Isothiuronium; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Pain; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

μ-Opioid agonists are clinically effective analgesics, but also produce undesirable effects such as sedation and abuse potential that limit their clinical utility. Glutamatergic systems also modulate nociception and N-methyl D-aspartate (NMDA) receptor antagonists have been proposed as one useful adjunct to enhance the therapeutic effects and/or attenuate the undesirable effects of μ-opioid agonists. Whether NMDA antagonists enhance the antiallodynic effects of μ-agonists in preclinical models of thermal hypersensitivity (i.e. capsaicin-induced thermal allodynia) are unknown. The present study determined the behavioral effects of racemic ketamine, (+)-MK-801, (-)-nalbuphine, and (-)-oxycodone alone and in fixed proportion mixtures in assays of capsaicin-induced thermal allodynia and schedule-controlled responding in rhesus monkeys. Ketamine, nalbuphine, and oxycodone produced dose-dependent antiallodynia. MK-801 was inactive up to doses that produced undesirable effects. Ketamine, but not MK-801, enhanced the potency of μ-agonists to decrease rates of operant responding. Ketamine and nalbuphine interactions were additive in both procedures. Ketamine and oxycodone interactions were additive or subadditive depending on the mixture. Furthermore, oxycodone and MK-801 interactions were subadditive on antiallodynia and additive on rate suppression. These results do not support the broad clinical utility of NMDA receptor antagonists as adjuncts to μ-opioid agonists for thermal allodynic pain states.

Topics: Analgesics; Analgesics, Opioid; Animals; Conditioning, Operant; Dizocilpine Maleate; Dose-Response Relationship, Drug; Hyperalgesia; Ketamine; Macaca mulatta; Male; Nalbuphine; Oxycodone; Pain; Pain Measurement; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu; Reinforcement Schedule

The histamine H4 receptor (H4R) has attracted a lot of attention in terms of its role in antinociception. The N-Methyl-d-aspartic acid (NMDA) receptor is a well-characterized participant in pain pathways. However, it's influence on H4R signaling is poorly understood. Thus, in the present study we investigated the effect of a selective H4R antagonist JNJ7777120 (25mg/kg) and a NMDA receptor antagonist MK-801 (0.1-10μg) on nociceptive thresholds in a rat acute pain model.. The influence of intrathecally (it), intracerebroventricularly (icv) and intraplantarly (ipl) administered MK-801 co-injected with JNJ7777120 administered intraperitoneally (ip) was determined in the modified Randall-Selitto paw pressure, the tail flick and plantar tests.. Both ip JNJ7777120 as well as MK-801 delivered it and ipl increased nociceptive pain thresholds. It and ipl pretreatment with MK-801 additively augmented JNJ7777120 mechanical antinociception. A weaker effect was also observed after it co-administration with MK-801 and JNJ7777120 in the tail flick test. Intracerebroventricular MK-801 failed to produce any effect nor did ipl MK-801 in the plantar test.. The results show for the first time that the H4R and NMDA receptors play a significant role in antinociception in an acute non-inflammatory pain. Furthermore, the blockage of NMDA receptors at the peripheral and spinal, but not supraspinal sites produces a profound antinociceptive response upon simultaneous H4R antagonism. Thus, this study clearly demonstrates the relevance of NMDA and H4R receptors in the modulation of pain signals and that their role is not exclusively limited to their modulatory activity in inflammatory pain states.

Topics: Acute Pain; Analgesics; Animals; Dizocilpine Maleate; Histamine Antagonists; Indoles; Male; N-Methylaspartate; Pain; Pain Measurement; Piperazines; Rats; Rats, Wistar; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4

Phospho-ERK1/2 (pERK1/2) fluorescence-immunohistochemistry is specifically well suited to mirror neuronal activity in the pain pathway at the cellular level. This study employed this method to visualize neuronal activity in 3 rat CNS nuclei following an acute noxious stimulation. The rat hind paw was stimulated either by heat or by a sequence of mustard oil and heat. Two min after the thermal stimulation or after the combined mustard oil and thermal stimulation, there was a significant increase in cells showing pERK1/2 immunoreactivity in the supraoptic nucleus (SON), in the dorsal raphe nucleus (DRN), and in the locus coeruleus (LC). Pretreatment with the opioid analgesic morphine or the N-methyl-D-aspartate antagonist MK-801 markedly attenuated ERK1/2 phosphorylation. These findings support the concept that the SON, the DRN, and the LC are integrated into pain processing at the hypothalamic and brain stem level.

Topics: Analgesics, Opioid; Animals; Brain; Dizocilpine Maleate; Dorsal Raphe Nucleus; Hot Temperature; Immunohistochemistry; Locus Coeruleus; Pain; Phosphorylation; Rats; Rats, Sprague-Dawley; Supraoptic Nucleus

The most recently identified tachykinin, hemokinin-1, was cloned from mouse bone marrow. While several studies indicated that hemokinin-1 is involved in pain and inflammation, the physiological functions of hemokinin-1 are not fully understood. Our previous research demonstrated that the intrathecal (i.t.) administration of hemokinin-1 (0.00625-1.6 nmol) dose-dependently induced nociceptive behaviors, consisting of scratching, biting and licking in mice, which are very similar with the nociceptive behaviors induced by the i.t. administration of substance P. Low-dose (0.0125 nmol) hemokinin-1-induced nociceptive behavior was inhibited by a specific NK1 receptor antagonist; however, high-dose (0.1 nmol) hemokinin-1-induced nociceptive behavior was not affected. In the present study, we found that the nociceptive behaviors induced by hemokinin-1 (0.1 nmol) were inhibited by the i.t. co-administration of MK-801 or D-APV, which are NMDA receptor antagonists. Moreover, we measured glutamate in the extracellular fluid of the mouse spinal cord using microdialysis. The i.t. administration of hemokinin-1 produced a significant increase in glutamate in the spinal cord, which was significantly reduced by co-administration with NMDA receptor antagonists. These results suggest that hemokinin-1-induced nociceptive behaviors may be mediated by the NMDA receptor in the spinal cord.

Topics: 2-Amino-5-phosphonovalerate; Animals; Behavior, Animal; Dizocilpine Maleate; Glutamic Acid; Injections, Spinal; Male; Mice; Nociception; Pain; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Tachykinins

Pain is a significant public health concern, and current pharmacological treatments have problematic side effects and limited effectiveness. N-methyl-d-aspartate (NMDA) glutamate receptor antagonists have emerged as one class of candidate treatments for pain because of the significant contribution of glutamate signalling in nociceptive processing.. This study compared effects of the NMDA receptor antagonists ketamine and MK-801 in assays of pain-stimulated and pain-depressed behaviour in rats. The nonsteroidal anti-inflammatory drug ketoprofen was examined for comparison as a positive control. Intraperitoneal injection of dilute acid served as an acute visceral noxious stimulus to stimulate a stretching response or depress intracranial self-stimulation (ICSS) in male Sprague-Dawley rats.. Ketamine (1.0-10.0 mg/kg) blocked acid-stimulated stretching but failed to block acid-induced depression of ICSS, whereas MK-801 (0.01-0.1 mg/kg) blocked both acid-stimulated stretching and acid-induced depression of ICSS. These doses of ketamine and MK-801 did not alter control ICSS in the absence of the noxious stimulus; however, higher doses of ketamine (10 mg/kg) and MK-801 (0.32 mg/kg) depressed all behaviour. Ketoprofen (1.0 mg/kg) blocked both acid-induced stimulation of stretching and depression of ICSS without altering control ICSS.. These results support further consideration of NMDA receptor antagonists as analgesics; however, some NMDA receptor antagonists are more efficacious at attenuating pain-depressed behaviours.. NMDA receptor antagonists produce dissociable effects on pain-depressed behaviour. Provides evidence that pain-depressed behaviours should be considered and evaluated when determining the antinociceptive effects of NMDA receptor antagonists.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Ketamine; Male; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Self Stimulation

The ionotropic glutamate receptorantagonists include two types: MK-801, antagonist of N-methyl-D-asparticacid (NMDA) receptor, and NBQX, antagonist of non-NMDA receptor.The above-mentioned ionotropic antagonists can block the glutamate and its corresponding receptor binding to produce analgesic effect. The objective of this research was to study two antagonists in analgesic effect on rat behavior,as well as to investigate the down-regulation and up-regulation of cyclooxygenase-2 (COX-2) and Janus-activated kinase (Jak3) in collagen-induced arthritis (CIA) rat serum and tissue fluid after the application of these antagonists, that is, the effect on molecular biology.. This study used the ionotropic glutamate receptors as the target and established CIA rat model. Vivo studies were used to observe changes in behavior and molecular biology of the CIA rat.Behavioral assessment includedmechanical allodynia and joint swelling in the CIA rat,where themechanical allodynia was measured using the paw-withdrawal threshold (PWT) with VonFrey filaments according to the "Up-Down" method,and the drainage volume was used to assess joint swelling. Then the blood samples taken from the heart of the rat and the tissue homogenate were collected to detect the down-regulation and up-regulation of COX-2 and Jak3 in the serum and tissue fluid after the antagonists wereused.. Using MK-801, NBQX alone or using the combination of these two antagonists,these three methods all could alleviate pain(P<0.01).The analgesic effect lasted more than 24 h.Both antagonists reached the peak of analgesia at the end of 4 hours post-injection. NBQX had stronger analgesic effect than MK-801 (P<0.05).Whether alone or combined use of these two antagonists,could not change the CIA rats' swelling of the joint (P>0.05). MK-801 could decrease the expression of COX-2 (P<0.01).At the same time, NBQX did not have this effect (P>0.05). Using MK-801, NBQX alone or combination of these two antagonists could not affect the increased expression of Jak3 caused by the CIA (P>0.05).. MK-801 and NBQX could both alleviate pain, NBQX was much better than MK-801. Neither MK-801 nor NBQX had the effect on the swelling of the joint. NMDA receptor and COX-2 inflammatory pathways had certain interactions. For Jak3, it could not be found to have cross-function with ionotropic glutamate signaling pathways by this experiment.

Topics: Analgesics; Animals; Arthritis, Experimental; Cyclooxygenase 2; Dizocilpine Maleate; Edema; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Hyperalgesia; Janus Kinase 3; Male; Pain; Quinoxalines; Rats; Receptors, N-Methyl-D-Aspartate

Post-traumatic stress disorder (PTSD) is an anxiety disorder that occurs following an unexpected exposure to a severe psychological event. A history of a brief trauma is reported to affect a risk for future PTSD development; however, little is known about the mechanisms by which a previous trauma exposure drives the sensitivity to a late-coming trauma. Using a mouse PTSD model, we found that a prior foot shock enhances contextual fear conditioning. This shock-induced facilitation of fear conditioning (i.e., priming effect) persisted for 7 days and was prevented by MK801, an N-methyl-D-aspartate receptor antagonist. Other types of trauma, such as forced swimming or tail pinch, did not induce a priming effect on fear conditioning. Thus, a trauma is unlikely generalized to modify the sensitivity to other traumatic experiences. The behavioral procedure employed in this study may be a useful tool to elucidate the etiology of PTSD.

Topics: Animals; Anxiety; Conditioning, Classical; Dizocilpine Maleate; Electroshock; Excitatory Amino Acid Antagonists; Fear; Male; Mice; Mice, Inbred C57BL; Pain; Stress Disorders, Post-Traumatic; Stress, Psychological

Evidence corroborates the role of the anterior cingulate cortex (ACC) in the modulation of cognitive and emotional functions. Its involvement in the motivational-affective component of pain has been widely investigated using different methods to elucidate the specific role of different neurotransmitter systems. We used the peripheral noxious stimulus-induced vocalization algesimetric test to verify glutamatergic and GABAergic neurotransmission in the guinea pig ACC. Microinjection of homocysteic acid (DLH; 30 nmol) in the left guinea pig ACC increased the amplitude of vocalizations (pronociception) compared to controls injected with saline. Moreover, microinjection of MK-801 (3.6 nmol), an NMDA receptor antagonist, did not alter the amplitude of vocalizations, but its microinjection prior to DLH prevented the increase in vocalizations induced by this drug. Regarding the GABAergic system, blockade of GABAA receptors with bicuculline (1 nmol) increased the amplitude of vocalizations, while three different doses of the GABAA agonist muscimol (0.5, 1 and 2 nmol) did not influence nociceptive vocalization responses. Finally, a combination of MK-801 (3.6 nmol) and muscimol (1 nmol) reduced the amplitude of vocalizations (antinociception), suggesting that a combination of glutamate and GABA in the ACC modulates the expression of affective-motivational pain response. We suggest that activation of NMDA receptors or blockade of GABAergic neurotransmission promotes pronociception and that the antinociceptive effect of muscimol depends on the blockade of NMDA receptors.

Topics: Animals; Bicuculline; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Agents; GABA Agents; gamma-Aminobutyric Acid; Glutamic Acid; Guinea Pigs; Gyrus Cinguli; Homocysteine; Male; Microinjections; Muscimol; Pain; Time Factors; Vocalization, Animal

As previously reported, magnesium ions (Mg(2+)) administered in relatively low doses markedly potentiated opioid analgesia in neuropathic pain, in which the effectiveness of opioids is limited. Considering that Mg(2+) behaves like an N-methyl-D-aspartate receptor antagonist, the effect of this ion on the analgesic action of morphine was compared with that of MK-801. Acute pain was evoked by mechanical or thermal stimuli, whereas neuropathic hyperalgesia was induced by streptozotocin (STZ) administration. Magnesium sulphate (40 mg/kg i.p.) or MK-801 (0.05 mg/kg s.c.) administered alone did not modify the nociceptive threshold to acute stimuli or the streptozotocin hyperalgesia but significantly augmented the analgesic action of morphine (5 mg/kg i.p.). Furthermore, if these drugs (i.e. magnesium sulphate and MK-801) were applied concomitantly, a clear additive effect on the analgesic action of morphine occurred in both models of pain. Possible explanations of these observations are discussed.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Excitatory Amino Acid Antagonists; Hyperalgesia; Magnesium Sulfate; Male; Morphine; Neuralgia; Pain; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Streptozocin

The N-methyl-D-aspartate (NMDA) receptor, an ionotropic glutamate receptor, may play a significant role in the development and maintenance of an inflammatory pain. Activation of NMDA receptors may cause nitric oxide (NO) release through activation of NO synthase (NOS). MK-801, a noncompetitive NMDA receptor antagonist is commonly used as a neuropharmacological tool. The interaction between MK-801 and NOS in the inflammatory pain has not been evaluated before. We investigated whether MK-801 affects inflammatory pain and whether NOS modulates the effect of MK-801. Carrageenan-induced hyperalgesia was evaluated by measuring the withdrawal response to mechanical stimuli, using an electronic version of the von Frey anesthesiometer in Wistar rats. MK-801 given subcutaneously (0.5-20 μg/kg) or intraplantarly (0.1 and 0.15 μg/paw) significantly reduced mechanical hyperalgesia. Intraplantarly given MK-801 exerted a local antihyperalgesic effect, because when applied to the contralateral side it did not reduce mechanical sensitivity in the ipsilateral side. N-nitro-L-arginine methyl ester hydrochloride (5 and 10 mg/kg), a non-selective NOS inhibitor, significantly reduced the effects of MK-801. N-ω-Propyl-L-arginine hydrochloride (0.5-2 mg/kg), a selective inhibitor of neuronal NOS, increased the antihyperalgesic effect of MK-801, whereas S-methylisothiourea (5-15 μg/kg), a selective inhibitor of inducible NOS, lowered the antihyperalgesic effect of MK-801. Importantly, each NOS inhibitor given alone did not affect carrageenan-induced hyperalgesia. In conclusion, MK-801 is effective against inflammatory pain and its antihyperalgesic effect is modulated in a different ways by NOS, being enhanced by a neuronal NOS inhibitor but reduced by an inducible NOS inhibitor.

Topics: Animals; Arginine; Carrageenan; Dizocilpine Maleate; Hyperalgesia; Inflammation; Isothiuronium; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Pain; Pain Threshold; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Memantine is a N-methyl-D-aspartic acid receptor (NMDAR) channel blocker that binds to dizocilpine sites and appears well tolerated during chronic use. Published studies suggest NMDAR antagonists prevent development of tolerance to effects of morphine by blocking NMDAR hyperactivation.. We sought to compare effects of memantine to those of the more frequently studied dizocilpine and to evaluate memantine as a potential adjunct to modify tolerance to mu-opioid receptor agonists.. Sprague-Dawley rats were trained to discriminate morphine (3.2 mg/kg) and saline under fixed ratio 15 schedules of food delivery. Potency and maximal stimulus or rate-altering effects of cumulative doses of morphine were examined 30 min after pretreatment with dizocilpine (0.032-0.1 mg/kg) or memantine (5-10 mg/kg) and after chronic treatment with combinations of dizocilpine or memantine and morphine, 10 mg/kg twice daily, for 6 to 14 days. Effects of dizocilpine or memantine on morphine antinociception were examined in a 55 °C water tail-withdrawal assay with drug treatments parallel to those in discrimination studies.. Acutely, memantine attenuated while dizocilpine potentiated the stimulus and antinociceptive effects of morphine. Neither chronic dizocilpine nor memantine blocked tolerance to the stimulus effects of morphine. In contrast, combined treatment with dizocilpine (0.1 mg/kg) blocked tolerance to antinociceptive effects of lower (0.1~3.2 mg/kg) but not higher doses of morphine, whereas memantine did not block tolerance.. Memantine and dizocilpine interacted differently with morphine, possibly due to different NMDAR binding profiles. The lack of memantine-induced changes in morphine tolerance suggests that memantine may not be a useful adjunct in chronic pain management.

Topics: Analgesics, Opioid; Animals; Discrimination Learning; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Drug Tolerance; Excitatory Amino Acid Antagonists; Male; Memantine; Morphine; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu; Reinforcement Schedule

Excessive N-Methyl-d-aspartate receptor (NMDAR)-dependent production of nitric oxide (NO) is involved in the development and maintenance of chronic pain states, and is mediated by postsynaptic density protein-95 (PSD-95). By binding to both the NMDAR and neuronal NO synthase (nNOS), PSD-95 mediates a specific coupling between NMDAR activation and NO production. NMDAR antagonism shows anti-nociceptive action in humans and animal models of chronic pain but is associated with severe disturbances of cognitive and motor functions. An alternative approach to modulate the NMDAR-related activity is to perturb the NMDAR/PSD-95/nNOS complex by targeting PSD-95, thereby decreasing NO production without interfering with the NMDAR ion channel function. Here, we compared the effects of a dimeric PSD-95 inhibitor, UCCB01-125, and the NMDAR antagonist, MK-801, on mechanical hypersensitivity in the complete Freund's adjuvant (CFA) model of inflammatory pain. To examine side-effect profiles we also compared the effects of UCCB01-125 and MK-801 in tests of attention, long-term memory, and motor performance. When administered concurrently with CFA, both MK-801 and UCCB01-125 prevented the development of CFA-induced mechanical hypersensitivity 1 and 24 h after treatment. Moreover, UCCB01-125 was found to reverse CFA-induced hypersensitivity when administered 24 h after CFA treatment, an effect lasting for at least 3 days. At the dose reducing hypersensitivity, MK-801 disrupted attention, long-term memory, and motor performance. By contrast, even high doses of UCCB01-125 were devoid of side-effects in these tests. The data suggest that PSD-95 inhibition is a feasible strategy to prevent both development and maintenance of chronic inflammatory pain, while avoiding NMDAR antagonism-related side-effects.

Topics: Animals; Cognition; Dimerization; Disks Large Homolog 4 Protein; Dizocilpine Maleate; Enzyme Inhibitors; Female; Guanylate Kinases; Inflammation; Inflammation Mediators; Membrane Proteins; Mice; Motor Skills; Oligopeptides; Pain; Polyethylene Glycols; Receptors, N-Methyl-D-Aspartate

Knockout mice lacking the adenosine A(2A) receptor are less sensitive to nociceptive stimuli, and this may be due to the presence of pronociceptive A(2A) receptors on sensory nerves. In support of this hypothesis, we have recently shown that in A(2A) receptor knockout mice there are marked reductions in the changes of two markers of spinal cord neuronal activity, [(3)H]MK801 binding to NMDA receptors and uptake of [(14)C]-2-deoxyglucose, in response to formalin injection. We now report that following a more prolonged inflammatory stimulus, consisting of intraplantar injections of PGE(2) and paw pressure, there was in contrast an increase in [(3)H]MK801 binding and [(14)C]-2-deoxyglucose uptake in the spinal cords of the A(2A) receptor knockout mice which was much greater than in the wild-type mice. This increase suggests that when there is a pronounced inflammatory component to the stimulus, loss of inhibitory A(2A) receptors on inflammatory cells outweighs the loss of pronociceptive A(2A) receptors on peripheral nerves so that overall there is an increase in nociceptive signalling. This implies that although A(2A) antagonists have antinociceptive effects they may have only limited use as analgesics in chronic inflammatory pain.

Topics: Animals; Antimetabolites; Autoradiography; Deoxyglucose; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Inflammation; Mice; Mice, Knockout; Pain; Receptor, Adenosine A2A; Spinal Cord

Glutamic acid (Glu) participates in pain modulation of the central nervous system. The CA3 region of the hippocampal formation has been suggested to be involved in nociceptive perception. However, it is unknown whether Glu could modulate the electrical activities of pain-related neurons in the hippocampal CA3 region. The present study aimed to determine the effects of Glu and its receptor antagonist MK-801 in the pain-evoked response of both pain-excited neurons (PENs) and pain-inhibited neurons (PINs) in the hippocampal CA3 region of normal rats. We used a train of electric impulses applied to the sciatic nerve as noxious stimulation. The electrical activities of either PENs or PINs in the hippocampal CA3 region were recorded by a glass microelectrode. The results revealed that intra-CA3 region microinjection of Glu (0.5 μg/1 μl) increased the evoked firing frequency and shortened the firing latency of PEN, while decreased the evoked firing frequency and prolonged the inhibitory duration of PIN in the hippocampal CA3 region of rat evoked by the noxious stimulation. Intra-CA3 region administration of MK-801 (0.25 μg/1 μl) produced the opposite response. These results suggest that Glu and its receptors in hippocampal CA3 region are involved in the modulation of nociceptive information transmission by affecting the electric activities of PENs and PINs.

Topics: Animals; CA3 Region, Hippocampal; Dizocilpine Maleate; Electric Stimulation; Electrophysiological Phenomena; Excitatory Amino Acid Antagonists; Extracellular Space; Glutamic Acid; Microelectrodes; Neurons; Pain; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Stereotaxic Techniques

A series of experiments using technologies of gene mutation and silencing as well as chemical biology have demonstrated that spinal D-amino acid oxidase (DAAO) contributes to the development of central sensitization-mediated chronic pain and might be a potential molecular target for the treatment of chronic pain. DAAO inhibitors are now under clinical investigations for the management of chronic neuropathic pain. This study examined the interactions between morphine and the DAAO inhibitor CBIO (5-chloro-benzo[d]isoxazol-3-ol) in pain and analgesia tolerance mainly in the formalin test. Given subcutaneously CBIO acutely interacted with morphine in analgesia in an additive manner both in the acute nociception settings (the formalin acute phase nociception, hot-plate test and tail immersion test) and in formalin-induced tonic pain. Bi-daily exposure of CBIO given subcutaneously for 7 days did not produce self-tolerance to analgesia or cross-tolerance to morphine whereas 7-day subcutaneous morphine induced self-tolerance to analgesia but not cross-tolerance to CBIO. More importantly, subcutaneous co-administrations or even single dose of CBIO completely prevented or reversed morphine tolerance to analgesia (exhibited by a single dose or a dose-response curve of morphine) in both formalin-induced acute phase nociception and tonic phase pain. These results, for the first time, identified DAAO as an efficacious molecule mediating morphine tolerance, in addition to clarifying the complex interactions between morphine and DAAO inhibitors probed by CBIO, and provided a pharmacological basis for DAAO inhibitors in combination with morphine to clinically manage pain.

Topics: Analgesics, Opioid; Animals; D-Amino-Acid Oxidase; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Tolerance; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Injections, Spinal; Injections, Subcutaneous; Isoxazoles; Male; Mice; Morphine; N-Methylaspartate; Pain; Pain Measurement; Reaction Time; Receptors, N-Methyl-D-Aspartate

The involvement of spinal glial cells in the nociceptive behaviors induced by 1600 pmol of histamine was determined in mice. Histamine injected intrathecally (i.t.) produced nociceptive behaviors, consisting of scratching, biting and licking. The nociceptive behaviors induced by histamine were significantly suppressed by i.t. pretreatment with the glial cell inhibitor DL-fluorocitric acid or minocycline. In Western blot analysis using lumber spinal cords, i.t. treatment with histamine increased the phosphorylation of the NR1 subunit of N-methyl-D-aspartate (NMDA) receptors. The increased phosphorylation of the NR1 subunit of NMDA receptors by histamine was abolished by i.t. pretreatment with DL-fluorocitric acid or minocycline. We have previously reported that the nociceptive behaviors induced by 1600 pmol of histamine were significantly suppressed by the i.t. co-administration of (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5,10-imine (MK-801), an ion channel blocker of NMDA receptors, or agmatine, an antagonist for the polyamine recognition site on the NR1 subunit of NMDA receptors. In the present study, the increased phosphorylation of the NR1 subunit of NMDA receptors by histamine was also abolished by i.t. co-administration of agmatine or MK-801. The present results suggest that histamine at 1600 pmol elicits nociceptive behaviors by stimulating the polyamine recognition site on the NR1 subunit of NMDA receptors on spinal glial cells.

Topics: Agmatine; Animals; Behavior, Animal; Blotting, Western; Dizocilpine Maleate; Dose-Response Relationship, Drug; Histamine; Injections, Spinal; Male; Mice; Neuroglia; Pain; Pain Measurement; Phosphorylation; Receptors, N-Methyl-D-Aspartate; Spinal Cord

The long-lasting post-surgical changes in nociceptive thresholds in mice, indicative of latent pain sensitization, were studied. The contribution of kappa opioid and N-methyl-d-aspartate (NMDA) receptors was assessed by the administration of nor-binaltorphimine or MK-801; dynorphin levels in the spinal cord were also determined. Animals underwent a plantar incision and/or a subcutaneous infusion of remifentanil (80μg/kg), and mechanical thresholds (von Frey) were evaluated at different times. On day 21, after complete recovery of mechanical thresholds and healing of the wound, one of the following drugs was administered subcutaneously: (-)-naloxone (1mg/kg), (+)-naloxone (1mg/kg), naloxone-methiodide (3mg/kg), or nor-binaltorphimine (5mg/kg). Another group received subcutaneous MK-801 (0.15mg/kg) before nor-binaltorphimine administration. Dynorphin on day 21 was determined in the spinal cord by immunoassay. In mice receiving remifentanil during surgery, the administration of (-)-naloxone or nor-binaltorphimine induced significant hyperalgesia even 5months after manipulation. Nociceptive thresholds remained unaltered after (+)-naloxone or naloxone-methiodide. On day 21 after manipulation, the administration of MK-801 prevented nor-binaltorphimine-induced hyperalgesia. No changes in dynorphin levels were observed before or after opioid antagonist administration. In conclusion, surgery produced latent pain sensitization evidenced by opioid antagonist-precipitated hyperalgesia. The effect was stereospecific, centrally originated, and mediated by kappa opioid receptors. The blockade of nor-binaltorphimine-induced hyperalgesia by MK-801, suggests that NMDA receptors are also involved. Our results show for the first time that surgery induces latent, long-lasting changes in the processing of nociceptive information that can be induced by non-nociceptive stimuli such as the administration of opioid antagonists.

Topics: Animals; Dizocilpine Maleate; Dynorphins; Hyperalgesia; Male; Mice; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Pain Threshold; Piperidines; Postoperative Complications; Reaction Time; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, kappa; Remifentanil; Spinal Cord

This study examined the synergistic antinociceptive effects associated with signaling pathway proteins of the spinal cord in a complete Freund's adjuvant (CFA)-induced pain model when electroacupuncture (EA) and a N-methyl-D-aspartate receptor (NMDAR) antagonist were administered in combination. EA stimulation (2 Hz, 1 mA) was needle-delivered for 20 min once daily at acupoints corresponding to Zusanli and Sanyinjiao with intrathecal injection of the NMDAR antagonist dizocilpine (MK801). Thermal sensitivity of the hindpaw induced by CFA was strongly inhibited by dizocilpine injection and EA stimulation. Co-treatment with EA and dizocilpine showed a synergistic antinociceptive effect against inflammatory pain. On day two of the experiment, we examined the phosphorylation of the NMDAR NR2B subunit, of the extracellular signal-regulated kinase (ERK), p38 and of the cAMP response element-binding protein (CREB) in the ipsilateral dorsal horn of L4-5 segments by Western blot analysis. Phosphorylation of the NMDAR NR2B subunit induced by CFA was markedly inhibited by co-treatment with dizocilpine and EA, but not by dizocilpine or EA treatment alone. CFA-induced phosphorylation of the ERK was inhibited by both dizocilpine and EA, but that of p38 was inhibited by EA only. CFA-induced phosphorylation of CREB was inhibited by dizocilpine, but did not show marked changes. Immunohistochemical analyses confirmed that there was a significant difference in the NMDAR NR2B subunit and ERK phosphorylation. It is possible that the combined treatment with EA and the NMDAR antagonist dizocilpine resulted in synergistic antinociceptive effects in an inflammatory pain model via the inactivation of both the NMDAR NR2B subunit and ERK of the spinal cord.

Topics: Animals; Blotting, Western; Cyclic AMP Response Element-Binding Protein; Dizocilpine Maleate; Electroacupuncture; Extracellular Signal-Regulated MAP Kinases; Freund's Adjuvant; Immunohistochemistry; Male; p38 Mitogen-Activated Protein Kinases; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Signal Transduction

We have previously demonstrated that parathyroid hormone 2 (PTH2) receptors are expressed in dorsal root ganglion (DRG) neurons and that its endogenous agonist tuberoinfundibular peptide of 39 residues (TIP39) causes nociceptive paw flexor responses after intraplantar administration. Here we found that the PTH2 receptor is selectively localized on myelinated A-, but not unmyelinated C-fibers using immunohistochemical labeling, based on PTH2 receptor expression on antibody N52-positive medium/large-sized DRG neurons, but not on TRPV1, substance P, P2X(3) receptor or isolectin B4-binding protein-positive small-sized DRG neurons. Pharmacological studies showed that TIP39-induced nociceptive responses were mediated by activation of G(s) and cAMP-dependent protein kinase. We also found that nociceptive responses induced by TIP39- or the cAMP analog 8-bromo-cAMP were significantly greater following partial sciatic nerve injury induced neuropathic pain, without changes in PTH2 receptor expression. Together these data suggest that activation of PTH2 receptors stimulates nociceptive A-fiber through G(s)-cAMP-dependent protein kinase signaling, and this pathway has elevated sensitization following nerve injury.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Behavior, Animal; Capsaicin; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Ganglia, Spinal; Gene Expression Regulation; Glutamic Acid; Male; Mice; Mice, Inbred C57BL; Nerve Fibers, Myelinated; Neurons; Neuropeptides; Pain; Pain Measurement; Piperidines; Receptor, Parathyroid Hormone, Type 2; Reflex; Sciatica; Signal Transduction; Time Factors; TRPV Cation Channels

Zanthoxylum rhoifolium Lam. (Rutaceae) is locally known as "mamica de cadela", and its bark is popularly used for toothache and earache. The objective of this study was to investigate the antinociceptive effect of the ethanolic extract from this species' stem bark (EtOH), its fractions of partition (hexane-HEX, ethyl acetate-AcOEt, aqueous-AQ) and lupeol (a triterpene obtained from HEX) in models of acute pain.. Male and female Swiss mice (25-35 g, n=6-12 animals/group) were used to assess acute toxicity and nociception (Animal Ethics Committee/UFPI, No. 09/2008). Acute toxicity was studied up to 2 g/kg p.o. of EtOH. In the formalin test (2%, 20 microL/paw), the licking time of the stimulated paw was quantified during the first 5 min (first phase) and at 15-30 min (second phase), 1h after oral treatment with EtOH, HEX, AcOEt or saline, and 30 min after use of morphine-MOR (5 mg/kg i.p.). The same response evoked by capsaicin (2 microg/20 microL/paw) was quantified during 5 min, after administration of EtOH, HEX, AcOEt, AQ, saline and MOR. The licking time of the paw that was stimulated with glutamate (10 micromol/20 microL) was measured (15 min) after treatment with EtOH, HEX, AcOEt, AQ, lupeol, saline or MK801 (0.03 mg/kg, i.p.). Mice were submitted to the rota-rod task and open-field test in order to assess any non-specific muscle-relaxant or sedative effects of EtOH (250 mg/kg p.o.) and HEX (500 mg/kg p.o.).. The animals did not exhibit any acute toxicity to EtOH (up to 2 g/kg p.o.), so it was not possible to calculate the LD50. EtOH, HEX and AcOEt (62.5-250 mg/kg) produced a significant antinociceptive effect in the formalin and capsaicin tests. However, AQ was ineffective. EtOH, HEX, AcOEt and lupeol reduced the glutamate-evoked nociceptive response, but AQ had no effect. EtOH and HEX did not alter the locomotion of animals in the open-field or rota-rod tests, which suggest a lack of a central depressant effect.. The results confirm the popular use of Zanthoxylum rhoifolium as an analgesic, and contribute to the pharmacological knowledge of this species because it was shown that EtOH and its less polar partition fractions (HEX, AcOEt) have an antinociceptive effect in models of chemical nociception, and that lupeol appears to be one of the constituents responsible for this effect.

Topics: Analgesics; Animals; Behavior, Animal; Capsaicin; Disease Models, Animal; Dizocilpine Maleate; Ethanol; Female; Formaldehyde; Glutamic Acid; Locomotion; Male; Mice; Morphine; Pain; Pentacyclic Triterpenes; Phytotherapy; Plant Bark; Plant Extracts; Plant Stems; Zanthoxylum

Dizocilpine maleate (MK-801) causes the blockage of the glutamic acid (Glu) receptors in the central nervous system that are involved in pain transmission. However, the mechanism of action of MK-801 in pain-related neurons is not clear, and it is still unknown whether Glu is involved in the modulation of this processing. This study examines the effect of MK-801, Glu on the pain-evoked response of pain-excitation neurons (PENs) and pain-inhibition neurons (PINs) in the nucleus accumbens (NAc) of rats. The trains of electric impulses applied to the sciatic nerve were used as noxious stimulation. The electrical activities of PENs or PINs in NAc were recorded by a glass microelectrode. Our results revealed that the lateral ventricle injection of Glu increased the discharged frequency and shortened the discharged latency of PEN, and decreased the discharged frequency and prolonged the discharged inhibitory duration (ID) of PIN in NAc of rats evoked by the noxious stimulation, while intra-NAc administration of MK-801 produced the opposite response. On the basis of above findings we can deduce that Glu, MK-801 and N-methyl-D-aspartate (NMDA) receptor are involved in the modulation of nociceptive information transmission in NAc.

Topics: Analgesics; Animals; Dizocilpine Maleate; Glutamic Acid; Male; Neurons; Nucleus Accumbens; Pain; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Mice lacking the adenosine A(2A) receptor are less sensitive to nociceptive stimuli, and A(2A) receptor antagonists have antinociceptive effects. We have previously shown a marked reduction in the behavioural responses to formalin injection in A(2A) receptor knockout mice. This may be due to the presence of pronociceptive A(2A) receptors on sensory nerves, and if so spinal cords from A(2A) receptor knockout mice may have altered neurochemical responses to a nociceptive stimulus. We tested this hypothesis by studying two parameters known to change with spinal cord activity, NMDA glutamate receptor binding and [(14)C]-2-deoxyglucose uptake, following intraplantar formalin injection in wild-type and A(2A) receptor knockout mice. In naïve untreated A(2A) knockout mice [(14)C]-2-deoxyglucose uptake in all regions of the spinal cord was significantly lower compared to the wild-type, similar to the reduced NMDA receptor binding that we have previously observed. Following formalin treatment, there was an decrease in [(3)H]-MK801 binding to NMDA receptors and an increase in [(14)C]-2-deoxyglucose uptake in the spinal cords of wild-type mice, and these changes were significantly reduced in the A(2A) knockout mice. In addition to altered behavioural responses, there are therefore corresponding reductions in spinal cord neurochemical changes induced by formalin in mice lacking adenosine A(2A) receptors. These observations support the hypothesis that activation of A(2A) receptors enhances nociceptive input into the spinal cord and suggests a possible role for A(2A) antagonists as analgesics.

Topics: Animals; Deoxyglucose; Dizocilpine Maleate; Gene Deletion; Glucose; Male; Mice; Mice, Knockout; Pain; Pain Measurement; Radioligand Assay; Receptor, Adenosine A2A; Receptors, N-Methyl-D-Aspartate; Spinal Cord

1. The aim of the present study was to investigate the role of redox modulation during the peripheral nociceptive transmission in vivo. The nociceptive response was evaluated by the amount of time that mice spent licking the footpad injected with glutamate (20 micromol/paw). Thiol groups in footpad tissue were quantified using a colourimetric reaction with 5,5'-dithio-bis-2-nitrobenzoic acid (DTNB). 2. When coadministered with glutamate, the thiol alkylating agent iodoacetate (200 nmol/paw) caused significant antinociception in footpad tissue, in parallel with a decrease in free thiol groups. Treatment with the reducing agent dithiothreitol (200 nmol/paw) 5 min before glutamate and iodoacetate prevented the antinociception and thiol loss caused by iodoacetate. Injection of 100 nmol/paw ebselen (2-phenyl-1,2-benzisoselenazol-3[2H]-one), an in vitro redox modulator of the N-methyl-d-aspartate (NMDA) receptor, also prevented iodoacetate-induced antinociception. However, ebselen did not prevent thiol loss in the footpad. Dithiothreitol and ebselen had a synergic nociceptive effect with glutamate. 3. Alone, ebselen (100 nmol/paw) exhibited a pronociceptive effect. The nociception induced by ebselen was blocked by glutathione depletion induced by buthionine-sulphoximine (BSO; 2.5 micromol/paw). In addition, ebselen-induced nociception was prevented by 75 +/- 2% following injection of 5 nmol/paw MK-801 (an NMDA receptor antagonist). The nitric oxide synthase inhibitor N(G)-nitro-l-arginine (250 nmol/paw) had no effect on the nociception produced by ebselen. 4. In conclusion, the present paper reports on the effect of redox modulation on the glutamatergic system during peripheral nociceptive transmission in vivo. Antinociception was directly correlated with the availability of thiol groups, whereas the pronociceptive response of the reducing agents likely occurs via positive modulation of the NMDA receptor.

Topics: Alkylating Agents; Analgesics; Animals; Azoles; Behavior, Animal; Buthionine Sulfoximine; Disease Models, Animal; Dithiothreitol; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Female; Glutamate-Cysteine Ligase; Glutamic Acid; Glutathione; Iodoacetates; Isoindoles; Mice; Organoselenium Compounds; Oxidation-Reduction; Pain; Receptors, N-Methyl-D-Aspartate; Reducing Agents; Signal Transduction; Sulfhydryl Compounds

Cyclooxygenases-2 (COX-2) in the spinal dorsal horn is up-regulated and plays an important role in pain and hyperalgesia induced by nociceptive stimulation. The mechanisms involved in the up-regulation of spinal COX-2 during nociceptive stimulation are yet not well understood. Because the important role of NMDA and its receptor in transmission of nociceptive information in the spinal cord, activation of the spinal NMDA receptor might contribute to the up-regulation of spinal COX-2 expression. The present study was undertaken to demonstrate the above hypothesis by observing changes of COX-2 expression in the spinal dorsal horn in rats subjected to formalin test and intrathecal administration of NMDA, a selective NMDA receptor agonist, in conditions with or without presence of MK-801, an antagonist of NMDA receptor, using methods of Western blotting, reverse transcription polymerase chain reaction and immunohistochemistry. The results showed that intrathecal injection of MK-801, a noncompetitive antagonist of NMDA receptor, significantly suppressed the up-regulation of the COX-2 expression and characteristic pain behavior responses evoked in formalin test. Whereas, intrathecal injection of NMDA significantly up-regulated the expression of COX-2 in the spinal dorsal horn in a time course corresponding to that of nociceptive behavioral responses elicited by the intrathecal NMDA administration. In addition, the up-regulation of the COX-2 expression induced by the intrathecal NMDA was dose-dependent and blocked by prior administration of MK-801. These findings proved that activation of NMDA receptor is associated with the up-regulation of COX-2 expression in the spinal dorsal horn during nociceptive stimulation in rats.

Topics: Animals; Blotting, Western; Cyclooxygenase 2; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Formaldehyde; Hot Temperature; Hyperalgesia; Immunohistochemistry; Injections, Spinal; Pain; Pain Measurement; Physical Stimulation; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, N-Methyl-D-Aspartate; Reverse Transcriptase Polymerase Chain Reaction; RNA; Up-Regulation

Although mu-receptor opioids are clinically important analgesics, they can also paradoxically cause hyperalgesia independently of opioid receptor activity, presumably via the action of neuroexcitatory glucoronide metabolites. However, it is unknown whether the commonly used mu-receptor opioid analgesic fentanyl, which is not subject to glucuronidation, can also induce hyperalgesia independently of opioid receptor activity. Thus, here we examined whether fentanyl increases nociception on the tail-withdrawal test in CD-1 mice concurrently treated with the opioid receptor antagonist naltrexone or in opioid receptor triple knock-out mice lacking mu, delta, and kappa opioid receptors. For both groups, an acute fentanyl bolus dose (0.25mg/kg, s.c.) and continuous fentanyl infusion (cumulative daily dose: 10mg/kg) did not cause analgesia at any time. Instead, fentanyl significantly decreased withdrawal latencies relative to pre-drug values for the next 15-60 min and for six days, respectively. MK-801 blocked and reversed hyperalgesia caused by the acute injection and continuous infusion of fentanyl, respectively, in naltrexone-treated CD-1 mice, indicating the contribution of NMDA receptors to fentanyl hyperalgesia. These data show that the synthetic opioid fentanyl causes hyperalgesia independently of prior or concurrent opioid receptor activity or analgesia. Since the biotransformation of fentanyl does not yield any known pronociceptive metabolites, these data challenge assumptions regarding the role of neuroexcitatory metabolites in opioid-induced hyperalgesia.

Topics: Analysis of Variance; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Fentanyl; Hot Temperature; Hyperalgesia; Male; Mice; Mice, Knockout; Naltrexone; Narcotic Antagonists; Narcotics; Pain; Pain Measurement; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Time Factors

The periaqueductal gray (PAG) plays an important role in morphine antinociception and tolerance. Co-localization of mu-opioid and NMDA receptors on dendrites in the PAG suggests that glutamate may modulate morphine antinociception. Moreover, the involvement of glutamate in spinally mediated tolerance to morphine suggests that glutamate receptors may contribute to PAG mediated tolerance. These hypotheses were tested by microinjecting glutamate receptor antagonists and morphine into the ventrolateral PAG (vPAG) of the rat. Microinjection of the non-specific glutamate receptor antagonist kynurenic acid or the NMDA receptor antagonist MK-801 into the vPAG did not affect nociception. However, co-administration of these antagonists with morphine into the vPAG enhanced the acute antinociceptive effects of morphine as measured by a leftward shift in the morphine dose-response curves. Repeated microinjections of morphine into the vPAG caused a rightward shift in the dose-response curve for antinociception whether the glutamate receptor antagonists kynurenic acid or MK-801 were co-administered or not. The lack of effect of microinjecting glutamate receptor antagonists into the vPAG indicates that tonic glutamate release in the PAG does not contribute to nociceptive tone. That these antagonists enhance morphine antinociception indicates that endogenous glutamate counteracts the antinociceptive effect of morphine in the vPAG. However, this compensatory glutamate release does not contribute to tolerance to the antinociceptive effects of microinjecting morphine into the vPAG. Previous research showing that glutamate contributes to spinal mechanisms of tolerance indicate that different tolerance mechanisms are engaged in the vPAG and spinal cord.

Topics: Analgesia; Analgesics, Opioid; Analysis of Variance; Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Drug Tolerance; Excitatory Amino Acid Antagonists; Glutamic Acid; Hot Temperature; Kynurenic Acid; Male; Microinjections; Morphine; Pain; Pain Measurement; Periaqueductal Gray; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, Opioid, mu; Staining and Labeling

To test the hypothesis that peripheral N-methyl-D-aspartate (NMDA) receptors play a role in pain induced by experimental tooth movement.. Male Sprague-Dawley rats weighing between 200 g and 300 g were used in this study. Expression of NMDA receptors subunit 1 (NMDAR1) in the mandibular portion of the trigeminal ganglion (TG) was determined by Western blotting 4 hours and 1, 2, 3, 5, 7, and 14 days after tooth movement. Changes in the time taken by the rats on nocifensive behavior then effects of NMDA receptor antagonist MK-801 and force magnitude on these changes in behavior and NMDAR1 expression were evaluated.. Experimental tooth movement led to a statistically significant increase in NMDAR1 expression at protein level from day 1 to 7 after force application initiating tooth movement. Time spent on nocifensive behavior dramatically increased from day 1 to 7. The rhythm in NMDAR1 expression in the TG and behavioral activities correlated well with the initial orthodontic pain responses. The magnitude of the nocifensive behavior and NMDAR1 expression were both force magnitude dependent and could be reduced by peripheral NMDA receptor antagonist MK-801.. The hypothesis is accepted. Peripheral NMDA receptors are modulated by experimental tooth movement and involved in the development of tooth movement pain.

Topics: Animals; Dental Stress Analysis; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Grooming; Male; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Tooth Movement Techniques; Trigeminal Ganglion

To study the effect of intrathecal injection of MK-801, a NMDA receptor antagonist, on the NOS activity and NO content of hippocampus in rat during the process of formalin-induced inflammatory pain as well as the pain behavior of rat.. The degree of pain was determined by observing the time of licking and biting the injected paw. NOS expression in the hippocampus was determined by using NADPH-d histochemical staining. NO content of hippocampus was determined by assaying NO3; and NO2.. Subcutaneous injection of formalin elicited a characteristic pain behavioural response consisting of licking and biting the injected paw, etc. Intrathecal injection of MK-801 could shorten obviously the time of licking and biting representing pain behavioural response in phase 2. It is suggested that intrathecal injection of MK-801 could block the pain behavioural response induced by formalin (P < 0.05). The number and staining degree of NADPH-d positive neurons in formalin group significantly increased at 12 h after the formalin injection in CA1, CA2-3 and DG of hippocampus compared with control group as well as NO content, however, the number and staining degree of NADPH-d positive neurons in formalin + MK-801 group significantly decreased in contrast to those of formalin 12 h group as well as the NO content (P < 0.01).. Intrathecal injection of NMDA receptor antagonist MK-801 could inhibit the NOS activity and NO production in hippocampus of rat, which showed the increase of hippocampal NO production was mainly induced by the peripheral nociceptive information input.

Topics: Animals; Dizocilpine Maleate; Formaldehyde; Hippocampus; Inflammation; Injections, Spinal; Male; Nitric Oxide; Nitric Oxide Synthase Type I; Pain; Random Allocation; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

In animal studies of nociception, females are often more sensitive to painful stimuli, whereas males are often more sensitive to analgesia induced by mu-agonists. Sex differences are found even at birth, and in adulthood are likely caused, at least in part, by differences in levels of gonadal hormones. In this report, we investigate nociception and analgesia in neonatal mice and assess the contribution of the direct action of sex chromosome genes in hotplate and tail withdrawal tests. We used the 4 core genotypes mouse model, in which gonadal sex is independent of the complement of sex chromosomes (XX vs XY). Mice were tested at baseline and then injected with mu-opioid agonist morphine (10 mg/kg) or with the kappa-opioid agonist U50,488H (U50, 12.5 mg/kg) with or without the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (0.1 mg/kg). On the day of birth, XX mice showed faster baseline latencies than XY in tail withdrawal, irrespective of their gonadal type. Gonadal males showed greater effects of morphine than gonadal females in the hotplate test, irrespective of their sex chromosome complement. U50 and morphine were effective analgesics in both tests, but MK-801 did not block the U50 effect. The results suggest that sex chromosome complement and gonadal secretions both contribute to sex differences in nociception and analgesia by the day of birth.. Sex differences in pain may stem not only from the action of gonadal hormones on pain circuits but from the sex-specific action of X and Y genes. Identification of sex chromosome genes causing sex differences could contribute to better pain therapy in females and males.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesia; Analgesics; Analgesics, Non-Narcotic; Analgesics, Opioid; Analysis of Variance; Animals; Animals, Newborn; Behavior, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Injections, Subcutaneous; Male; Mice; Mice, Knockout; Morphine; Pain; Pain Measurement; Pain Threshold; Sex Characteristics; Sex Chromosomes; Sex Determination Processes; Sex Factors

Dorsal horn N-methyl-D-aspartate (NMDA) receptors contribute significantly to spinal nociceptive processing through an effect postsynaptic to non-primary glutamatergic axons, and perhaps presynaptic to the primary afferent terminals. The present study sought to examine the regulatory effects of NMDA receptors on primary afferent release of substance P (SP), as measured by neurokinin 1 receptor (NK1r) internalization in the spinal dorsal horn of rats. The effects of intrathecal NMDA alone or in combination with D-serine (a glycine site agonist) were initially examined on basal levels of NK1r internalization. NMDA alone or when co-administered with D-serine failed to induce NK1r internalization, whereas activation of spinal TRPV1 receptors by capsaicin resulted in a notable NK1r internalization. To determine whether NMDA receptor activation could potentiate NK1r internalization or pain behavior induced by a peripheral noxious stimulus, intrathecal NMDA was given prior to an intraplantar injection of formalin. NMDA did not alter the formalin-induced NK1r internalization nor did it enhance the formalin paw flinching behavior. To further characterize the effects of presynaptic NMDA receptors, the NMDA antagonists DL-2-amino-5-phosphonopentanoic acid (AP-5) and MK-801 were intrathecally administered to assess their regulatory effects on formalin-induced NK1r internalization and pain behavior. AP-5 had no effect on formalin-induced NK1r internalization, whereas MK-801 produced only a modest reduction. Both antagonists, however, reduced the formalin paw flinching behavior. In subsequent in vitro experiments, perfusion of NMDA in spinal cord slice preparations did not evoke basal release of SP or calcitonin gene-related peptide (CGRP). Likewise, perfusion of NMDA did not enhance capsaicin-evoked release of the two peptides. These results suggest that presynaptic NMDA receptors in the spinal cord play little if any role on the primary afferent release of SP.

Topics: Animals; Calcitonin Gene-Related Peptide; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Image Processing, Computer-Assisted; Male; Microscopy, Confocal; N-Methylaspartate; Neurons, Afferent; Pain; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Neurokinin-1; Substance P

In this study, the animal model of hypertonic saline (HS) infusion protocol was developed and utilized to test the hypothesis that HS causes peripheral release of glutamate, and that blockade of peripheral NMDA receptors significantly reduces HS-induced nocifensive behavior and central neuronal activation. Nocifensive behavior and c-fos immunoreactivity, as a marker of central neuronal activation, were assessed from the animals that received intramuscular HS infusion with and without the NMDA receptor antagonist, MK-801. HS infusion (20 microl/min for 10 min) in the rat masseter produced prolonged nocifensive hindpaw shaking responses that peaked in the first minute and gradually diminished over the infusion period. The HS induced nocifensive behavior was dose-dependently attenuated by MK-801 pretreatments (0.3 mg/kg and 0.1 mg/kg), but not by vehicle pretreatment (isotonic saline; ISO), in the masseter muscle. HS infusion produced a significant number of Fos positive neurons in the ispsilateral subnucleus caudalis (Vc). Subsequent immunohistochemical studies showed that peripheral MK-801 pretreatment effectively reduced the HS induced neuronal activation in the Vc. These results provide compelling evidence that HS-induced muscle nociception is mediated, in part, by peripheral release of glutamate, and that blockade of peripheral glutamate receptors may provide effective means of preventing central neuronal activation.

Topics: Animals; Biomarkers; Brain Stem; Data Interpretation, Statistical; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glucose Solution, Hypertonic; Immunohistochemistry; Injections, Intramuscular; Male; Masseter Muscle; Muscular Diseases; Neurons; Pain; Peripheral Nervous System; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Trigeminal Nuclei

The aim of the study was to investigate the possible role of MK-801, an NMDA antagonist, in analgesia induced by rilmenidine, an imidazoline (I(1)) agonist, in mice in the formalin test.. 25 microl of formalin 2.5% was injected into the dorsal surface of the right hind paw of the mouse. Pain response was scored after formalin injection for a period of 50 min. A weighted average of nociceptive score, ranging from 0 to 3, was calculated. The mean +/-SEM of scores between 0-5 and 15-40 min after formalin injection was presented.. The study showed that rilmenidine (1.25, 2.5 and 5 mg/kg, i.p.) produced analgesia dose-dependently (p<0.001) in formalin test. In addition, the results demonstrated that efaroxan (0.1 and 1 mg/kg, i.p.) could reduce the antinociceptive effect of rilmenidine (2.5 mg/kg, i.p.) (p<0.01) in animals, however, yohimbine (0.1 and 0.2 mg/kg, i.p.) could not block the analgesia induced by rilmenidine (2.5 mg/kg, i.p.) (p>0.05). On the other hand, MK-801 (0.05 mg/kg, i.p.) reduced the pain related behaviors in mice (p>0.05). Moreover, our findings demonstrated that MK-801 (0.01 mg/kg, i.p.) could potentiate the analgesic effect of rilmenidine (1.25 mg/kg, i.p.) significantly (p<0.01).. The present study suggests that imidazoline (I(1)) receptors play an important role in mediating the antinociception induced by rilmenidine in formalin test. Furthermore, it may be concluded that there is an interaction between NMDA receptors and imidazoline (I(1)) binding sites.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Analgesics; Animals; Benzofurans; Binding Sites; Binding, Competitive; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Synergism; Excitatory Amino Acid Antagonists; Imidazoles; Imidazoline Receptors; Male; Mice; Nervous System; Neurons, Afferent; Nociceptors; Oxazoles; Pain; Pain Measurement; Receptors, Drug; Receptors, N-Methyl-D-Aspartate; Rilmenidine; Yohimbine

Acute cholestasis is associated with increased activity of the endogenous opioid system that results to changes including analgesia. N-methyl-d-aspartate (NMDA) receptors are involved in the nociceptive pathway and play a major role in the development of morphine induced analgesia. The magnesium acts as a non-competitive NMDA receptor antagonist by blocking the NMDA receptor channel. Considering the reported antinociceptive effect of magnesium sulfate as a NMDA receptor antagonist and the existence of close functional links between NMDA receptor antagonists and magnesium with the opioid system, we studied the effect of acute and chronic administration of MK-801 as a NMDA antagonist and magnesium sulfate on modulation of nociception in an experimental model of elevated endogenous opioid tone, acute cholestasis, using the tail-flick paradigm. Cholestasis was induced by ligation of the main bile duct using two ligatures and then transsection of the duct at the midpoint between them. A significant increase (P<0.001) in nociception threshold was observed in bile duct ligated rats compared to unoperated and sham-operated animals. In acute treatment, MK-801 (0.1 mg/kg, b.i.d), but not magnesium (150 mg/kg magnesium sulfate, i.e. 30 mg/kg of Mg(+2), i.p., b.i.d.) increased antinociception in cholestatic rats compared to saline treated cholestatics (P<0.05). In chronic treatment, administration of MK-801 or magnesium sulfate for 7 consecutive days, increased tail-flick latency (P<0.05, P<0.01) in cholestatic animals compared to saline treated cholestatics. These data showed that NMDA receptor pathway is involved in modulation of cholestasis-induced antinociception in rats and that repeated dosages of magnesium sulfate similar to MK-801 is able to modulate nociception in cholestasis.

Topics: Analysis of Variance; Animals; Bile Ducts; Cholestasis; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Ligation; Magnesium; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

The nucleus cuneiformis (CnF), located just ventrolateral to the periaqueductal gray, is part of the descending pain modulatory system. Neurons in the CnF project to medullary nucleus raphe magnus (NRM), which plays an important role on pain modulation. In this study, we investigated the effect of microinjection of the non-competitive NMDA receptor antagonist MK-801, the competitive NMDA receptor antagonist AP-7, and the kainate/AMPA receptor antagonist DNQX, alone or in combination with morphine into the nucleus cuneiformis on morphine-induced analgesia to understand the role of glutamatergic receptors in the modulating activity of morphine. Antinociception was assessed with the tail-flick test. Morphine (10, 20, 40 microg in 0.5 microl saline) had an antinociceptive effect, increasing tail-flick latency in a dose-dependent manner. Microinjection of MK-801 (10 microg/0.5 microl saline) and AP7 (3 microg/0.5 microl saline) prior to morphine microinjection (10 microg/0.5 microl saline) attenuated the antinociceptive effects of morphine, whereas DNQX (0.5 microg/0.5 microl saline) showed a partial antinociceptive effect and potentiated the analgesic effect of morphine. These results indicated that the NMDA receptor partially potentiates the antinociceptive effect of morphine. Our results suggest that NMDA but not non-NMDA receptors are involved in the antinociception produced by morphine in the CnF. The non-NMDA receptors in this area may have a facilitatory effect on nociceptive transmission. The fact that morphine's effect was potentiated by NMDA receptor suggests that projection neurons within the CnF are under tonic, glutamatergic input and when the influence of this input is blocked, the descending inhibitory system is inactivated.

Topics: 2-Amino-5-phosphonovalerate; Analgesics, Opioid; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Male; Microinjections; Morphine; Nociceptors; Pain; Quinoxalines; Rats; Rats, Inbred Strains; Reaction Time; Receptors, AMPA; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Tegmentum Mesencephali

Neonates respond to noxious stimuli at or before birth, but the organization of nociceptive systems changes well into postnatal life. It is unknown how nociceptive information is processed in the immature animal and, specifically, whether noxious stimulation is transmitted by glutamatergic circuits, known to play an important role in nociception in the adult. Both N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are found within the neonatal spinal cord, but in immature form, and when they become involved in pain processing in vivo is not known.. The objective was to determine the age-related changes in the involvement of spinal NMDA and AMPA receptors in formalin-induced nociception during early life. Because the formalin test provides a measure of immediate nociceptive responding (first phase) and of peripheral and central sensitization (second phase), a second aim was to determine if there is specificity of the effects to either phase.. NMDA antagonists (MK801, AP5) or an AMPA antagonist (YM872) was administered intrathecally, and pups were assessed in the formalin test behaviorally and by Fos expression within the spinal cords of 3-, 10-, and 21-day-old rats.. The NMDA antagonists attenuated formalin-induced behavioral responses at the youngest age tested with some selectivity for the second phase of responding. MK-801 did not induce motor impairment at any age. YM872 also attenuated formalin-induced nociceptive responses at all ages throughout the test session, although there was some motor impairment in the 3-day-old subjects. Spinal administration of either YM872 or MK-801 reduced Fos expression in the spinal cord at all ages.. These data suggest that spinal NMDA and AMPA receptor are functional and involved in formalin-induced nociception throughout development.

Topics: Age Factors; Animals; Animals, Suckling; Behavior, Animal; Dizocilpine Maleate; Imidazoles; Motor Activity; Pain; Pain Measurement; Quinoxalines; Rats; Rats, Long-Evans; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Spinal Cord

Previous research has shown that the hippocampus processes pain related-information, probably through hippocampal neurons that respond exclusively to painful stimulation. In the current experiments we tested whether blocking NMDA receptors in the hippocampal CA1 region and dentate gyrus could reduce nociceptive behaviors in rats. The competitive and noncompetitive NMDA receptor antagonists 2-amino-5-phosphonopentanoic acid (AP5; 3.75 microg/0.75 microl) and MK801 (1.5, 3, 6 microg/0.5 microl) were injected into the dentate gyrus and CA1 area of behaving rats 5 min before subcutaneous injection of formalin irritant. Pain behaviors in both acute and tonic phases of the formalin test were significantly reduced by AP5 (3.75 microg/0.75 microl) and MK801 (3 microg/0.5 microl, but not 1.5 and 6 microg/0.5 microl) injection to the dentate gyrus. In the CA1, injection of AP5 had no effect while injection of the effective dose of MK801 (3 microg/0.5 microl) had a significant antinociceptive effect. This effect was apparent only during the late phase of the formalin test. These results support the hypothesis that NMDA-sensitive mechanisms are involved in acute and persistent pain-related processing in the dentate gyrus and with tonic pain processing in the hippocampal CA1 region.

Topics: 2-Amino-5-phosphonovalerate; Analgesics; Animals; Dentate Gyrus; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Formaldehyde; Hippocampus; Male; Microinjections; Models, Anatomic; Pain; Pain Measurement; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Time Factors

Oleoylethanolamide (OEA) is a natural fatty acid amide that mainly modulates feeding and energy homeostasis by binding to peroxisome proliferator-activated receptor-alpha (PPAR-alpha) [Rodríguez de Fonseca F, Navarro M, Gómez R, Escuredo L, Navas F, Fu J, et al. An anorexic lipid mediator regulated by feeding. Nature 2001;414:209-12; Fu J, Gaetani S, Oveisi F, Lo Verme J, Serrano A, Rodríguez de Fonseca F, et al. Oleoylethanolamide regulates feeding and body weight through activation of the nuclear receptor PPAR-alpha. Nature 2003;425:90-3]. Additionally, it has been proposed that OEA could act via other receptors, including the vanilloid receptor (TRPV1) [Wang X, Miyares RL, Ahern GP. Oleoylethanolamide excites vagal sensory neurones, induces visceral pain and reduces short-term food intake in mice via capsaicin receptor TRPV1. J Physiol 2005;564:541-7.] or the GPR119 receptor [Overton HA, Babbs AJ, Doel SM, Fyfe MC, Gardner LS, Griffin G, et al. Deorphanization of a G protein-coupled receptor for oleoylethanolamide and its use in the discovery of small-molecule hypophagic agents. Cell Metab 2006;3:167-175], suggesting that OEA might subserve other physiological roles, including pain perception. We have evaluated the effect of OEA in two types of nociceptive responses evoked by visceral and inflammatory pain in rodents. Our results suggest that OEA has analgesic properties reducing the nociceptive responses produced by administration of acetic acid and formalin in two experimental animal models. Additional research was performed to investigate the mechanisms underlying this analgesic effect. To this end, we evaluated the actions of OEA in mice null for the PPAR-alpha receptor gene and compared its actions with those of PPAR-alpha receptor wild-type animal. We also compared the effect of MK-801 in order to evaluate the role of NMDA receptor in this analgesia. Our data showed that OEA reduced visceral and inflammatory responses through a PPAR-alpha-activation independent mechanism. Co-administration of subanalgesic doses of MK-801 and OEA produced an analgesic effect, suggesting the participation of glutamatergic transmission in the antinociceptive effect of OEA. This study represents a novel approach to the examination of the effectiveness of OEA in nociceptive responses and provides a framework for understanding its biological functions and endogenous targets in visceral and inflammatory pain.

Topics: Analgesics; Animals; Anticholesteremic Agents; Behavior, Animal; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Endocannabinoids; Excitatory Amino Acid Antagonists; Exploratory Behavior; Inflammation; Male; Mice; Mice, Knockout; Morphine; Oleic Acids; Pain; Pain Measurement; PPAR gamma; Pyrimidines

Intrathecal (i.t.) administration of D-cycloserine (100 and 300 fmol), a partial agonist of the glycine recognition site on the N-methyl-D-aspartate (NMDA) receptor ion-channel complex, produced a behavioral response mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank in mice, which peaked at 5 - 10 min and almost disappeared at 15 min after the injection. The behavior induced by D-cycloserine (300 fmol) was dose-dependently inhibited by an intraperitoneal injection of morphine (0.5-2 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also dose-dependently inhibited by i.t. co-administration of 7-chlorokynurenic acid (0.25-4 nmol), a competitive antagonist of the glycine recognition site on the NMDA receptor ion-channel complex; D-(-)-2-amino-5-phosphonovaleric acid (62.5-500 pmol), a competitive NMDA receptor antagonist; MK-801 (62.5-500 pmol), an NMDA ion-channel blocker; ifenprodil (0.5-8 nmol); arcaine (31-125 pmol); and agmatine (0.1-10 pmol), all being antagonists of the polyamine recognition site on the NMDA receptor ion-channel complex. However, [D-Phe7,D-His9]-substance P(6-11), a specific antagonist for substance P (NK1) receptors, and MEN-10,376, a tachykinin NK2-receptor antagonist, had no effect on D-cycloserine-induced nociceptive behavior. These results in the mouse spinal cord suggest that D-cycloserine-induced nociceptive behavior is mediated through the activation of the NMDA receptor ion-channel complex by acting on the glycine recognition site and that it does not involve the tachykinin receptor mechanism.

Topics: 2-Amino-5-phosphonovalerate; Agmatine; Animals; Cycloserine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Injections, Spinal; Ion Channels; Kynurenic Acid; Mice; Morphine; Neurokinin A; Nociceptors; Pain; Peptide Fragments; Piperidines; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Receptors, Tachykinin; Substance P

Opioids are extensively used analgesics yet can paradoxically increase pain sensitivity in humans and rodents. This hyperalgesia is extensively conceptualized to be a consequence of opioid receptor activity, perhaps providing an adaptive response to analgesia, and to utilize N-methyl-D-aspartate (NMDA) receptors. These assumptions were tested here in opioid receptor triple knock-out (KO) mice lacking all three genes encoding opioid receptors (mu, delta, and kappa) by comparing their thermal nociceptive responses to the opioids morphine and oxymorphone with those of B6129F(1) controls. Injecting acute opioid bolus doses in controls caused maximal analgesia that was completely abolished in KO mice, confirming the functional consequence of the KO mouse opioid receptor deficiency. Continuous opioid infusion by osmotic pump in control mice also initially caused several consecutive days of analgesia that was shortly thereafter followed by several consecutive days of hyperalgesia. In contrast, continuously infusing KO mice with opioids caused no detectable analgesic response, but only immediate and steady declines in nociceptive thresholds culminating in several days of unremitting hyperalgesia. Finally, injecting the non-competitive NMDA receptor antagonist MK-801 during opioid infusion markedly reversed hyperalgesia in control but not KO mice. These data demonstrate that sustained morphine and oxymorphone delivery causes hyperalgesia independently of prior or concurrent opioid or NMDA receptor activity or opioid analgesia, indicating the contribution of mechanisms outside of current conceptions, and are inconsistent with proposals of hyperalgesia as a causative factor of opioid analgesic tolerance.

Topics: Analgesics, Opioid; Animals; Data Interpretation, Statistical; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hyperalgesia; Mice; Mice, Knockout; Morphine; Oxymorphone; Pain; Pain Measurement; Reaction Time; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid

The present study investigated the involvement of spinal glutamate receptors in the induction and maintenance of the pain-related behaviors induced by the venom of scorpion Buthus martensi Karsch (BmK). (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5-10-imine hydrogen maleate (MK-801; 40nmol; a non-competitive NMDA receptor antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 40nmol; a non-NMDA receptor antagonist), dl-amino-3-phosphonopropionic acid (dl-AP3; 100nmol; a group I metabotropic glutamate receptor antagonist) and 4-aminopyrrolidine-2,4-dicarboxylate (APDC; 100nmol; a group II metabotropic glutamate receptor agonist) were employed. On intrathecal injection of glutamate receptor antagonists/agonist before BmK venom administration by 10min, BmK venom-induced spontaneous nociceptive responses could be suppressed by all tested agents. Primary thermal hyperalgesia could be inhibited by MK-801 and dl-AP3, while bilateral mechanical hyperalgesia could be inhibited by CNQX and dl-AP3 and contralateral mechanical hyperalgesia could be inhibited by APDC. On intrathecal injection of glutamate receptor antagonists/agonist after BmK venom injection by 4.5h, primary thermal hyperalgesia could be partially reversed by all tested agents, while bilateral mechanical hyperalgesia could only be inhibited by APDC. The results suggest that the role of spinal glutamate receptors may be different on the various manifestations of BmK venom-induced pain-related behaviors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Pain; Proline; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Scorpion Venoms

Changes in the expression of many genes underlie injury-elicited plasticity in the spinal dorsal horn. Homer1 is a recently identified gene that appears to play a critical role in the expression of synaptic plasticity in several brain regions, including the hippocampus. In this study we investigated the early consequences of chronic constriction injury of the sciatic nerve on Homer1 gene expression in the spinal dorsal horn. Significant increases in Homer1a mRNA levels in the ipsilateral dorsal horn were detected at 4h post-ligation, and these levels remained elevated at 8h before returning to baseline values by 24h after the ligation. In contrast, the levels of Homer1b/c mRNA did not change at any of these selected post-ligation times. The ligation-associated induction of Homer1a was dependent on activation of NMDA receptors and the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway. The non-competitive NMDA-receptor antagonist, MK-801, and a specific inhibitor of the ERK1/2 pathway, U0126, significantly attenuated the injury-elicited increases in Homer1a mRNA when compared to saline-treated animals. These data provide the first evidence for a potential role of Homer1a in peripheral nerve injury-elicited plasticity in the spinal dorsal horn. These data also imply that the early and transient up-regulation of Homer1a gene expression may be an important contributor to the eventual development of neuropathic pain.

Topics: Animals; Butadienes; Carrier Proteins; Constriction, Pathologic; Dizocilpine Maleate; Homer Scaffolding Proteins; Ligation; Male; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Neuronal Plasticity; Nitriles; Pain; Peripheral Nervous System Diseases; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; RNA, Messenger; Sciatic Nerve; Up-Regulation

Increasing evidence supports a possible role for nitric oxide (NO) in the transmission of pain signals and in the development of central mechanisms of hyperalgesia. Previously, we have shown that nitroglycerin, an NO donor, is able to induce a long-lasting hyperalgesic state in rats. Nitroglycerin-induced hyperalgesia can be detected as an increase in the nociceptive behavior evoked by the formalin test. In the present study we investigated the possible mediators in the nitroglycerin-induced hyperalgesic state. Male Sprague-Dawley rats were injected with nitroglycerin and pretreated with indomethacin, 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate (MK-801) or N(omega)-nitro-L-arginine methyl ester (L-NAME). The results obtained showed that inhibition of prostaglandins or NO synthesis prevents nitroglycerin-induced hyperalgesia in Phase II of the formalin test. A similar inhibitory effect was also observed following pretreatment with the glutamate antagonist MK801. The present findings point to the role of prostaglandins, NO synthesis and glutamate activity in the induction of nitroglycerin-induced hyperalgesia.

Topics: Animals; Cyclooxygenase Inhibitors; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Formaldehyde; Glutamic Acid; Hyperalgesia; Indomethacin; Male; Models, Animal; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroglycerin; Pain; Prostaglandin-Endoperoxide Synthases; Prostaglandins; Rats; Rats, Sprague-Dawley

Stimulation of the greater occipital nerve produces excitation of second order neurons in the trigeminocervical complex. Given that neck pain is very common in primary headache disorders, this convergent excitation may play a role in pain referral from cervical structures. While previous studies have demonstrated a physiological model for this convergence, this study sought an anatomical approach to examine the distribution of second order neurons in the trigeminocervical complex receiving greater occipital nerve input. In addition, the role of glutamatergic NMDA receptor activation within the trigeminocervical complex in response to cervical afferents was studied. Noxious stimulation of the occipital muscle in rat using mustard oil and mineral oil produced significantly altered Fos expression in the trigeminocervical complex compared with the surgical control (H(4)=31.3, P<0.001, Kruskal-Wallis). Baseline expression was 11 (median, range 4, 17) fos positive cells in the trigeminocervical complex, occipital muscle treated with mustard oil produced 23 (17, 33) and mineral oil a smaller effect of 19 (15, 25) fos positive cells, respectively (P=0.046). The effects of both mustard and mineral oil were reversed by the NMDA-receptor antagonist MK801. This study introduces a model for examining trigeminocervical complex activity after occipital afferent stimulation in the rat that has good anatomical resolution and demonstrates involvement of glutamatergic NMDA receptors at this important synapse.

Topics: Afferent Pathways; Animals; Dizocilpine Maleate; Immunohistochemistry; Male; Mineral Oil; Mustard Plant; Neck Muscles; Neurons; Pain; Plant Oils; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Nerves; Trigeminal Nuclei

The effect of aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, on morphine-induced tolerance and dependence in mice was investigated in this study. Acute administration of aminoguanidine (20 mg/kg, p.o.) did not affect the antinociceptive effect of morphine (10 mg/kg, s.c.) as measured by the hot plate test. Repeated administration of aminoguanidine along with morphine attenuated the development of tolerance to the antinociceptive effect of morphine. Also, the development of morphine dependence as assessed by naloxone-precipitated withdrawal manifestations was reduced by co-administration of aminoguanidine. The effect of aminoguanidine on naloxone-precipitated withdrawal was enhanced by concurrent administration of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, dizocilpine (0.25 mg/kg, i.p.) or the non-specific nitric oxide synthase (NOS) inhibitor, l-N(G)-nitroarginine methyl ester (l-NAME; 5 mg/kg, i.p.) and antagonized by concurrent administration of the nitric oxide (NO) precursor, l-arginine (50 mg/kg, p.o.). Concomitantly, the progressive increase in NO production, but not in brain glutamate level, induced by morphine was inhibited by repeated administration of aminoguanidine along with morphine. Similarly, co-administration of aminoguanidine inhibited naloxone-induced NO overproduction, but it did not inhibit naloxone-induced elevation of brain glutamate level in morphine-dependent mice. The effect of aminoguanidine on naloxone-induced NO overproduction was potentiated by concurrent administration of dizocilpine or l-NAME and antagonized by concurrent administration of l-arginine. These results provide evidence that blockade of NO overproduction, the consequence of NMDA receptor activation, by aminoguanidine, via inhibition of iNOS, can attenuate the development of morphine tolerance and dependence.

Topics: Analgesics; Analgesics, Opioid; Animals; Arginine; Behavior, Animal; Brain; Dizocilpine Maleate; Drug Tolerance; Enzyme Inhibitors; Glutamates; Guanidines; Male; Mice; Morphine; Morphine Dependence; Naloxone; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitrites; Pain; Pain Measurement; Time Factors

Partial peripheral nerve injury often leads to chronic pain states, including allodynia and hyperalgesia. The purpose of this study was to investigate the involvement of the N-methyl-D-aspartate and opioid receptors in the behavioural responses following chronic constriction nerve injury (CCI). The animals were injected a combination of MK-801 (0.3 mg/kg, 20 min before, and 6 h after the operation) and morphine (8 mg/kg, 30 min prior to the operation) and were tested for allodynia and hyperalgesia reactions at 0, 3, 7, 14, 21 and 28 days after CCI. Compound action potentials were also recorded from the injured nerve 2 weeks post-operation to indicate nerve injury state electrophysiologically. Our results indicate that the CCI model importantly influences the behavioural responses to both the thermal and mechanical stimulations. Also, the pre-emptive co-administration of MK-801 and morphine has suppressive effects on the cold allodynia but a slight alleviation on the mechano-allodynia and heat hyperalgesia.

Topics: Action Potentials; Analgesics, Opioid; Animals; Cold Temperature; Constriction, Pathologic; Dizocilpine Maleate; Electrophysiology; Excitatory Amino Acid Antagonists; Hyperalgesia; Male; Morphine; Pain; Peripheral Nervous System Diseases; Physical Stimulation; Rats; Rats, Sprague-Dawley

Allodynia or hyperalgesia induced by peripheral nerve injury may be involved in changes in the sensitivity of neurotransmitters at the spinal cord level. In order to clarify the functional role of neurotransmitters in peripheral nerve injury, we used rats with nerve injury induced by chronic constriction of the sciatic nerve (CCI rat model) and estimated the effects of the intrathecal injection of drugs known to affect glutamate and tachykinin receptors. In sham-operated rats, the NMDA receptor agonist NMDA and AMPA-kinate receptor agonist RS-(5)-bromowillardin reduced withdrawal latency. The non-competitive NMDA receptor antagonist MK-801, competitive NMDA receptor antagonist AP-5 and AMPA-kinate receptor antagonist NBQX increased withdrawal latency. Substance P (SP) increased the withdrawal latency but only transitorily. The NK1 receptor antagonist RP67580 increased withdrawal latency, but the NK2 receptor antagonist SR48968 did not show an effect. In CCI rats, RS-(5)-bromowillardin reduced withdrawal latency, but NMDA did not show an effect. NBQX increased withdrawal latency, while MK-801 and AP-5 showed little or no effect. SP reduced withdrawal latency, and both RP67580 and SR48968 increased it. These results indicate that the alteration in sensitivity of ionotropic glutamate receptors and tachykinin receptors in the spinal cord contribute to development and maintenance of nerve injury-evoked neuropathic pain.

Topics: Alanine; Analgesics; Animals; Behavior, Animal; Benzamides; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Indoles; Isoindoles; Male; N-Methylaspartate; Pain; Pain Measurement; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, Tachykinin; Sciatic Nerve; Spinal Cord; Substance P; Valine

Morphine analgesic tolerance is heritable in both humans and rodents, with some individuals and strains exhibiting little and others exhibiting robust tolerance. 129S6/SvEv and 129P3/J mice reportedly do not demonstrate tolerance to morphine analgesia. Using our laboratory's standard morphine tolerance regimen and a between-subjects design, tolerance developed in the hot plate and tail withdrawal assays as indicated by a change in analgesic efficacy following a morphine challenge dose. Furthermore, the non-competitive NMDA receptor antagonist MK-801 (dizocilipine) blocked morphine tolerance in 129S6/SvEv and CD-1 mice in the hot plate assay. As previously reported, when a within-subjects design and cumulative dosing was employed, no tolerance was observed in the 129P3/J strain. However, using the same morphine regimen and a between-subjects design, comparable tolerance developed between 129P3/J and C57BL/6J strains following a single challenge dose of morphine. Spontaneous hyperalgesia was observed in the tail withdrawal assay following chronic morphine in C57BL/6J, but not 129P3/J mice. Additionally, morphine-tolerant C57BL/6J mice, but not 129P3/J mice, exhibited a large increase in the frequency of tail flicks during the first second following the baseline nociceptive response which may facilitate detection of the response during the tolerant state. We conclude that the method of tolerance assessment affects the ability to detect tolerance and thus may affect the degree and pattern of heritability of this trait and this could have implications for gene mapping studies.

Topics: Analgesics, Opioid; Animals; Dizocilpine Maleate; Drug Tolerance; Female; Male; Mice; Morphine; Pain; Pain Measurement; Receptors, N-Methyl-D-Aspartate; Species Specificity

I and coauthor previously reported the memory facilitation effect of morphine. The main purpose of this study was to evaluate the involvement of the N-methyl-D-aspartate (NMDA) receptor in associative tolerance to morphine by a contextual procedure. Antinociceptive response latency was measured by the tail-pinch method during repeated morphine (5 mg/kg, s.c.) injection for four consecutive days with pretreatment by dizocilpine (0.01, 0.05, 0.1 mg/kg, i.p.) at 30 min prior to morphine injection in the training phase and before and after morphine injection in the test phase. The nociceptive response latency was shortened by the single administration of dizocilpine (0.05 to 0.25 mg/kg, i.p.). Pretreatment by dizocilpine at 0.05 or 0.1 mg/kg weakened the antinociception to morphine on Day 1, but decreased the tolerance throughout the training phase. In the test phase, the animals were allocated into the same and different contexts. In the test phase, hyperalgesia before morphine injection in the same context and antinociception after morphine injection in the different context were evident in the saline-pretreated group in the training phase, but they were not observed in those contexts in the dizocilpine-pretreated groups. These results suggest that memory dysfunction with dizocilpine inhibits the recovery of associative tolerance to morphine by contextual change.

Topics: Animals; Dizocilpine Maleate; Drug Administration Schedule; Drug Evaluation, Preclinical; Drug Tolerance; Hyperalgesia; Injections, Intraperitoneal; Injections, Subcutaneous; Male; Memory; Mice; Morphine; Pain; Pain Threshold; Reaction Time; Receptors, N-Methyl-D-Aspartate; Tail

Central glucocorticoid receptors (GRs) and NMDA receptors (NMDARs) have been shown to play a significant role in the mechanisms of neuropathic pain after peripheral nerve injury; however, how central GRs and NMDARs interact in this process remains unknown. Here we show that the expression and function of spinal NMDARs after peripheral nerve injury were modulated by central GRs. Chronic constriction nerve injury (CCI) in rats induced a time-dependent upregulation of NR1 and NR2 subunits of the NMDAR within the spinal cord dorsal horn ipsilateral to CCI. The upregulation of NMDARs was significantly diminished by intrathecal administration (twice daily for postoperative days 1-6) of either the GR antagonist RU38486 or an antisense oligonucleotide against GRs. Moreover, this CCI-induced expression of NMDARs was significantly attenuated in rats receiving intrathecal treatment with an interleukin-6 (IL-6) antiserum and in mice with protein kinase Cgamma (PKCgamma) knock-out. Because IL-6 and PKCgamma mediated the upregulation of central GRs after CCI as demonstrated previously, the results suggest that IL-6 and PKCgamma served as cellular mediators contributing to the GR-mediated expression of NMDARs after CCI. Functionally, nociceptive behaviors induced by NMDAR activation and CCI were reversed by a single intrathecal administration of the GR antagonist RU38486. Conversely, a single intrathecal injection with the noncompetitive NMDAR antagonist MK-801 reversed neuropathic pain behaviors exacerbated by the GR agonist dexamethasone in CCI rats. These data suggest that interactions between central GRs and NMDARs through genomic and nongenomic regulation may be an important mechanism critical to neuropathic pain behaviors in rats.

Topics: Animals; Behavior, Animal; Constriction; Dizocilpine Maleate; Hyperalgesia; Interleukin-6; Male; Mice; Mice, Knockout; Mifepristone; Oligodeoxyribonucleotides, Antisense; Pain; Peripheral Nerve Injuries; Peripheral Nervous System Diseases; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Glucocorticoid; Receptors, N-Methyl-D-Aspartate; Spinal Cord

The experiment explored the influence of glutamic acid (Glu) and the NMDA-receptor antagonist dizocilpine maleate (MK-801) on the pain-evoked responses of pain-excitation neurons (PEN) in the nucleus accumbens (NAc) of rats. The trains of electric impulses applied to the sciatic nerve were used as noxious stimulation. The discharges of PEN in NAc were recorded by glass microelectrode. We observed the influence of intracerebroventricular (icv) injection of Glu and microinjection of MK-801 into the NAc on the noxious stimulation-evoked activities of PEN in NAc. The results showed that the noxious stimulation potentiated the electric activities of PEN in NAc. Intracerebroventricular injection of Glu (10 nmol/10 microl) increased the frequency of the discharge of PEN evoked by the noxious stimulation in NAc, the Glu-induced response was blocked by the injection of MK-801 (1.0 nmol/0.5 microl) into NAc. MK-801 partly inhibited the response of PEN upon the noxious stimulation. It is therefore suggested that the facilitatory effect of Glu on PEN response in NAc to the noxious stimulation is mediated by NMDA receptors, and that Glu and NMDA receptors are involved in the modulation of nociceptive information transmission in the NAc.

Topics: Animals; Dizocilpine Maleate; Electric Stimulation; Electrophysiological Phenomena; Female; Glutamic Acid; Male; Neurons; Nociceptors; Nucleus Accumbens; Pain; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Secondary mechanical allodynia induced by intradermal injection of capsaicin has been widely used to search for the underlying mechanisms of tissue injury induced mechanical allodynia. However, the capsaicin concentration dependency of the development of secondary mechanical allodynia and the underlying mechanisms of development and maintenance of capsaicin-induced mechanical allodynia are not fully understood. In the present study, we clarify the capsaicin concentration dependency for development and maintenance of secondary mechanical allodynia and the role of spinal opioid receptor like1 (ORL1) receptor and N-methyl-D-aspartate receptor in the development and maintenance of secondary mechanical allodynia induced by an intradermal capsaicin injection. Capsaicin 50 microL of 0.03% induced the most intense secondary mechanical allodynia. Intrathecal injection of nociceptin, an ORL1 receptor agonist, attenuated the maintenance of secondary mechanical allodynia but had no effect on the development of secondary mechanical allodynia. An intrathecal injection of MK801, an N-methyl-D-aspartate receptor antagonist, had no effect on the development and maintenance of secondary mechanical allodynia. These findings suggest that spinal ORL1 receptor should be the target of study for the treatment of secondary mechanical allodynia induced by tissue injury.

Topics: Animals; Behavior, Animal; Capsaicin; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Foot; Injections, Intradermal; Male; Nociceptin; Nociceptin Receptor; Opioid Peptides; Pain; Physical Stimulation; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Spinal Cord

Interactions between adenosine receptor ligands and dizocilpine (uncompetitive NMDA receptor antagonist) was studied in antinociceptive, writhing test in mice. Minimal effective, antinociceptive doses of adenosine receptor agonists were: 0.1 mg/kg (NECA--A1/A2 agonist). Generally, these agonists did not potentiate the subthreshold dose of dizocilpine (0.05 mg/kg). Of all adenosine receptor antagonists used, only caffeine (A2 and A2 antagonists) reversed dizocilpine-induced (0.1 mg/kg) antinociception dose-dependently. These findings indicate that dizocilpin-induced antinociception in the writhing test is only partly influenced by adenosine receptor ligands.

Topics: Acetic Acid; Animals; Behavior, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Male; Mice; Nociceptors; Pain; Purinergic P1 Receptor Agonists; Receptors, Purinergic P1; Theobromine; Xanthines

NMDA receptors are involved in the modulation of neuropathic pain behavior and central sensitization. In vivo, this is mostly demonstrated by the use of specific antagonists such as MK801. Because studies evaluating the direct impact of spinal NMDA in neuropathic pain models are lacking, we performed a series of experiments to study the role of spinal NMDA injection on existing cold allodynia, as a measurement of neuropathic pain behavior in rodents. Intrathecal injection of NMDA resulted in an enhanced neuropathic pain behavior in CCI rats on a cold plate. The activity was present from a dose of 5 ng/rat onward and could selectively be reversed by intraperitoneal injections of doses of > or = 0.01 mg/kg MK801. These results support the regulatory role of NMDA receptors in the hypersensitivity to cold observed in neuropathic pain behavior in rodents.

Topics: Animals; Cold Temperature; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Injections, Spinal; Male; N-Methylaspartate; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Sciatic Neuropathy

1. Supraspinal opioid antinociception is mediated, in part, by connections between the periaqueductal grey (PAG) and the rostral ventromedial medulla (RVM). Morphine antinociception from the PAG is decreased by serotonin, N-methyl-d-aspartate (NMDA) and opioid receptor antagonists administered into the RVM. Because the brain isoform of nitric oxide synthase (NOS) is also prominent in the RVM, the present study was designed to evaluate the effects of microinjection of the non-selective NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) and the non-competitive NMDA receptor antagonist MK-801 into the RVM on PAG morphine antinociception and their potential interactions, as measured by the tail-flick test. 2. Rats were anaesthetized with sodium pentobarbital and then special cannulas were inserted stereotaxically into the RVM and PAG. After 1 week recovery, the effects of microinjection of MK-801 and l-NAME into the RVM and their interactions in altering PAG morphine (2.5 microg) antinociception elicited from the PAG were assessed. 3. Mesencephalic morphine antinociception was significantly reduced after pretreatment with l-NAME (0.6-1.3 micromol) or MK-801 (0.8 nmol). The reduction in mesencephalic morphine antinociception when MK-801 (0.8 nmol) and l-NAME (1 micromol) were microinjected sequentially into the RVM was not significantly different from the effects of MK-801 (0.8 nmol) or l-NAME (1 micromol) administered alone. 4. These data imply that NMDA receptors and nitric oxide production in the RVM modulate the transmission of opioid pain-inhibitory signals from the PAG.

Topics: Analgesics, Opioid; Animals; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Male; Medulla Oblongata; Microinjections; Morphine; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Pain; Pain Measurement; Periaqueductal Gray; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Signal Transduction

Protein kinase C (PKC) is able to phosphorylate several cellular components that serve as key regulatory components in signal transduction pathways of nociceptor excitation and sensitisation. Therefore, the present study attempted to assess some of the mechanisms involved in the overt nociception elicited by peripheral administration of the PKC activator, phorbol 12-myristate 13-acetate (PMA), in mice. The intraplantar (i.pl.) injection of PMA (16-1600 pmol/paw), but not its inactive analogue alpha-PMA, produced a long-lasting overt nociception (up to 45 min), as well as the activation of PKCalpha and PKCepsilon isoforms in treated paws. Indeed, the local administration of the PKC inhibitor GF109203X completely blocked PMA-induced nociception. The blockade of NK1, CGRP, NMDA, beta1-adrenergic, B2 or TRPV1 receptors with selective antagonists partially decreased PMA-induced nociception. Similarly, COX-1, COX-2, MEK or p38 MAP kinase inhibitors reduced the nociceptive effect produced by PMA. Notably, the nociceptive effect promoted by PMA was diminished in animals treated with an antagonist of IL-1beta receptor or with antibodies against TNFalpha, NGF or BDNF, but not against GDNF. Finally, mast cells as well as capsaicin-sensitive and sympathetic fibres, but not neutrophil influx, mediated the nociceptive effect produced by PMA. Collectively, the results of the present study have shown that PMA injection into the mouse paw results in PKC activation as well as a relatively delayed, but long-lasting, overt nociceptive behaviour in mice. Moreover, these results demonstrate that PKC activation exerts a critical role in modulating the excitability of sensory neurons.

Topics: Adrenergic beta-Antagonists; Analgesics; Animals; Antibodies; Behavior, Animal; Blotting, Western; Bradykinin; Calcitonin Gene-Related Peptide; Capsaicin; Chelating Agents; Dipeptides; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Egtazic Acid; Enzyme Activation; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Extracellular Signal-Regulated MAP Kinases; Guanethidine; Indoles; Male; Mice; Nociceptors; Pain; Pain Measurement; Peptide Fragments; Propranolol; Protein Kinase C; Ruthenium Red; Salicylates; Sympatholytics; Tetradecanoylphorbol Acetate; Time Factors

Adenosine and excitatory amino acids have been known to be involved in modulating nociceptive transmission at the spinal level. The authors assessed the characteristics of the interaction of the adenosine-excitatory amino acid antagonist combinations in the spinal cord of rats on the formalin-induced nociception. Intrathecal NMDA antagonist ((5R, 10S)-(+)-5-methyl-10,11-dihydro-(5)H-dibenzo[a[,]d]cyclohepten-5,10-imine hydrogen maleate, MK801, 30 microg) and AMPA antagonist (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[F]quinoxaline-7-sulfonamide, NBQX, 3 microg) decreased the total number of flinches during both phases in the formalin test. Intrathecal adenosine (300 microg) had little effect on the phase 1 flinching response, but decreased the phase 2 response. The fixed dose analysis and the isobolographic analysis revealed that adenosine interacts additively with MK801 and NBQX in the spinal cord.

Topics: Adenosine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Excitatory Amino Acid Antagonists; Formaldehyde; Injections, Spinal; Male; N-Methylaspartate; Pain; Quinoxalines; Rats; Rats, Sprague-Dawley

Excitatory amino acids (EAAs) are involved in the development of opioid tolerance. The present study reveals that an increasing of CSF EAAs concentration might be responsible for the losing of morphine's antinociceptive effect in morphine tolerant rats. Male Wistar rats were implanted with two intrathecal (i.t.) catheters and one microdialysis probe, then continuously infused i.t. for 5 days with saline (1 microl/h; control group), morphine (15 micrograms/h), the NMDA antagonist, MK-801 (5 micrograms/h), or morphine (15 micrograms/h) plus MK-801 (5 micrograms/h). Each day, tail-flick responses were measured; in addition, CSF dialysates were collected and CSF amino acids measured by high performance liquid chromatography using a fluorescence detector. Morphine started to lose its analgesic effect on day 2 and this effect was overcome by MK-801. The AD(50) (AD: analgesic dose) was 1.33 micrograms in control animals, 83.83 micrograms in morphine-tolerant rats (a 63-fold shift), and 11.2 micrograms (a 8.4-fold shift) in rats that had received MK-801 plus morphine. No significant differences were observed in CSF amino acid release between the groups from day 1 to day 5. On day 5, after basal dialysate collection, a 10-micrograms challenge of morphine was administered i.t., and CSF samples collected over the next 3 h. After morphine challenge, morphine-tolerant rats showed a significant increase in the release of glutamate and aspartate (131+/-9.5% and 156+/-12% of basal levels, respectively), and no antinociceptive effect in the tail-flick latency test, while MK-801/morphine co-infused rats showed no increase in morphine-induced EAA release and a partial antinociceptive effect (MPE=40%). The present study provides direct evidence for a relationship between EAA release and a lack of an antinociceptive response to morphine, and shows that the NMDA antagonist, MK-801, attenuates both of these effects.

Topics: Analgesics, Opioid; Animals; Aspartic Acid; Chromatography, High Pressure Liquid; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Tolerance; Excitatory Amino Acid Antagonists; Excitatory Amino Acids; Glutamic Acid; Injections, Spinal; Male; Microdialysis; Morphine; Pain; Pain Measurement; Rats; Rats, Wistar; Time Factors

Intrathecal (i.t.) pretreatment with a low dose (0.3 nmol) of morphine causes an attenuation of i.t. morphine-produced analgesia; the phenomenon has been defined as morphine-induced antianalgesia. The opioid-produced analgesia was measured with the tail-flick (TF) test in male CD-1 mice. Intrathecal pretreatment with low dose (0.3 nmol) of morphine time dependently attenuated i.t. morphine-produced (3.0 nmol) TF inhibition and reached a maximal effect at 45 min. Intrathecal pretreatment with morphine (0.009-0.3 nmol) for 45 min also dose dependently attenuated morphine-produced TF inhibition. The i.t. morphine-induced antianalgesia was dose dependently blocked by the nonselective mu-opioid receptor antagonist (-)-naloxone and by its nonopioid enantiomer (+)-naloxone, but not by endomorphin-2-sensitive mu-opioid receptor antagonist 3-methoxynaltrexone. Blockade of delta-opioid receptors, kappa-opioid receptors, and N-methyl-D-aspartate (NMDA) receptors by i.t. pretreatment with naltrindole, nor-binaltorphimine, and (-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801), respectively, did not affect the i.t. morphine-induced antianalgesia. Intrathecal pretreatment with antiserum against dynorphin A(1-17), [Leu]-enkephalin, [Met]-enkephalin, beta-endorphin, cholecystokinin, or substance P also did not affect the i.t. morphine-induced antianalgesia. The i.t. morphine pretreatment also attenuated the TF inhibition produced by opioid muagonist [D-Ala2, N-Me-Phe4,Gly-ol5]-enkephalin, delta-agonist deltorphin II, and kappa-agonist U50,488H. It is concluded that low doses (0.009-0.3 nmol) of morphine given i.t. activate an antianalgesic system to attenuate opioid mu-, delta-, and kappa-agonist-produced analgesia. The morphine-induced antianalgesia is not mediated by the stimulation of opioid mu-, delta-, or kappa-receptors or NMDA receptors. Neuropeptides such as dynorphin A(1-17), [Leu]-enkephalin, [Met]-enkephalin, beta-endorphin, cholecystokinin, and substance P are not involved in this low-dose morphine-induced antianalgesia.

Topics: Analgesia; Animals; beta-Endorphin; Dizocilpine Maleate; Drug Interactions; Drug Tolerance; Dynorphins; Enkephalins; Male; Mice; Morphine; Naloxone; Naltrexone; Oligopeptides; Pain; Pain Measurement; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Spinal Cord; Substance P

Pharmacological blockade of N-methyl-D-aspartate (NMDA) receptors can modulate morphine analgesia in experimental animals and humans. However, this literature is highly inconsistent, with NMDA receptor antagonists variously shown to potentiate, attenuate or produce no effect on morphine analgesic magnitude. A number of factors influencing this modulation have been proposed, but no one has examined such factors simultaneously, and all existing studies in mice were conducted exclusively in male subjects. Thus, the influence of systemic administration of site-specific NMDA receptor antagonists-including dextromethorphan, dextrorphan, MK-801, LY235959, L-701,324, and Ro 25-6981-on morphine analgesia (15-45 mg/kg; 15, 30 and 60 min post-injection) was studied in male and female mice using the 49 degrees C tail-withdrawal test. We found that oral and intraperitoneal dextromethorphan, a low-affinity non-competitive antagonist, dose-dependently potentiated low-dose morphine analgesia but attenuated high-dose morphine analgesia. Dextrorphan and MK-801 were found to potentiate low- but not high-dose morphine analgesia. The competitive glutamate-site antagonist, LY235959, and glycine-site antagonist, L-701,324, potentiated morphine analgesia at all doses. In contrast, the polyamine (NR2B) site antagonist, Ro 25-6981, attenuated morphine analgesia at all doses. Strikingly, the non-competitive antagonists produced no modulation of morphine analgesia whatsoever in female mice, whereas no sex differences were observed using competitive or NR2B antagonists. These findings indicate that NMDA modulation of morphine analgesia is critically influenced by sex, site of antagonism, morphine dose and time after injection. Our data suggest that NMDA antagonism via competitive or glycine site antagonism might result in more reliable clinical effects on morphine analgesia in both sexes.

Topics: Animals; Central Nervous System; Dextromethorphan; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Excitatory Amino Acid Antagonists; Female; Isoquinolines; Male; Mice; Morphine; Pain; Phenols; Piperidines; Quinolones; Receptors, N-Methyl-D-Aspartate; Sex Characteristics; Time Factors

1. Ingestion of a poisonous mushroom Clitocybe acromelalga is known to cause severe tactile pain (allodynia) in the extremities for a month and acromelic acid (ACRO), a kainate analogue isolated from the mushroom, produces selective damage of interneurons of the rat lower spinal cord when injected either systemically or intrathecally. Since ACRO has two isomers, ACRO-A and ACRO-B, here we examined their acute and late effects on induction of allodynia. 2. Intrathecal administration of ACRO-A and ACRO-B provoked marked allodynia by the first stimulus 5 min after injection, which lasted over the 50-min experimental period. Dose-dependency of the acute effect of ACRO-A on induction of allodynia showed a bell-shaped pattern from 50 ag x kg(-1) to 0.5 pg x kg(-1) and the maximum effect was observed at 50 fg x kg(-1). On the other hand, ACRO-B induced allodynia in a dose-dependent manner from 50 pg x kg(-1) to 50 ng x kg(-1). 3. N-methyl-d-aspartate (NMDA) receptor antagonists and Joro spider toxin, a Ca(2+)-permeable AMPA receptor antagonist, inhibited the allodynia induced by ACRO-A, but not by ACRO-B. However, other AMPA/kainate antagonists did not affect the allodynia induced by ACRO. 4. Whereas no neuronal damage was observed in the spinal cord in ACRO-A-treated mice, induction of allodynia by ACRO-A (50 fg x kg(-1)) and ACRO-B (50 ng x kg(-1)) was selectively lost 1 week after i.t. injection of a sublethal dose of ACRO-A (50 ng x kg(-1)) or ACRO-B (250 ng x kg(-1)). Higher doses of ACRO-A, however, could evoke allodynia dose-dependently from 50 pg x kg(-1) to 500 ng x kg(-1) in the ACRO-A-treated mice. The allodynia induced by ACRO-A (500 ng x kg(-1)) was not inhibited by Joro spider toxin or NMDA receptor antagonists. These properties of the late allodynia induced by ACRO-A were quite similar to those of the acute allodynia induced by ACRO-B. 5. ACRO-A could increase [Ca(2+)](i) in the deeper laminae, rather than in the superficial laminae, of the spinal cord. This increase was not blocked by the AMPA-preferring antagonist GYKI52466 and Joro spider toxin. 6. Taken together, these results demonstrate the stereospecificity of ACRO for the induction of allodynia and suggest the presence of a receptor specific to ACRO.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Basidiomycota; Benzodiazepines; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Glutamates; Heterocyclic Compounds; Indoles; Injections, Spinal; Japan; Kainic Acid; Lumbosacral Region; Male; Mice; Mice, Inbred Strains; Mushroom Poisoning; Oximes; Pain; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Spider Venoms; Spinal Cord; Stereoisomerism; Structure-Activity Relationship; Time Factors

In contrast to conventional opioid analgesics, antagonists acting at the N-methyl-d-aspartate (NMDA) subtype of glutamate receptors are capable of suppressing pain-related phenomena in chronic pain models while having little or no effect on acute nociception. One of the few clinically used NMDA receptor antagonists, memantine, differs from prototypic antagonists with psychotomimetic activity such as phencyclidine and (+)MK-801, in showing lower receptor affinity, faster unblocking kinetics and stronger voltage-dependency. Recently, a series of novel amino-alkyl-cyclohexanes was reported to interact with NMDA receptors in a manner similar to that of memantine. The present study aimed to evaluate the effects of these compounds as well as (+)MK-801 and memantine in two rat models of chronic pain and the rotarod test. Unlike (+)MK-801 and memantine, most of the tested compounds were inactive against tactile allodynia induced by sciatic nerve ligation. On the other hand, all tested drugs were found to inhibit formalin-induced grooming behavior-a model of chronic pain induction. In agreement with previous reports on the effects of NMDA receptor antagonists in similar assays, the late phase seemed to be inhibited to a greater extent than the early phase. For all tested compounds, inhibition of formalin-induced behaviors occurred at dose levels that were also producing significant motor deficits (rotarod test). These results confirm low efficacy of acute administration of NMDA receptor antagonists in the models of established pain states. Thus, studies on the prevention and management of chronic pain should focus on preemptive or long-term administration of NMDA receptor antagonists.

Topics: Animals; Chronic Disease; Dizocilpine Maleate; Electrophysiology; Excitatory Amino Acid Antagonists; Formaldehyde; Grooming; Ligation; Male; Memantine; Oocytes; Pain; Pain Measurement; Postural Balance; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; RNA, Complementary; Sciatic Nerve; Sciatic Neuropathy; Xenopus

Inhibition of somatic nociception by conditioning noxious visceral stimulation was studied under pathophysiological conditions in rats. Viscero-somatic inhibition was enhanced following visceral inflammation and reduced by a somatic heat injury. The enhancement was reversed by an N-methyl-D-aspartate (NMDA) receptor antagonist. These changes in viscero-somatic inhibition may be explained by corresponding changes in excitatory drives evoked by conditioning and test stimulation, although disinhibition may contribute to reduction of inhibition following somatic injury.

Topics: Animals; Burns; Colitis; Colon; Conditioning, Psychological; Dizocilpine Maleate; Down-Regulation; Excitatory Amino Acid Antagonists; Hyperalgesia; Inflammation; Male; Neural Inhibition; Nociceptors; Pain; Physical Stimulation; Rats; Rats, Wistar; Reaction Time; Receptors, N-Methyl-D-Aspartate; Rectum; Reflex; Skin; Synaptic Transmission; Visceral Afferents

Progressive tactile hypersensitivity (PTH) manifesting after sciatic nerve crush and spared nerve injury (SNI) are two distinct rodent experimental models of neuropathic pain. PTH develops months after recovery from the nerve crush in response to repeated intermittent low-threshold mechanical stimulation of the reinnervated sciatic nerve skin territory and represents a model of stimulus-induced pain. SNI is characterized by an early and sustained increase in stimulus-evoked pain sensitivity in the intact skin territory of the spared sural nerve after sectioning of the two other terminal branches of the sciatic nerve. We examined the effects of morphine (0.5-10 mg/kg), gabapentin (30-200 mg/kg), MK801 (0.01-0.02 mg/kg), amitriptyline (10-25 mg/kg), and carbamazepine (5-7.5 mg/kg) in both models. Morphine, gabapentin, and carbamazepine both reversed and prevented stimulus-induced PTH, whereas MK801 and amitriptyline reduced but did not prevent stimulus-induced PTH. In contrast, the stimulus-evoked behavioral hypersensitivity in the SNI model was poorly modified by these drugs. Independent neuropathic pain models show differential sensitivity to analgesic drug treatment. We suggest that this is due to the different mechanisms responsible for the neuropathic pain-related behavior. Multiple models are required, therefore, to study the mechanisms that contribute to neuropathic pain and to predict analgesic efficacy for different components of the neuropathic pain syndrome.

Topics: Acetates; Amines; Analgesics; Analgesics, Opioid; Animals; Cold Temperature; Cyclohexanecarboxylic Acids; Disease Models, Animal; Dizocilpine Maleate; Gabapentin; gamma-Aminobutyric Acid; Hot Temperature; Hyperalgesia; Male; Morphine; Nerve Crush; Neuroprotective Agents; Pain; Pain Measurement; Peripheral Nervous System Diseases; Physical Stimulation; Rats; Rats, Sprague-Dawley; Sciatic Neuropathy

Topics: Animals; Benzamides; Catheterization; Dizocilpine Maleate; Dose-Response Relationship, Drug; Dynorphins; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Nociceptors; Pain; Physical Stimulation; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta

The major local symptom of Phoneutria nigriventer envenomation is an intense pain, which can be controlled by infiltration with local anesthetics or by systemic treatment with opioid analgesics. Previous work showed that intraplantar (i.pl) injection of Phoneutria nigriventer venom in rats induces hyperalgesia, mediated peripherally by tachykinin and glutamate receptors. The present study examined the spinal mechanisms involved in pain-enhancing effect of this venom. Intraplantar injection of venom into rat hind paw induced hyperalgesia. This phenomenon was inhibited by intrathecal (i.t.) injection of tachykinin NK1 (GR 82334) or NK2 (GR 94800) receptor antagonists, a calcitonin gene-related peptide (CGRP) receptor antagonist (CGRP8-37) and N-methyl-D-aspartate (NMDA; MK 801 and AP-5), non-NMDA ionotropic (CNQX), or metabotropic (AIDA and MPEP) glutamate receptor antagonists, suggesting the involvement of spinal neurokinins and excitatory amino acids. The role of proinflammatory cytokines, nitric oxide (NO), and prostanoids in spinally mediated pain facilitation was also investigated. Pharmacological blockade of tumour necrosis factor-alpha (TNFalpha) or interleukin-1beta (IL-1beta) reduced the hyperalgesic response to venom. Intrathecal injection of L-N6-(1-iminoethyl)lysine (L-NIL), but not of 7-nitroindazole (7-NI), inhibited hyperalgesia induced by the venom, indicating that NO, generated by the activity of the inducible form of nitric oxide synthase, also mediates this phenomenon. Furthermore, indomethacin, an inhibitor of cyclooxigenases (COX), or celecoxib, a selective inhibitor of COX-2, abolished venom-induced hyperalgesia, suggesting the involvement of spinal prostanoids in this effect. These data indicate that the spinal mechanisms of pain facilitation induced by Phoneutria nigriventer venom involves a plethora of mediators that may cooperate in the genesis of venom-induced central sensitization.

Topics: Animals; Antibodies; Calcitonin Gene-Related Peptide Receptor Antagonists; Celecoxib; Citrates; Cyclooxygenase Inhibitors; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hyperalgesia; Indazoles; Interleukin-1; Lysine; Male; Neurokinin-1 Receptor Antagonists; Nitric Oxide Synthase; Pain; Physalaemin; Prostaglandins; Pyrazoles; Rats; Rats, Wistar; Receptors, Calcitonin Gene-Related Peptide; Receptors, Neurokinin-1; Spider Venoms; Spinal Cord; Sulfonamides; Tumor Necrosis Factor-alpha

Various studies reported c-Fos expression in the neurons in the trigeminal sensory nuclear complex (TSNC) following experimental tooth movement, which implies pain transmission to the central nervous system. Meanwhile, MK-801, a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, was shown to markedly reduce the expression of c-Fos in the trigeminal subnucleus caudalis (Vc) following noxious stimulation but to enhance c-Fos expression markedly in other brain regions, i.e., the neocortex, dorsal raphe and thalamic nuclei. In the present study, we examined the nature of c-Fos expression in the brainstem including the TSNC and midbrain following administration of MK-801 and/or experimental movement of the rat molars. Twelve hours after the beginning of experimental tooth movement, c-Fos was expressed bilaterally in the superficial laminae of Vc (Vc I/II), dorsomedial areas of the trigeminal subnucleus oralis (Vodm) and rostro-dorsomedial areas of the trigeminal subnucleus oralis (Vor) with the ipsilaterally dominant distribution, but hardly in the periaqueductal gray (PAG), dorsal raphe nucleus (DR) and Edinger-Westphal nucleus (EW). Intraperitoneal administration of MK-801 (0.03, 0.3 and 3.0 mg/kg) prior to the onset of experimental tooth movement reduced c-Fos in the TSNC (Vc I/II, Vodm and Vor) but increased it in the nucleus raphe magnus (NRM), ventrolateral PAG (vl PAG), DR and EW. These results highly emphasize that during experimental tooth movement, a blockade of NMDA receptors induces neuronal suppression in the TSNC but increases neuronal activity in the descending antinociceptive system including the NRM, vl PAG, DR and EW.

Topics: Animals; Brain; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Immunohistochemistry; Male; Mesencephalon; Molar; Neurons; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Tooth Migration; Trigeminal Nuclei

There is a qualitative sex difference in the neurochemical mediation of stress-induced and kappa-opioid analgesia; these phenomena are dependent on N-methyl-d-aspartic acid (NMDA) receptors in males but not females. Progesterone modulation of this sex difference was examined in mice. Analgesia against thermal nociception was produced by forced cold water swim or by systemic administration of the kappa-opioid agonist, U50,488. As seen previously, the NMDA receptor antagonist MK-801 blocked both forms of analgesia in male but not female mice. Also as in previous studies, this sex difference was found to be dependent on ovarian hormones such that ovariectomy induced female mice to "switch" to the male-like, NMDAergic system. We now demonstrate that a single injection of progesterone (50 microg), systemically administered 30 min before analgesia assessment, is sufficient to restore female-specific mediation of analgesia (i.e., insensitivity to MK-801 blockade) in ovariectomized female mice. The rapidity of this neurochemical "switching" action of progesterone suggests mediation via cell surface receptors or the action of neuroactive steroid metabolites of progesterone.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesia; Analgesics, Non-Narcotic; Analysis of Variance; Animals; Brain Chemistry; Castration; Dizocilpine Maleate; Drug Administration Schedule; Excitatory Amino Acid Antagonists; Female; Male; Mice; Ovariectomy; Pain; Progesterone; Reaction Time; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, kappa; Sex Characteristics; Stress, Psychological; Swimming

Morphine is an effective analgesic, but adverse effects limit its clinical use in higher doses. The non-opioid antitussive, dextromethorphan (DM), can potentiate the analgesic effect of morphine and decrease the dose of morphine in acute postoperative pain, but the underlying mechanism remains unclear. We previously observed that DM increases the serum concentration of morphine in rats. Therefore, we investigated the effects of drugs administered at the spinal level to exclude possible pharmacokinetic interactions. As DM has widespread binding sites in the central nervous system [such as N-methyl-D-aspartate (NMDA) receptors, sigma receptors and alpha(3)ss(4) nicotinic receptors], we investigated whether the potentiation of morphine antinociception by DM at the spinal level is related to NMDA receptors.. We used MK-801 as a tool to block the NMDA channel first, and then studied the interaction between intrathecal (i.t.) morphine and DM. The tail-flick test was used to examine the antinociceptive effects of different combinations of morphine and other drugs in rats.. DM (2-20 microg) or MK-801 (5-15 microg) showed no significant antinociceptive effect by themselves. The antinociceptive effect of morphine (0.5 microg, i.t.) was significantly enhanced by DM and reached the maximal potentiation (43.7%-50.4%) at doses of 2 to 10 microg. Pretreatment with MK-801 (5 or 10 microg, i.t.) significantly potentiated morphine antinociception by 49.9% or 38.7%, respectively. When rats were pretreated with MK-801, DM could not further enhance morphine antinociception (45.7% vs 50.5% and 43.3%).. Our results suggest that spinal NMDA receptors play an important role in the effect of DM to potentiate morphine antinociception.

Topics: Analgesics, Opioid; Animals; Dextromethorphan; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Synergism; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Morphine; Pain; Pain Measurement; Random Allocation; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

Opioids are effective topical analgesics in the radiant heat tailflick assay and display synergistic interactions with a number of other classes of drugs. To determine whether these actions extend to other types of nociception, we examined the actions of topical morphine and lidocaine in a tail formalin assay in the mouse. Formalin responses in the tail were similar to those seen in the hind paw, but were limited to licking. Unlike the traditional hind paw assay, the time-course of nociceptive behavior in the tail was monophasic; lasting 40-60 min. Morphine, MK-801 and acetylsalicylic acid (ASA) were active systemically in the tail formalin assay with potencies similar to those seen in the second phase of the paw formalin test. Both morphine and lidocaine were active topically in the tail formalin assay, although their time-course of action appeared to be shorter than that of the formalin. However, morphine displayed ceiling effect not seen when it was administered systemically. Lidocaine also had a ceiling effect. When given together, the response to the combination was supra-additive, consistent with our prior studies showing synergy in the radiant heat tailflick assay. These studies validate the formalin assay in the tail and support the topical actions of opioids and other drugs in a second pain model. They also suggest supra-additive interactions between morphine and lidocaine similar to those previously seen. The tail formalin assay will be valuable in assessing the activity of topical drugs.

Topics: Analgesics, Opioid; Anesthetics, Local; Animals; Anti-Inflammatory Agents, Non-Steroidal; Aspirin; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Lidocaine; Male; Mice; Mice, Inbred ICR; Morphine; Pain; Pain Measurement; Tail

Spinal cord dorsal horn N-methyl-D-aspartate (NMDA) receptors have been implicated in central sensitization, enhanced responsiveness to peripheral stimuli following peripheral injury. Since hyperalgesia is a behavioral consequence of central sensitization, it should be attenuated at the level of the dorsal horn with NMDA receptor antagonists. However, responsiveness to thermal and mechanical hyperalgesia may be distinct, and have thus far not been directly compared in chronic inflammatory pain models. In the present study, inflammation was induced with complete Freund's adjuvant (CFA) injected into the rat hind paw and NMDA receptor antagonists dizocilpine (MK-801) or 2-amino-5-phosphonovaleric acid (AP-5) were intrathecally injected in rats to determine the effects on both mechanical and thermal hyperalgesia. Locomotor tests and reflexes were also conducted to evaluate potential motor side effects. The NMDA receptor antagonists dose-dependently ameliorated mechanical hyperalgesia, but had marginal effects on thermal hyperalgesia. In ranges near antihyperalgesic doses, significant disruption of motor coordination was observed for both antagonists. These results suggest that, depending on the stimulus, NMDA receptors may have variable significance for central sensitization-mediated hyperalgesia, and that NMDA receptor antagonists may have therapeutic potential for some, but not all components in the clinical manifestation of inflammatory pain.

Topics: Animals; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Hyperalgesia; Inflammation; Injections, Spinal; Male; Motor Activity; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Treatment Outcome; Valine

The efficacy of spinally versus supraspinally administered morphine was studied in rats with a spinal nerve ligation-induced neuropathy. Behavioural assessment indicated that the effect of intrathecally administered morphine on pain-related responses was attenuated when compared with unoperated controls. The decreased efficacy of spinal morphine was associated with neuropathic symptoms, since sham ligation or nerve ligation without accompanying tactile allodynia did not lead to spinal inefficacy of morphine. In contrast, the pain attenuating effect of morphine in the periaqueductal gray (PAG) was enhanced in neuropathic animals. The effect of systemically administered morphine on pain-related behavior of neuropathic rats was in the same range as in controls or decreased, depending on the test. Coadministration of lidocaine or MK-801, a N-methyl-D-aspartate (NMDA) receptor antagonist, into the rostroventromedial medulla enhanced the tactile antiallodynic but not the thermal antinociceptive effect of intrathecally administered morphine in neuropathic animals. Supraspinal administration of MK-801 or lidocaine did not influence efficacy of spinal morphine in sham-operated animals. Electrophysiological recordings of nociceptive wide-dynamic range (WDR) neurons in the deep spinal dorsal horn of pentobarbitone-anesthetized animals corresponded to a large extent with behavioral results. The inhibitory effect of spinally and systemically administered morphine on WDR neuron responses was attenuated whereas that induced by morphine in the PAG was enhanced in neuropathic animals. The results indicate that in spinal nerve ligation-induced neuropathy the efficacy of spinal morphine is decreased whereas that of supraspinal morphine is increased. Descending influence from brainstem-spinal pathways, involving NMDA receptors in the rostroventromedial medulla, may contribute to the selective reduction in tactile antiallodynic efficacy of spinal morphine.

Topics: Analgesics, Opioid; Anesthetics, Local; Animals; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Electrophysiology; Excitatory Amino Acid Antagonists; Hyperalgesia; Injections, Spinal; Lidocaine; Ligation; Male; Medulla Oblongata; Morphine; Naloxone; Narcotic Antagonists; Neurons; Pain; Pain Measurement; Periaqueductal Gray; Physical Stimulation; Rats; Rats, Wistar; Reaction Time; Spinal Cord; Spinal Nerves; Time Factors

To explore the facilitation of nociceptive response by dynorphin (Dyn ) A in a model of formalin test in rats, the effects of single intrathecal injection (i.t.) of normal saline (NS), MK-801 (antagonist of NMDA receptor), naloxone (antagonist of opioid receptor), or Dyn A (1-17) were observed, and the effects of i.t. MK-801 or naloxone followed by i.t. Dyn A (1-17) were observed as well. The nociceptive licking and biting induced by injection of formalin exhibited two phases. The first phase lasted for a relatively short period of 3-9 min, and the second phase lasted for a relatively longer period after a 3 to 6- min quietness. The results showed that there were no differences in the first phase in all groups; however, there were differences in the second phase as follows: (1) the duration of nociceptive response was significantly increased in Dyn A (1-17) group (489.5+/-22.5 s) as compared to that of NS group (344.7+/-12.9 s), MK-801 group (331.4+/-20.7 s) or naloxone group (352.5+/-18.4 s) (P<0.01 in three cases); (2) the duration of nociceptive response was significantly shortened in MK-801 plus Dyn A (1-17) group (285.7+/-19.4 s) as compared to that of Dyn A (1-17) group (P<0.01), but there were no significant differences as compared to that of MK-801 group; and (3) there was no significant difference in the second phase between naloxone plus Dyn A (1-17) group (473.8+/-17.8 s) and Dyn A (1-17) group, but the duration of nociceptive response was longer than that of NS group or naloxone group (P<0.01 in both). The results obtained suggest: (1) at the spinal cord, Dyn A (1-17) facilitates nociceptive responses; (2) NMDA receptors, but not opioid receptors, are possibly involved in the nociception by Dyn A (1-17).

Topics: Animals; Dizocilpine Maleate; Dynorphins; Formaldehyde; Injections, Spinal; Naloxone; Nociceptors; Pain; Rats; Receptors, N-Methyl-D-Aspartate

Although the antinociceptive effect of NMDA antagonists in the formalin test is well recognised, these compounds can induce adverse motor effects. The aim of this study was to identify the systemic doses of NMDA antagonists that induce analgesia without causing side effects. Male Swiss mice (30-40g) received a subcutaneous (sc) injection of 1.25% formalin (50 micro l) in the dorsal surface of the right hind-paw and, 15min before or after formalin, an ip injection of one of the following NMDA receptor antagonists: MK 801 (0.01, 0.025, and 0.05mg/kg), memantine (0.1, 0.5, and 1mg/kg), ketamine (0.125, 0.25, and 0.5mg/kg), dextromethorphan (5, 10, and 20mg/kg), and CGP 37849 (4, 6, and 8mg/kg). Pain-related behaviour (licking, lifting, favouring, shaking, and flinching of the treated paw) was recorded at 5-min intervals for 60min. The NMDA receptor antagonists significantly (p<0.01) and dose-dependently reduced, versus controls, nociceptive activity during the second phase of the formalin test (from the 20th to the 60thmin): at the highest doses, 97.6+/-0.1% with MK 801; 90.4+/-0.2% with memantine; 74.7+/-0.3% with ketamine; 92.8+/-0.4% with dextromethorphan; and 80.7+/-0.3% with CGP 37849, without affecting coordination. The rank order potency of antinociceptive activity of NMDA antagonists was: MK801>memantine>ketamine>dextromethorphan>CGP37849. The NMDA antagonists administered after formalin (during the analgesic interval) did not affect the late phase of the formalin test. In conclusion, systemic administration of NMDA receptor antagonists decreases the nociception observed during the late phase of the formalin test.

Topics: Animals; Behavior, Animal; Dextromethorphan; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Formaldehyde; Injections, Intraperitoneal; Ketamine; Male; Memantine; Mice; Nociceptors; Pain

Activation of spinal cord dorsal horn ionotropic glutamate receptors leads to pain-related behaviors. However, the role of spinal metabotropic glutamate receptors (mGlu), particularly the mGlu5 receptor subtype, in nociception has not been well characterized. A recently described subtype selective and potent mGluR5 antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP) was used to evaluate the role of the mGlu5 receptor in cold sensitivity. Intrathecal (i.t.) injection of group I (mGlu1 and mGlu5 receptors) mGlu receptor-selective agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) increased the hind paw frequency and duration of lifting of rats placed on a cold (4 degrees C) surface, a behavior similarly observed in rats with a chronic constriction injury (CCI) of the sciatic nerve. In contrast, rats i.t. injected with DHPG did not display increased lifting when placed on a room temperature surface. I.t. injection of MPEP before i.t. injection of DHPG blocked DHPG-evoked cold hypersensitivity, suggesting that activation of spinal mGlu5 receptors induces this behavioral response. In contrast, i.t. injection of MPEP after i.t. injection of DHPG had no effect. In addition, i.t. injection of MPEP did not affect cold hypersensitivity in rats with a CCI. These data suggest that acute activation of spinal cord mGlu5 receptors results in increased sensitivity to cold, but ongoing cold hypersensitivity does not involve activation of the mGlu5 receptor.

Topics: Animals; Behavior, Animal; Cold Temperature; Constriction, Pathologic; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Methoxyhydroxyphenylglycol; Pain; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Sciatic Nerve; Spinal Cord

Phosphorylation of a subunit of N-methyl-D-aspartate (NMDA) receptor by protein tyrosine kinase (PTK) Src or Trk is known to enhance its channel activity. We examined whether a spinally administered selective PTK inhibitor, lavendustin A, which has high affinity for Src and Trk tyrosine kinases, could influence the development and maintenance of inflammatory hyperalgesia or NMDA-induced hyperalgesia. Inflammation was induced by injection of a mixture of carrageenan and kaolin into the tail base of rats. In another group of rats, hyperalgesia was induced by intrathecal administration of NMDA. Intrathecal administration of lavendustin A (1.0 microg) or NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptane-5,10-iminemaleate, MK-801 (3.0 microg) before injection of a mixture of carrageenan and kaolin or after the development of inflammation inhibited carrageenan-kaolin-induced mechanical hyperalgesia. Intrathecal injection of 1.0 microg NMDA produced thermal and mechanical hyperalgesia. Co-administration of 1.0 microg lavendustin A with NMDA significantly reduced the duration of spontaneous pain behaviour and inhibited NMDA-induced hyperalgesia. Lavendustin A itself did not cause any sedation, motor impairment or analgesia. Our results suggest that inhibition of PTK could be therapeutically effective as an analgesic in some NMDA receptor-mediated hyperalgesic states.

Topics: Animals; Carrageenan; Dizocilpine Maleate; Hot Temperature; Hyperalgesia; Inflammation; Injections, Spinal; Kaolin; Male; N-Methylaspartate; Pain; Pain Measurement; Phenols; Protein-Tyrosine Kinases; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

The steady-state mRNA levels of the NMDA receptor NR1 subunit were determined by a quantitative solution hybridization assay in selected CNS regions associated with antinociception in the rat. Tissues were obtained by microdissection from rats treated chronically with morphine alone or in combination with LY274614, a competitive NMDA receptor antagonist. Morphine treatment for 7 days resulted in the development of tolerance to morphine's analgesic effect and produced a significant decrease in the steady-state NR1 mRNA levels in the spinal cord dorsal horn (by 16%), and an elevation in nucleus raphe magnus and medial thalamus (by 26 and 38%, respectively). The NR1 mRNA levels were unchanged in the lateral paragigantocellular nucleus, locus coeruleus, periaqueductal grey, and sensorimotor cortex. NMDA receptor binding in the spinal cord measured with [3H]MK-801 was reduced approximately 50% by chronic morphine treatment. Co-administration of LY274614 (s.c. at 24 mg/kg/24 h via an osmotic pump) not only attenuated the development of morphine tolerance but also prevented the changes in the NR1 mRNA levels induced by chronic morphine administration. Neither a 7-day infusion of LY274614 nor an acute injection of morphine (10 mg/kg, s.c.) changed the NR1 mRNA levels. These results suggest that changes in the expression of the NR1 mRNA induced by chronic morphine in three CNS regions involved in antinociception are associated with the development of morphine tolerance and in the spinal cord, morphine tolerance is associated with the downregulation of NMDA receptors.

Topics: Animals; Binding, Competitive; Central Nervous System; Dizocilpine Maleate; Down-Regulation; Drug Administration Schedule; Drug Interactions; Drug Tolerance; Excitatory Amino Acid Antagonists; Isoquinolines; Male; Morphine; Neurons; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; RNA, Messenger

Topically administered capsaicin produces thermal allodynia, and this effect has been used to investigate pain transduction and its pharmacological modulation. This study investigated the parameters of topical capsaicin-induced thermal allodynia in unanesthetized rhesus monkeys and its pharmacological modulation by centrally acting compounds [a kappa-opioid agonist: (5alpha,7alpha,8beta)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro [4.5]dec-8-yl)-benzeneacetamide (U69,593); and noncompetitive N-methyl-d-aspartate (NMDA) antagonists: ketamine and MK-801 (dizocilpine)]. Rhesus monkeys (n = 4) were studied within the warm water tail withdrawal assay (20-s maximum latency), using thermal stimuli that are normally not noxious (38 and 42 degrees C). Capsaicin was applied topically on the tail (0.0013 and 0.004 M capsaicin solution on a 1-cm2 patch; 15-min contact). Topical capsaicin produced concentration-dependent thermal allodynia in both temperatures, robustly detected 15 to 90 min after topical capsaicin removal. A similar allodynic profile was observed with topical administration of the "endovanilloid" N-arachidonoyl-dopamine. The kappa-agonist U69,593 (0.01-0.1 mg/kg, s.c.) dose dependently prevented capsaicin (0.004 M)-induced allodynia in 38 and 42 degrees C, and the largest U69,593 dose also reversed ongoing allodynia within this model. Two NMDA antagonists, ketamine and MK-801 (0.32-1.8 and 0.032-0.056 mg/kg, respectively), also prevented capsaicin-induced allodynia in 38 degrees C, but only variably in 42 degrees C, at doses that did not cause robust thermal antinociceptive effects. At the largest doses studied, ketamine but not MK-801 also briefly reversed ongoing capsaicin-induced allodynia. The present model of topical capsaicin administration may be used to study antiallodynic effects of opioid and nonopioid compounds, as well as their ability to prevent and reverse allodynia, in unanesthetized nonhuman primates in the absence of tissue disruption.

Topics: Aminobutyrates; Analgesics; Animals; Benzeneacetamides; Capsaicin; Disease Models, Animal; Dizocilpine Maleate; Dynorphins; Female; Ketamine; Macaca mulatta; Pain; Pain Measurement; Peptide Fragments; Pyrrolidines

In the rat, antinociception of supraspinal origin is observed in response to administration of cocaine or an antagonist of the NMDA receptor for glutamate. The current study was conducted to determine if endocannabinoids are involved in the antinociceptive effect of cocaine, or antagonism of NMDA receptor binding. Intraperitoneal (i.p.) administration to male rats of cocaine, or the NMDA receptor antagonist, MK-801, resulted in a significant antinociceptive response of supraspinal origin, as indicated by a significant increase in reaction time in the hot plate test of analgesia (increase in the amount of time before the animal reacted to the hot plate by licking its paws or jumping). Treatment with SR141716A, a specific antagonist of the cannabinoid (CB1) receptor, resulted in a complete reversal of cocaine-induced antinociception when administered at a dose of 5.0mg/kg. Although the 2.5 and 5.0mg/kg doses of SR141716A produced a significant reduction in the antinociceptive effect of MK-801, the effect was incomplete since the reaction time in the hot plate test remained greater than that observed in vehicle-treated controls. These findings suggest that activation of the CB1 receptor participates significantly in antinociception resulting from treatment with cocaine and with the NMDA receptor antagonist, MK-801. The partial reversal of the antinociceptive effect of MK-801 by CB1 receptor antagonism indicates other mediators of nociception, in addition to the endocannabinoids, appear to be active in the antinociceptive response to NMDA receptor antagonism.

Topics: Anesthetics, Local; Animals; Cannabinoid Receptor Modulators; Cocaine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Male; Pain; Pain Measurement; Piperidines; Pyrazoles; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Cannabinoid; Receptors, Drug; Receptors, N-Methyl-D-Aspartate; Rimonabant

Contribution of peripheral NMDA receptors in craniofacial muscle nociception and inflammation was examined. Nocifensive paw-shaking behavior following masseteric injection of mustard oil (MO) was quantified in lightly anesthetized rats. MK-801 (0.3 mg/kg) preadministered in the masseter muscle significantly reduced the peak and overall magnitude of the MO-induced noficensive behavior. The reduction was greater than that produced by the same dose of MK-801 given intravenously or in the biceps muscle. Rats were sacrificed 2 h later and masseter muscles dissected and weighed. The injected muscle was 27.29+/-6.7% heavier than the contralateral muscle. The weight difference was significantly less only in rats pretreated with masseteric MK-801. These data provide evidence that peripheral NMDA receptors play an important role in craniofacial muscle nociception and inflammation.

Topics: Animals; Dizocilpine Maleate; Edema; Excitatory Amino Acid Antagonists; Male; Masseter Muscle; Mustard Plant; Nociceptors; Pain; Plant Extracts; Plant Oils; Rats; Receptors, N-Methyl-D-Aspartate

The mesocorticolimbic circuitry has been implicated in the pathophysiology of several neuropsychiatric syndromes like chronic pain and addiction. The aim of this study was to evaluate the effects of dizocilpine (MK-801), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, on sensorimotor behaviors and the consequent changes in the dopamine, glutamate, and opiate systems in rats. Five groups of rats were subjected to acute tests for nociception (hot plate and paw pressure) before and after MK-801 (0.05, 0.1, 0.2 and 0.4 mg/kg, i.p.) or saline. Another two groups received daily i.p. saline or MK-801 (0.4 mg/kg) for 15 days. The nociceptive tests were performed on days 1, 7, and 14. On day 15 the rats received the last injection and were immediately sacrificed. We measured the mRNA expression, by in situ hybridization (ISH), of various dopamine and glutamate receptors, and enkephalin (Enk), dynorphin (Dyn), and substance P (SP) in the striatum, nucleus accumbens (NAC), piriform and cingulate cortex. Acute MK-801, dose-dependently, resulted in hyperalgesia. The chronic effects of 0.4 mg/kg MK-801 showed an extinction of the acute hyperalgesic effects especially with the hot plate test. The ISH studies revealed a decrease in mRNA expression of Enk and SP in the striatum and NAC. Our results indicate that the reversal of acute MK-801-induced hyperalgesia, with repeated exposure to systemic MK-801, is not directly related to changes in dopamine and glutamate receptors and might involve alteration of the striatal neuropeptide system.

Topics: Animals; Autoradiography; Behavior, Animal; Brain; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Hyperalgesia; In Situ Hybridization; Locomotion; Male; Neuropeptides; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Dopamine; Receptors, Glutamate; RNA, Messenger; Stereotyped Behavior; Time Factors

Based on our previous findings that glutamate microinjected into the thalamic nucleus submedius (Sm) inhibits dose-dependently the rat tail-flick (TF) reflex, this study investigated which glutamate receptor subtype is involved in mediating this effect. The effects of an NMDA (N-methyl-D-aspartate), non-NMDA or metabotropic glutamate receptor (mGluR) antagonist microinjected into Sm on the TF reflex were examined in untreated or in Sm glutamate treated (microinjection into the Sm) rats. The TF latencies were measured in each of these groups of rats every 5 min. Injection of DNQX [6,7-dinitroquinoxaline-2,3(1H,4H)-dione], a non-NMDA receptor antagonist, or (+/-)-MCPG [(+/-)-alpha-methyl-4-carboxyphenylglycine], a mGluR antagonist, into the Sm blocked the inhibitory effects induced by a subsequent microinjection of glutamate into the same Sm site. The TF latency increased only by 6.6+/-1.6 or 9.0+/-1.1%, respectively, of the baseline value, which was markedly less than that (51.3+/-8.4 or 50.7+/-5.3%) obtained from injection of glutamate only (P<0.001, n=8). However, pre-microinjection of MK-801 [(+)-5-methyl-10,11-dibenzo[a,d]cyclohepten-5,10-imine], an NMDA receptor antagonist, into the Sm had no effect on the Sm glutamate-evoked inhibition of the TF reflex. The TF latency change (40.0+/-11.1%) was not significantly different (P>0.05, n=8) compared with that obtained from glutamate injection alone. These observations suggest that non-NMDA and metabotropic glutamate receptors, but not NMDA receptors, are involved in mediating Sm glutamate-evoked antinociception.

Topics: Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; Male; Microinjections; Pain; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Thalamus

We investigated the involvement of N-methyl-D-aspartate (NMDA) glutamate receptor in the expression of the proteins Zif/268 and c-Fos elicited by painful stimuli. To this purpose, the effect of the administration of MK-801, an NMDA receptor antagonist, on Zif/268 and c-Fos expression following a noxious stimulus, represented by formalin injection into the whisker pad of rats, was examined in neurons of the trigeminal nucleus caudalis. Furthermore, the co-localization of formalin injection-evoked Zif/268 and c-Fos expression and subunit 1 of the NMDA receptor (NR1) was studied in this nucleus. Zif/268 or c-Fos immunoreactivity elicited by formalin injection was significantly reduced by pretreatment with MK-801 in the superficial layer of the trigeminal nucleus caudalis; more than 40% of the neurons expressing Zif/268 and c-Fos in this layer were also immunolabeled by NR1. On the other hand, there was little effect of MK-801 administration on Zif/268 and c-Fos immunoreactivity in the nucleus proprius and deep lamina V of the trigeminal nucleus caudalis, while most neurons expressing Zif/268 or c-Fos in these two regions were labeled by NR1. These results point out differences between the superficial and deeper layers of the trigeminal nucleus caudalis in the involvement of NMDA receptor in the mechanisms underlying the expression of protein products of immediate early genes induced by painful stimuli.

Topics: Animals; Cell Count; Disease Models, Animal; Dizocilpine Maleate; DNA-Binding Proteins; Early Growth Response Protein 1; Excitatory Amino Acid Antagonists; Formaldehyde; Immediate-Early Proteins; Immunohistochemistry; Male; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Transcription Factors; Trigeminal Nuclei; Vibrissae

To determine whether both the N-methyl-D-aspartate (NMDA) and non-NMDA receptors in the knee joint contribute to the induction and/or maintenance of arthritic pain, we examined the effects of intra-articular injection of NMDA receptor antagonist dizocilpine (MK-801) and non-NMDA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline (NBQX) on the decrease in weight load induced by carrageenan injection into the knee joint cavity in rats. Injection of MK-801 (0.75 and 1.5 mM) and NBQX (0.25, 0.625 and 2.5 mM) immediately prior to carrageenan injection (2%, 40 microl) significantly prevented the pain-related behavior. However, injection of MK-801 (0.75 and 1.5 mM) and NBQX (0.625 and 2.5 mM) 5 h after carrageenan injection had no effect on pain-related behavior. These results suggest that both the NMDA and non-NMDA receptors in the knee joint are involved in the induction, but not maintenance, of arthritic pain.

Topics: Animals; Arthritis, Experimental; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Joints; Male; Pain; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Time Factors

In the present three-part study, the effects of intrathecally administered N-methyl-D-aspartate (NMDA) receptor antagonists on responses to noxious and innocuous colorectal distention (CRD) were examined. In the first part, a passive-avoidance paradigm was used to confirm that 80 mm Hg CRD is a noxious stimulus since it produced avoidance behavior. Acquisition of this behavior was blocked by the NMDA receptor antagonist D(-)-2-amino-5-phosphonopetanoic acid (APV, 60 nmol, intrathecal). In contrast, 20 mm Hg CRD is an innocuous stimulus since there was no difference in the behavior of these animals compared to nondistended controls. In the second part, the effects of the NMDA receptor antagonist dizocilpine maleate (MK-801, 0-100 nmol, intrathecal) on CRD-induced Fos expression in the lumbosacral spinal cord were examined. Noxious and innocuous CRD induced 98+/-4 and 50+/-2 Fos labeled cells per section per side of the spinal cord, respectively. MK-801 dose-dependently attenuated noxious CRD-induced Fos. Compared to saline, the peak attenuation was 55%. Innocuous CRD-induced Fos was attenuated by 36% following 100 nmol MK-801. In the third part, the effects of APV (0-240 nmol, intrathecal) on the visceromotor reflex were examined. APV dose-dependently attenuated the visceromotor reflex to graded intensities of CRD that went from the innocuous into the noxious range. In separate animals that only received innocuous stimulation, APV dose-dependently attenuated the visceromotor reflex. The magnitude of attenuation was similar for both stimulus paradigms. These data expand upon our previous dorsal horn neuronal recordings which showed that spinal NMDA receptors partially mediate the processing of both noxious and innocuous colorectal stimuli. They further underscore a difference from somatic tissue in the role of NMDA receptors in processing acute or transient visceral stimuli in the absence of tissue injury.

Topics: 2-Amino-5-phosphonovalerate; Animals; Behavior, Animal; Colon; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Rectum; Reflex; Spinal Cord; Visceral Afferents

The role of N-methyl-D-aspartate (NMDA) receptors in supraspinal and spinal sites on the reduction of supraspinal micro-opioid receptor-induced antinociception in diabetic mice was examined. The antinociceptive effect of i.c.v. [D-Ala(2), N-MePhe(4), Gly-ol(5)]enkephalin (DAMGO, 20 pmol) in diabetic mice was significantly less than that in non-diabetic mice. The antinociceptive effect of i.c.v. DAMGO (20 pmol) was significantly and dose dependently reduced by i.c.v. (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) in both non-diabetic (0.03-0.3 nmol) and diabetic mice (0.1-3.0 nmol). While the antinociceptive effect of i.c.v. DAMGO (10 pmol) was significantly enhanced by i.c.v NMDA (0.01-0.1 nmol) in non-diabetic mice, the same doses of i.c.v. NMDA had no significant effect on the antinociceptive effect of i.c.v. DAMGO (20 pmol) in diabetic mice. In non-diabetic mice, the antinociceptive effect of DAMGO (20 pmol, i.c.v.) was dose dependently reduced by intrathecal administration of MK-801 (0.1-1.0 nmol). The antinociceptive effect of DAMGO (20 pmol, i.c.v.) was dose-dependently enhanced by MK-801 (0.1-1.0 nmol, i.t.) in diabetic mice. Furthermore, NMDA (0.1 nmol, i.t.) significantly enhanced the antinociceptive effect of DAMGO (10 pmol, i.c.v.) in non-diabetic mice. However, in non-diabetic mice, the antinociceptive effect of DAMGO (40 pmol, i.c.v.) was dose dependently reduced by NMDA (0.03-0.3 nmol, i.t.). These results suggest that NMDA receptor function in supraspinal and spinal sites appear to be modulated differently by the diabetic state, and this functional modulation may play an important role in the reduction of supraspinal micro-opioid receptor-induced antinociception in diabetic animals.

Topics: Animals; Diabetes Mellitus, Experimental; Dizocilpine Maleate; Drug Interactions; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Injections, Intraventricular; Male; Mice; Mice, Inbred ICR; Pain; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu

We previously showed that the intraperitoneal (i.p.) administration of 200mg/kg cyclophosphamide, an antitumoral agent, modified the behaviour of rats with cystitis induced by acrolein, a toxic urinary by-product of cyclophosphamide. This behaviour, (namely decreased breathing rate, closing of the eyes, and specific postures), was scored to indirectly assess the nociception elicited by the cystitis and to use this experimental model as a vesical pain model. Here we investigated the involvement of the N-methyl-D-aspartate (NMDA) receptors and thus of the excitatory amino acid system in this model. We administered dizocilpine (0.01 to 0.1mg/kg intravenously (i.v.) and 1 to 20 microg/rat intrathecally (i.t.)) and ketamine (5 and 10mg/kg i.v. and 50 to 1000 microg/rat i.t.), two non-competitive NMDA receptor antagonists that bind to the channel site, and AP-5 (0.01 to 1mg/kg i.v. and 20 to 500 microg/rat i.t), a competitive antagonist that binds to the glutamate site. Whichever the route of administration (i.v. or i.t.), dizocilpine dose-relatedly reduced the behavioural disorders induced by cyclophosphamide. Systemic ketamine also dose-dependently, though transiently, reduced the effects of cyclophosphamide, but ketamine i.t. and AP-5 i.v. and i.t. did not induce any reduction of these effects.These results (i) demonstrate that in the cyclophosphamide-induced vesical pain model NMDA receptors are involved in the nociception, as shown by the effects of dizocilpine and systemic ketamine, (ii) reveal marked differences in the data obtained with various NMDA receptor antagonists, possibly due to their physicochemical properties, to the animal pain model used, to the noxious stimulus applied or to any combination of these factors.

Topics: Acrolein; Animals; Antineoplastic Agents, Alkylating; Behavior, Animal; Cyclophosphamide; Cystitis; Dizocilpine Maleate; Dose-Response Relationship, Drug; Injections, Intravenous; Injections, Spinal; Ketamine; Male; Models, Animal; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Recent studies demonstrate the possible existence of tonic modulatory control of nociceptive input mediated by spinal cannabinoid receptors (CB1). Accordingly, it is predicted that a reduction in the spinal CB1 receptors may enhance sensitivity to sensory stimuli and a decrease in spinal antinociceptive potency to cannabinoid agonists. An antisense oligodeoxynucleotide (ODN) specific to the CB1 receptor was used to 'knock-down' CB1 receptors in the lumbar spinal cord and dorsal root ganglia by the local, repeated intrathecal (i.th.) administration of the ODN. This treatment resulted in a decrease in lumbar spinal CB1 receptor expression accompanied by a decrease in the response thresholds to both innocuous tactile and noxious thermal stimuli. The antinociceptive action of the CB1 agonist, WIN 55,212-2, by i.th. administration was also significantly attenuated after treatment with the antisense ODN. Similar treatment using a mismatch control ODN had no effect on receptor protein or on sensory thresholds. The effects of the antisense ODN treatment on sensory thresholds were fully reversed after discontinuation of the ODN injection. The antisense ODN treated rats also showed a significant increase in lumbar spinal dynorphin A. Acute i.th. injection of MK-801 or an antidynorphin antiserum blocked the antisense ODN-induced tactile and thermal hypersensitivity. These data support the possibility of endogenous inhibitory cannabinoid tone to limit spinal afferent input of thermal and tactile stimuli. Lifting of this inhibitory tone through a 'knock-down' of spinal CB1 receptors apparently lowers the thresholds for sensory input, as reflected by the actions of MK-801 to block tactile and thermal hypersensitivity. The increased spinal dynorphin may act to further promote afferent outflow and abnormal pain because sequestration of spinal dynorphin with antiserum also reverses the manifestations of abnormal pain following knock-down of CB1 receptors.

Topics: Analgesics; Animals; Antibodies; Benzoxazines; Cyclohexanols; Dizocilpine Maleate; Dynorphins; Excitatory Amino Acid Antagonists; Male; Mice; Mice, Inbred ICR; Morpholines; Naphthalenes; Oligodeoxyribonucleotides, Antisense; Pain; Receptors, Cannabinoid; Receptors, Drug; Spinal Cord; Tritium

The N-methyl-D-aspartate (NMDA) antagonist ifenprodil and several structurally related compounds are highly selective for the NR2B-containing receptor subtype. This selectivity could provide an explanation for the reported difference of the analgesic and side-effect profile of ifenprodil-like compounds from other NMDA antagonists. In this work, we have queried if the ifenprodil-induced antinociception can be attributed to the block of NMDA receptors in the spinal cord. Ifenprodil and some other NMDA antagonists (MK-801, memantine) were tested in a model of inflammatory pain (Randall-Selitto) in rats. The in vivo NMDA antagonism was assessed in anaesthetised rats on responses of spinal dorsal horn (DH) neurones to iontophoretic NMDA and in the model of single motor unit (SMU) wind-up. Ifenprodil, MK-801 and memantine dose-dependently increased nociceptive thresholds in the Randall-Selitto model. Antinociceptive doses of the channel blockers selectively antagonised NMDA responses of DH neurones and inhibited wind-up. In contrast, antinociceptive doses of ifenprodil did not show any NMDA antagonism in electrophysiological tests. Although ifenprodil did not inhibit the SMU responses to noxious stimuli in spinalised rats, it markedly and dose-dependently inhibited nociceptive SMU responses in sham-spinalised rats. These results argue against the spinal cord being the principal site of antinociceptive action of ifenprodil; supraspinal structures seem to be involved in this effect.

Topics: Analgesics; Animals; Decerebrate State; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Male; Memantine; Motor Activity; N-Methylaspartate; Naloxone; Narcotic Antagonists; Pain; Piperidines; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

Selective ligation of the L5/L6 spinal nerves produces a partial denervation of the hindpaw and has proved to be a useful model for studying the mechanisms underlying neuropathic pain. Two weeks after surgery, in vivo electrophysiological studies were performed in sham operated and nerve injured rats and the responses of spinal dorsal horn neurones to controlled electrical and natural (mechanical and heat) stimuli were recorded. The systemic effects of three N-methyl-D-aspartate receptor (NMDA) antagonists, ketamine (1-10 mg/kg), memantine (1-20 mg/kg) and MK-801 (0.1-5 mg/kg) were compared. Ketamine a clinically available NMDA receptor antagonist, produced greater reductions of the postdischarge, thermal (10 mg/kg, P=0.02), and mechanical evoked responses in spinal nerve ligated (SNL) rats (von Frey 9 g, 1 mg/kg, P=0.04; 5 mg/kg, P=0.01; 10 mg/kg, P=0.05; von Frey 50 g, 5 mg/kg, P=0.02; 10 mg/kg, P=0.003). The inhibition of wind-up was comparable in both animal groups. Memantine produced powerful inhibitions of wind-up after nerve injury with little effect in sham controls (5 mg/kg, P=0.02). The postdischarge, mechanical and thermal evoked responses were reduced to similar extents by memantine in both experimental groups. The effects of MK-801 were comparable between SNL and sham operated rats for all neuronal measures (wind-up, postdischarge, thermal and noxious mechanical evoked responses). The differential blocking abilities of these antagonists on the various neuronal responses may relate to the characteristics of their voltage-dependent blockage of the channel associated with the receptor. The favourable side effect profile of memantine supports its potential use for the treatment of neuropathic pain.

Topics: Animals; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Excitatory Amino Acid Antagonists; Hot Temperature; Ketamine; Ligation; Male; Memantine; Neurons; Pain; Peripheral Nervous System Diseases; Physical Stimulation; Rats; Rats, Sprague-Dawley; Spinal Cord; Spinal Nerves

The spinal processing by which intra-arterial injection of capsaicin (CAP) induces vocalization response (VOR) was investigated in guinea pigs. Intrathecal pre-treatment with CP-96,345 (a selective NK(1) receptor antagonist, 50 nmol) did not affect the CAP-induced VOR. However, significant attenuation of the VOR was observed by intrathecal pre-treatment with a selective NK(2) receptor antagonist MEN-10,376 (40 nmol) accompanied with a significant change in the response modality. MK-801 [an N-methyl-D-aspartate (NMDA) receptor antagonist, 20 and 40 nmol] inhibited the CAP-induced VOR dose-dependently without affecting the response modalities. Furthermore, intrathecal co-treatment with 40-nmol MEN-10,376 and 40-nmol MK-801 resulted in a marked inhibitory effect on the VOR followed by a significant alteration of response modalities. Intrathecal pre-treatment with neurokinin A (NKA; a tachykinin NK(2) receptor agonist, 1 nmol) enhanced the CAP-induced VOR. These behavioral results suggested that spinal NK(2) and NMDA receptors might have priority over NK(1) receptors in the spinal processing of nociceptive information from the CAP-sensitive nociceptor.

Topics: Animals; Avoidance Learning; Biphenyl Compounds; Capsaicin; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Femoral Artery; Guinea Pigs; Hindlimb; Injections, Intra-Arterial; Male; Neurokinin A; Nociceptors; Pain; Peptide Fragments; Receptors, N-Methyl-D-Aspartate; Receptors, Neurokinin-2; Spinal Cord; Vocalization, Animal

The purpose of this study was to determine whether ES-242-1, a novel N-methyl-D-aspartate (NMDA) receptor antagonist of microbial origin, has anti-nociception at the spinal level and to evaluate how its anti-nociceptive effect differs from that of MK-801, a non-competitive NMDA receptor antagonist. Agents were injected intrathecally (0.1, 1.0 and 10 microg) through a previously implanted PE tube in rats. Formalin (2%, 100 microl) was injected subcutaneously into the left hindpaw 15 min after each antagonist administration. Licking time as a nociceptive behavior was measured in three stages after formalin-injection, such as early phase (0-9 min), late first phase (10-29 min) and late second phase (30-60 min). In the early phase, the largest dose of ES-242-1 significantly decreased total licking time, although MK-801 did not show any significant reduction. With the treatment of 1.0 and 10 microg MK-801, total licking time in both late first and second phases was significantly suppressed, although the smallest dose (0.1 microg) of ES-242-1 showed a significant reduction in the late second phase. These results indicate that ES-242-1 is highly effective against tonic pain, such as inflammatory pain.

Topics: Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Nociceptors; Pain; Pain Measurement; Pain Threshold; Pyrans; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Time Factors

Using NADPH-d histochemistry, the effect of NMDA receptor antagonist MK-801 on the expression of nitric oxide synthase (NOS) in the dorsal horn of the spinal cord was investigated during inflammatory pain and hyperalgesia induced by injection of formalin into the right hind paw. The course of the change in the nitric oxide (NO) content of the lumbar intumescence was observed by measuring the ratio of nitrate/nitrite (NO3T/NO2T) and also the end product of NO. The results showed that the NOS expression and NO contents significantly increased 24 h after formalin injection, which were substantially inhibited when MK-801 was intrathecally injected 15 min prior to formalin injection or 12 h after formalin injection. The results suggest that the increases in the expression of NOS and NO contents in the dorsal horn of the spinal cord are mediated by activation of NMDA receptors during pain and hyperalgesia after formalin injection.

Topics: Animals; Dizocilpine Maleate; Female; Hyperalgesia; Male; Nitric Oxide; Nitric Oxide Synthase; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

The intrathecal injection of fenvalerate, a sodium channel activator, at doses of 0.01 to 3 microg, dose-dependently induced the duration of a characteristic behavioral syndrome mainly consisting of reciprocal hind limb scratching directed towards caudal parts of the body and biting or licking of the hind legs in mice. Fenvalerate-induced behavior was inhibited by morphine (1-10 mg/kg, i.p.). The characteristic behavior was also inhibited by mexiletine, a sodium channel blocker; MK-801, a N-methyl-D-aspartate ion-channel blocker; and GR82334, a neurokinin-1-receptor antagonist. Calphostin C (3 pmol, i.t.), a protein kinase C inhibitor, inhibited fenvalerate-induced behavior. On the other hand, phorbol-12, 13-dibutyrate (50 pmol, i.t.), a protein kinase C activator, markedly enhanced the fenvalerate-induced behavior. The present results also showed that fenvalerate produced thermal allodynia and hyperalgesia in the tail-flick test. Furthermore, fenvalerate-induced thermal allodynia and hyperalgesia were inhibited by the pretreatment with calphostin C. These results suggest that the intrathecal administration of fenvalerate induces a marked nociceptive response and thermal allodynia/hyperalgesia, and they suggest that tetrodotoxin-resistant sodium channels may play an important role in this effect.

Topics: Animals; Behavior, Animal; Dizocilpine Maleate; Enzyme Activators; Enzyme Inhibitors; Hyperalgesia; Injections, Spinal; Male; Mexiletine; Mice; Mice, Inbred ICR; Nitriles; Pain; Physalaemin; Protein Kinase C; Pyrethrins

We investigated the effect of topical application of capsaicin cream on withdrawal latency in the hind foot of rat in response to radiant heat in an experimental model of neuropathic pain. A neuropathic state was induced by loose ligation of the sciatic nerve with chromic gut suture. A marked thermal hyperalgesia was observed in response to heat stimulus applied to the operated side from 3 days through 2 weeks, followed by a gradual return to the control level by 35 days after surgery. Capsaicin cream applied to both the bilateral hind instep and sole once a day for a continuous period of 2 weeks or 4 weeks alleviated thermal hyperalgesia in a dose-dependent manner. A remarkable effect was observed 2 weeks after the start of the application and this effect proved to be reversible. On the other hand, in sham-operated animals when capsaicin cream was applied once daily from day 7 after the sham operation, from 1 day through 3 weeks following capsaicin application, withdrawal latency of the sham-operated paws of the capsaicin-treated group was significantly increased as compared to that of the vehicle cream-treated group. The effects of antagonists of glutamate receptor and tachykinin receptors were investigated 7 days post surgery. Pretreatment with MK-801 (0.5 mg kg(-1), i.p.), but not with CNQX (0.5 mg kg(-1), i.p.), reversed the thermal hyperalgesia following nerve injury. Neither of RP67580 (1--10 mg kg(-1), i.p.) nor SR48968 (1--10 mg kg(-1), i.p.) had any effect on the withdrawal latency in the injured and non-injured hind paw. These results suggest that although the manifestation of effectiveness may be delayed by changes in networks of neurotransmitters related to the nociceptive pathways following nerve injury, longer-term repetitive application of capsaicin cream has a significant therapeutic effect on subjects with painful peripheral neuropathy.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Analgesics; Animals; Benzamides; Capsaicin; Carrageenan; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hyperalgesia; Indoles; Isoindoles; Male; Neuroprotective Agents; Pain; Peripheral Nervous System Diseases; Piperidines; Postoperative Period; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Substance Withdrawal Syndrome; Time Factors

Several lines of evidence have shown a role for the nitric oxide/cyclic guanosine monophosphate signaling pathway in the development of spinal hyperalgesia. However, the roles of effectors for cyclic guanosine monophosphate are not fully understood in the processing of pain in the spinal cord. The present study showed that cyclic guanosine monophosphate-dependent protein kinase Ialpha but not Ibeta was localized in the neuronal bodies and processes, and was distributed primarily in the superficial laminae of the spinal cord. Intrathecal administration of a selective inhibitor of cyclic guanosine monophosphate-dependent protein kinase Ialpha, Rp-8-[(4-chlorophenyl)thio]-cGMPS triethylamine, produced a significant antinociception demonstrated by the decrease in the number of flinches and shakes in the formalin test. This was accompanied by a marked reduction in formalin-induced c-fos expression in the spinal dorsal horn. Moreover, cyclic guanosine monophosphate-dependent protein kinase Ialpha protein expression was dramatically increased in the lumbar spinal cord 96 h after injection of formalin into a hindpaw, which occurred mainly in the superficial laminae on the ipsilateral side of a formalin-injected hindpaw. This up-regulation of cyclic guanosine monophosphate-dependent protein kinase Ialpha expression was completely blocked not only by a neuronal nitric oxide synthase inhibitor, 7-nitroindazole, and a soluble guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, but also by an N-methyl-D-aspartate receptor antagonist, dizocilpine maleate (MK-801). The present results indicate that noxious stimulation not only initially activates but also later up-regulates cyclic guanosine monophosphate-dependent protein kinase Ialpha expression in the superficial laminae via an N-methyl-D-aspartate-nitric oxide-cyclic guanosine monophosphate signaling pathway, suggesting that cyclic guanosine monophosphate-dependent protein kinase Ialpha may play an important role in the central mechanism of formalin-induced inflammatory hyperalgesia in the spinal cord.

Topics: Animals; Antibodies; Behavior, Animal; Cyclic GMP; Cyclic GMP-Dependent Protein Kinase Type I; Cyclic GMP-Dependent Protein Kinases; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Formaldehyde; Guanylate Cyclase; Hyperalgesia; Male; Myelitis; N-Methylaspartate; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nociceptors; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Spinal Cord; Thionucleotides

Pain management in temporomandibular disorders (TMDs) often involves pharmacotherapy; however, the site of action for drugs that reduce TMD pain is not known. To determine possible central neural targets of analgesic drugs relevant in TMD pain, morphine or the N-methyl-D-aspartate receptor antagonist, MK-801, was given alone or in combination prior to TMJ injury. The number of neurons expressing the immediate early gene, c-fos, was quantified in the lower brainstem and upper cervical spinal cord as an index of neural activation. It was hypothesized that those neuronal groups most necessary for the sensory-discriminative aspects of acute TMJ injury should display the greatest reduction in c-fos expression after drug treatment. Barbiturate-anesthetized male rats were given morphine or MK-801 15 min prior to injection of mustard oil into the TMJ region. Morphine given centrally (i.c.v.) or peripherally (i.v.) caused a marked dose-related reduction in Fos-like immunoreactivity (Fos-LI) in laminae I-II at the middle portions of subnucleus caudalis (mid-Vc) and at the subnucleus caudalis/upper cervical spinal cord (Vc/C2) transition. Higher doses of morphine also reduced Fos-LI in the dorsal paratrigeminal region (dPa5) and at the subnucleus interpolaris/subnucleus caudalis (Vi/Vc-vl) transition. MK-801 given i.v. reduced Fos-LI only in laminae I-II at the Vc/C2 transition. Combined subthreshold doses of morphine and MK-801 reduced c-fos expression in the dPa5, mid-Vc, and the Vc/C2 transition region, below that predicted from the effects of either drug alone. These results suggest that neurons in laminae I-II of the mid-Vc and Vc/C2 transition and, to a lesser extent, in the dPa5 region play a critical role in mediating the sensory and/or reflex aspects of pain after acute injury to the TMJ region.

Topics: Analgesics, Opioid; Animals; Dizocilpine Maleate; Drug Interactions; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Genes, fos; Immunohistochemistry; Male; Medulla Oblongata; Morphine; Mustard Plant; Narcotic Antagonists; Pain; Plant Extracts; Plant Oils; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Temporomandibular Joint; Trigeminal Nucleus, Spinal

In capsaicin-pretreated mice, the nociceptive responses induced by intrathecally (i.t.) administered substance P (SP) were enhanced by N-methyl-D-aspartate (NMDA)-type receptor antagonists, dizocilpine (MK801) and D-2-amino-5-phosphonopentanoate (D-AP5) in a dose-dependent manner. Similar enhancement of SP-induced nociception was also observed in mice lacking the NMDA-type glutamate receptor NR2A/epsilon(1) subunit gene (GluRepsilon(1)(-/-) mice). On the other hand, GluRepsilon(1)(-/-) mice showed a marked enhancement of the peripheral nociceptive responses induced by intraplantar (i.pl.) injection of SP and bradykinin (BK). As the nociceptive responses to SP and BK (i.pl.) were both antagonized by CP-99994, an neurokinin(1) (NK(1)) antagonist (i.t.), these results suggest that GluRepsilon(1) receptor may play an inhibitory role in the downstream mechanisms of primary nociceptive SP neurones, possibly through activation of unidentified inhibitory neurones.

Topics: 2-Amino-5-phosphonovalerate; Analgesics; Animals; Bradykinin; Capsaicin; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Mice; Mice, Knockout; Nerve Fibers; Neurokinin-1 Receptor Antagonists; Pain; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Substance P

N-methyl-D-aspartate (NMDA) involvement in altered spinal neuron activity following peripheral nerve injury has been investigated in rats with chronic constriction of the sciatic nerve. Extracellular single neuron recordings were performed, in anesthetized, paralyzed rats, from the sciatic spinal cord segments (lumbar, L5-L6) ipsilateral to the constriction, and the effect of iontophoresized MK-801, an NMDA receptor non-competitive antagonist, was tested on baseline hyperactivity and hyperresponsiveness to noxious stimulation. The results show that baseline activity was unaffected whereas the noxious evoked responses were significantly modified, there being amplitude reduction and after-discharges suppression. The different role of NMDA in the abnormal pain states related to the abnormal neuronal activities is discussed.

Topics: Animals; Dizocilpine Maleate; Hot Temperature; Hyperalgesia; Male; Pain; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Reflex; Sciatic Nerve; Sciatic Neuropathy

Neuropathic pain is often associated with the appearance of pain in regions not related to the injured nerve. One mechanism that may underlie neuropathic pain is abnormal, spontaneous afferent drive which may contribute to NMDA-mediated central sensitization by the actions of glutamate and by the non-opioid actions of spinal dynorphin. In the present study, injuries to lumbar or sacral spinal nerves elicited elevation in spinal dynorphin content which correlated temporally and spatially with signs of neuropathic pain. The increase in spinal dynorphin content was coincident with the onset of tactile allodynia and thermal hyperalgesia. Injury to the lumbar (L(5)/L(6)) spinal nerves produced elevated spinal dynorphin content in the ipsilateral dorsal spinal quadrant at the L(5) and L(6) spinal segments and in the segments immediately adjacent. Lumbar nerve injury elicited ipsilateral tactile allodynia and thermal hyperalgesia of the hindpaw. In contrast, S(2) spinal nerve ligation elicited elevated dynorphin content in sacral spinal segments and bilaterally in the caudal lumbar spinal cord. The behavioral consequences of S(2) spinal nerve ligation were also bilateral, with tactile allodynia and thermal hyperalgesia seen in both hindpaws. Application of lidocaine to the site of S(2) ligation blocked thermal hyperalgesia and tactile allodynia of the hindpaws suggesting that afferent drive was critical to maintenance of the pain state. Spinal injection of antiserum to dynorphin A((1-17)) and of MK-801 both blocked thermal hyperalgesia, but not tactile allodynia, of the hindpaw after S(2) ligation. These data suggest that the elevated spinal dynorphin content consequent to peripheral nerve injury may drive sensitization of the spinal cord, in part through dynorphin acting directly or indirectly on the NMDA receptor complex. Furthermore, extrasegmental increases in spinal dynorphin content may partly underlie the development of extraterritorial neuropathic pain.

Topics: Anesthetics, Local; Animals; Antibodies, Blocking; Dizocilpine Maleate; Dynorphins; Excitatory Amino Acid Antagonists; Hot Temperature; Hyperalgesia; Immunoassay; Lidocaine; Ligation; Male; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Spinal Nerves

Pairings of a sweet taste and injection of morphine result in a learned avoidance of that taste and learned analgesic tolerance. This avoidance is mediated by the drug's peripheral effect, while learned tolerance involves activation of N-methyl-D-aspartate (NMDA) receptors. Exposure to a sweet taste also reduces morphine analgesia. We studied whether this taste-mediated reduction was reversed by an NMDA or peripheral opioid receptor antagonist.. To determine whether an intraoral infusion of saccharin would modulate morphine analgesia in rats, and to study the contribution of NMDA as well as peripheral opioid receptors to this modulation.. Six experiments used the rat's tail-flick response to study the effect of an intraoral infusion of a sodium saccharin solution on morphine analgesia, and the effects of the quaternary opioid receptor antagonist methylnaltrexone as well as the noncompetitive NMDA receptor antagonist MK-801 on this modulation of analgesia.. An intraoral infusion of saccharin reduced the analgesic effects of an intraperitoneal (i.p.) injection of morphine across a range of doses (experiment la), which was not attributable to an influence on tail-skin temperature (experiment 1b). This reduction was mediated by opioid receptors in the periphery and activation of NMDA receptors because morphine analgesia was reinstated by an i.p. injection of either methylnaltrexone (experiment 2a) or MK-801 (experiment 3a), which was not due to the effect of methylnaltrexone (experiment 2b) or MK-801 (experiment 3b) on morphine analgesia in the absence of saccharin.. These results document evidence for an antagonism of morphine analgesia by actions of the drug at peripheral opioid receptors and excitatory amino-acid activity at NMDA receptors. They are discussed with reference to the aversive motivational effects of peripheral opioid receptors and pain facilitatory circuits.

Topics: Analgesia; Analgesics, Opioid; Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Male; Morphine; Naltrexone; Narcotic Antagonists; Pain; Pain Measurement; Quaternary Ammonium Compounds; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Saccharin; Sweetening Agents

The effect of (+/-)-5-methyl-10,11-dihydro-5H-dibenzo(a,d) cyclohepten-5, 10-imine maleate (MK-801) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) injected intrathecally (i.t.) on the inhibition of the tail-flick response induced by morphine, D-Ala(2)-NmePhe(4)-Gly-ol-enkephalin (DAMGO), beta-endorphin, D-Pen(2,5)-enkephalin (DPDPE), or ¿(trans-3, 4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl] benzeocetamide)¿ (U50, 488H) administered i.t. was studied in ICR mice. The i.t. injection of MK-801 (2 microg) or CNQX (1 microg) alone did not affect the basal tail-flick response. Morphine (0.2 microg), DAMGO (0.8 ng), beta-endorphin (0.1 microg), DPDPE (0.5 microg) or U50, 488H (6 microg) caused only slight inhibition of the tail-flick response. CNQX injected i.t., but not MK-801, enhanced the inhibition of the tail-flick response induced by i.t. administered morphine, DAMGO, DPDPE or U50, 488H. However, CNQX or MK-801 injected i.t. was not effective in enhancing the inhibition of the tail-flick response induced by beta-endorphin administered i.t. The potentiating effect of CNQX on tail-flick inhibition induced by morphine, DAMGO, DPDPE or U50, 488H was blocked by naloxone (from 1 to 20 microg), yohimbine (from 1 to 20 microg) or methysergide (from 1 to 20 microg) injected i.t. in a dose-dependent manner. Our results suggest that the blockade of AMPA/kainate receptors located in the spinal cord appears to be involved in enhancing the inhibition of the tail-flick response induced by stimulation of spinal mu-, delta-, and kappa-opioid receptors. Furthermore, this potentiating action may be mediated by spinal noradrenergic and serotonergic receptors. However, N-methyl-D-aspartate receptors may not be involved in modulating the inhibition of the tail-flick response induced by various opioids administered spinally.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; 6-Cyano-7-nitroquinoxaline-2,3-dione; Analgesics, Opioid; Animals; beta-Endorphin; Dizocilpine Maleate; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Mice; Mice, Inbred ICR; Pain; Spinal Cord; Time Factors

The present study was designed to investigate the role of nitric oxide (NO), N-methyl-D-aspartate (NMDA) receptor and prostaglandins on hyperalgesia induced in rats by excitatory amino acids and the possibility that prostaglandins may act as the retrograde messenger in the spinal cord like NO. Nomega-nitro-L-arginine methyl ester (L-NAME; 500 microg/paw, intraplantarly (i.pl.)), MK-801 (10 microg/paw, i.pl.) or indomethacin (300 microg/paw, i.pl.) reduced the duration of phase 2 of the biting/licking and scratching (B/L + S) response induced by formalin injection from 255.6+/-16.7 s to 155.6+/-16.9, 172.25+/-33.3 or 205.6+/-16.7 s, respectively. L-NAME (0.3 mg, i.th.), MK-801 (8 microg, i.th.) or indomethacin (20 microg, i.th) reduced the duration of phase 2 of the B/L + S response induced by saline injection from 288.5+/-7.7s to 207.7+/-19.2, 184.6+/-7.7 or 1923+/-38.5 s, respectively. L-NAME or indomethacin injected into the spinal cord of the rat significantly reduced the hyperalgesia induced by NMDA (1 microg, i.th.) from 43.8+/-4.6% to 12.3+/-3.1 and 19.2+/-2.3%, respectively. It is assumed that NO produced by excitatory amino acids may increase prostaglandin production by cyclooxygenase activation. L-NAME, MK-801 or indomethacin injected into the rat spinal cord significantly reduced the hyperalgesia induced by prostaglandin E2 (PGE2, 25 ng, i.th.) in the tail-flick test from 40.6+/-3.5% to 18.2+/-3.2, 18.8+/-1.8 or 17.6+/-4.1%, respectively, but had little effect on hyperalgesia in the paw pressure test (except for indomethacin). In conclusion, NO and PGE2 affect the hyperalgesia induced by excitatory amino acids. It is suggested that PGE2, like NO, may act as a retrograde messenger in the spinal cord.

Topics: Animals; Dinoprostone; Dizocilpine Maleate; Excitatory Amino Acids; Formaldehyde; Hyperalgesia; Indomethacin; Male; N-Methylaspartate; NG-Nitroarginine Methyl Ester; Nitric Oxide; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Time Factors

We have previously demonstrated that the intrathecal administration of pertussis toxin produces a long-lasting thermal allodynia in mice. The purpose of the present studies was to compare the antinociceptive and the antiallodynic effects of drugs that are commonly used in treating neuropathic allodynia in untreated mice and in mice which had been administered vehicle or pertussis toxin intrathecally 7 days previously. In untreated mice, morphine, fentanyl, clonidine, oxymetazoline, desipramine and lidocaine, but not MK801, produced dose-related antinociception when tested using a 55 degrees C water tail-flick test. However, 7 days after the intrathecal injection of pertussis toxin, which induced a condition of thermal allodynia when tested using a 45 degrees C water bath, the full opioid and the full alpha(2)-adrenergic receptor agonists fentanyl and clonidine, but not the partial opioid nor the partial alpha(2)-adrenergic receptor agonists morphine and oxymetazoline, reversed the pertussis toxin-induced thermal allodynia. Moreover, lidocaine, desipramine, carbamazepine and MK801 failed to reverse the pertussis toxin-induced thermal allodynia. The present results suggest that decrements in G(i)/G(o)-protein function may be involved in initiating and/or maintaining some neuropathic pain states. Moreover, the results of the present study suggest that the use of full, but not partial, opioid or alpha(2)-agonists may be useful in the treatment of thermal allodynic pain states which may be due at least in part to inhibitory second messenger system dysfunction. Further, the underlying biochemistry of the apparent allodynic pain state induced by intrathecal administration of pertussis toxin warrants further investigation.

Topics: Animals; Carbamazepine; Clonidine; Desipramine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Fentanyl; Lidocaine; Male; Mice; Morphine; Oxymetazoline; Pain; Pain Measurement; Pertussis Toxin; Temperature; Virulence Factors, Bordetella

Effects of agonists and antagonists of P2X-purinoceptors on the regulation of the development of allodynia were examined in mice; the drugs were administered intrathecally to the spinal cord. Suramin (5, 10 microg) and pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS), antagonists of P2X receptors, inhibited prostaglandin (PG) E(2)-induced allodynia. PPADS did not block glutamate-induced allodynia. alpha,beta-Methylene ATP (alpha, beta-meATP), an agonist of P2X receptor, elicited allodynia. alpha, beta-me ATP-induced allodynia was blocked by co-administration of alpha,beta-meATP with PPADS, MK 801 or N(omega)-nitro-L-arginine methyl ester (L-NAME). Suramin at higher doses (20, 40 microg) induced allodynia, which was inhibited by MK 801 or L-NAME. These results suggest that ATP P2X receptors in the spinal cord are involved in the regulation of tactile allodynia. Glutamate receptor and nitric oxide systems play an important role in the development of allodynia produced by alpha,beta-meATP and suramin.

Topics: Adenosine Triphosphate; Animals; Dinoprostone; Dizocilpine Maleate; Injections, Spinal; Male; Mice; Mice, Inbred ICR; Neuroprotective Agents; Oxytocics; Pain; Platelet Aggregation Inhibitors; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Suramin

We found that spinorphin, a novel neuropeptide showed analgesia in a different manner compared with morphine. By measuring flexor responses induced by the intraplanter injection of substances, the presence of three different types of sensory neurons were demonstrated. Although spinorphin completely blocked 2-metylthioadenosine (2-MeS ATP, a P2X(3) agonist)-induced responses, morphine did not. On the other hand, morphine-induced blockade of bradykinin (BK, a B(2)-receptor agonist)-responses was attenuated by pertussis toxin (PTX) treatment, whereas that of spinorphin was not. Thus it is suggested that spinorphin has a spectrum of analgesia which covers the blockade of nociception insensitive to morphine.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adenosine; Analgesics, Opioid; Animals; Animals, Newborn; Bradykinin; Capsaicin; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Male; Mice; Morphine; Neurons, Afferent; Neuroprotective Agents; Oligopeptides; Pain; Pertussis Toxin; Piperidines; Protease Inhibitors; Purinergic Agonists; Thionucleosides; Time Factors; Virulence Factors, Bordetella

A diverse range of opioids and enantiomers were examined for their ability to displace binding at the [(3)H] MK-801-labelled site of the N-methyl-D-aspartate (NMDA) receptor in rat forebrain, displacement which is equitable with non-competitive NMDA receptor antagonist activity. Surprisingly, d-morphine, but not natural l-morphine, has low micromolar affinity for the site, suggesting clinical potential for racemic dl-morphine in the treatment of neuropathic pain with reduced development of tolerance. The opioid mu-receptor agonists: levorphanol, d- and dl-methadone, displayed similar properties. With the exception of the case of d-morphine, the structural requirements for affinity correspond closely with those previously found for the inhibitory effects of opioids on monoamine uptake.

Topics: Analgesics, Opioid; Animals; Dizocilpine Maleate; Morphine; Norepinephrine; Pain; Prosencephalon; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Serotonin; Stereoisomerism

The present study was designed to investigate the effect of a selective GABA(B) receptor agonist baclofen on the pain-like nociceptive behavior (scratching, biting and licking) induced by intrathecal (i.t.) injection of N-methyl-D-aspartate (NMDA) or (+)TAN-67, the enantiomorphs of 2-methyl-4aalpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aalpha-octahydro-quinolino[2,3,3g]isoquinoline (TAN-67), in the mouse. NMDA (0.05-0.2 microg/mouse) given i.t. immediately caused nociception in a dose-dependent manner. The nociception was significantly antagonized by i.t. co-injection with dizocilipine (0.1-1.0 microg/mouse), a non-competitive NMDA receptor antagonist. I.t. co-injection with baclofen (37.5-150 ng/mouse) significantly reduced the NMDA-induced nociceptive behavior in a dose-dependent fashion. The inhibition produced by baclofen was completely reversed by a selective GABA(B) receptor antagonist 2-hydroxysaclofen (0.15 and 0.3 microg/mouse). An i.t. injection of (+)TAN-67 at doses of 3.75-15 microg/mouse elicited a long-lasting and a dose-related nociception. The nociceptive behavior induced by (+)TAN-67 given i.t. was markedly suppressed by i.t. co-injection with baclofen (3-30 ng/mouse), and the inhibitory effect of baclofen was prevented by i.t. injection of 2-hydroxysaclofen (1 and 3 microg/ mouse). In addition, the (+)TAN-67-induced nociception was also attenuated by i.t. co-injection with dizocilipine (0.1-1.0 microg/mouse). These results suggest that spinal GABA(B) receptors may be implicated in the expression of nociception elicited by i.t. injection of either NMDA or (+)TAN-67 in the mouse.

Topics: Analgesics; Animals; Baclofen; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Agonists; Injections, Spinal; Male; Mice; N-Methylaspartate; Pain; Quinolines; Receptors, GABA-B; Spinal Cord

Painful peripheral neuropathies involve both axonal damage and an inflammation of the nerve. The role of the latter by itself was investigated by producing an experimental neuritis in the rat. The sciatic nerves were exposed at mid-thigh level and wrapped loosely in hemostatic oxidized cellulose (Oxycel) that on one side was saturated with an inflammatory stimulus, carrageenan (CARRA) or complete Freund's adjuvant (CFA), and on the other side saturated with saline. In other rats, a myositis was created by implanting Oxycel saturated with CFA into a pocket made in the biceps femoris at a position adjacent to where the nerve was treated. Pain-evoked responses from the plantar hind paws were tested before treatment and daily thereafter. Statistically significant heat- and mechano-hyperalgesia, and mechano- and cold-allodynia were present on the side of the inflamed nerve (CARRA or CFA) for 1-5 days after which responses returned to normal. There were no abnormal pain responses on the side of the saline-treated nerve, and none in the rats with the experimental myositis. The abnormal pain responses were inhibited by N-methyl-D-aspartate receptor blockade with MK-801, but were relatively resistant to the dose of morphine tested (10 mg/kg). Light microscopic examination of CARRA-treated nerves, harvested at the time of peak symptom severity, revealed that the treated region was mildly edematous and that there was an obvious endoneurial infiltration of immune cells (granulocytes and lymphocytes). There was either a complete absence of degeneration, or the degeneration of no more than a few tens of axons. Immunocytochemical staining for CD4 and CD8 T-lymphocyte markers revealed that both cell types were present in the epineurial and endoneurial compartments. The endoneurial T-cells appeared to derive from the endoneurial vasculature, rather than from migration across the nerve sheath. We conclude that a focal inflammation of the sciatic nerve produces neuropathic pain sensations in a distant region (the ipsilateral hind paw) and that this is not due to axonal damage. The neuropathic pain is specific to inflammation of the nerve because it was absent in animals with the experimental myositis and in those receiving sham-treatment. These results suggest that an acute episode of neuritis-evoked neuropathic pain may contribute to the genesis of chronically painful peripheral neuropathies, and that a chronic (or chronically recurrent) focal neuritis might produce neurop

Topics: Analysis of Variance; Animals; Carrageenan; Cold Temperature; Dizocilpine Maleate; Freund's Adjuvant; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Morphine; Neuritis, Autoimmune, Experimental; Pain; Physical Stimulation; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Sciatic Nerve

The effects of pretreatment with an NMDA receptor antagonist, MK-801, on c-Fos (Fos) expression in the lumbosacral spinal cord following repetitive, noxious (80 mmHg) or non-noxious (20 mmHg) colorectal distention (CRD) was examined immunocytochemically in awake and urethane anesthetized rats. In awake rats, noxious CRD induced Fos expression in the lumbosacral spinal cord. Pretreatment with MK-801 (0.1-1.0 mg/kg, i.p.) produced no change or an increase in noxious CRD induced-Fos expression and caused aversive side effects. In order to examine greater doses of MK-801, further experiments were performed in rats anesthetized with urethane. Both noxious and non-noxious CRD induced Fos in the lumbosacral spinal cord. Pretreatment with MK-801 (0.5, 1.0, 5.0 mg/kg, i.p.) dose-dependently attenuated noxious CRD-induced Fos by 20-40%. Five mg/kg MK-801 attenuated non-noxious CRD-induced Fos by 20%. Lesser doses did not significantly attenuate Fos expression. The laminar distribution of Fos following MK-801 pretreatment revealed a tendency towards the deeper laminae showing the greatest attenuation at the highest dose of MK-801. Protein plasma extravasation in the colon measured with Evan's blue dye showed no difference between rats without balloons, rats with balloons that were not distended and non-noxious CRD. There was significantly more extravasation following noxious CRD. Pretreatment with systemic MK-801 had no effect on plasma extravasation produced by noxious CRD. These data suggest that the induction of Fos in the lumbosacral spinal cord by noxious and non-noxious CRD is partially NMDA receptor mediated. However, NMDA receptor activation contributes significantly more to noxious than non-noxious CRD-induced Fos. Inflammation of the colon following noxious CRD likely contributes to sensitization of colonic afferents which may contribute to the increased NMDA receptor-mediated Fos following the noxious stimulus.

Topics: Animals; Colon; Dizocilpine Maleate; Gene Expression Regulation; Genes, fos; Inflammation; Male; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Rectum; Spinal Cord

This study examined the effects of exposing mice to forced walking stress on formalin-induced paw licking. At each observation period (0.5-6 h) after exposure to forced walking stress, a significant antinociceptive effect (stress-induced analgesia, SIA) was observed only in the second phase (from 10 to 30 min), but not in the first phase (from 0 to 10 min) of formalin-induced paw licking in mice. The present data showed that SIA induced by exposure to forced walking stress was dependent on duration of the stress (0.5-4 h). SIA was dose-dependently antagonized by the NMDA receptor antagonist dizocilipine (0.01-0.04 mg/kg) but not by naloxone (10 mg/kg). Thus, the present results suggest that exposure to forced walking stress could cause SIA which may be involved in the nonopioid system via NMDA receptors.

Topics: Analgesia; Animals; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Formaldehyde; Male; Mice; Naloxone; Narcotic Antagonists; Neuroprotective Agents; Pain; Pain Measurement; Physical Exertion; Receptors, N-Methyl-D-Aspartate; Stress, Physiological; Walking

The effects of different doses and time of administration of the N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801) on the development of the autotomy (self-mutilation) were studied in the rats receiving dorsal root ganglionectomy (DRGn). The rats without any treatment and those treated with normal saline immediately after DRGn were the control groups. Three groups of rats were treated with 0.1, 0.5 or 1.0 mg/kg of MK-801 immediately after DRGn, and another three were treated with 1.0 mg/kg of MK-801 2, 4, or 7 days after DRGn. The behavioral observations of these rats were quantified using an autotomy grading scale ranging from 0 to 19, and the scores were compared among these groups. The rats in the control groups manifested autotomy from 5 to 17 days after DRGn and all of them (100%) attained the highest autotomy score. Lower doses (0.1 or 0.5 mg/kg) of MK-801 had no effect on the development of the autotomy. In contrast, higher dose (1.0 mg/kg) of MK-801 administered immediately after DRGn significantly suppressed the autotomy as compared to the control groups (P < 0.01) and only 17% of the rats in this group attained the highest score. The antagonistic effect was retained when the treatment of MK-801 was delayed to 2 days after DRGn, however, it disappeared when the treatment was delayed to 4 or 7 days after DRGn. Thus, the antagonistic effect of MK-801 on the autotomy induced by DRGn was dose-related and time-dependent. The main role of the NMDA receptor in the development of the autotomy was within several days after DRGn.

Topics: Afferent Pathways; Animals; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Ganglia, Spinal; Injections, Intraperitoneal; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Self Mutilation; Time Factors

Mechanisms underlying the development of acute tolerance to the analgesic effect of opiates were investigated. In the rat tail-flick test, administration of naloxone (1 mg/kg, s.c.) 40 min after heroin (1 mg/kg, s.c.) was shown to induce hyperalgesia, indicative of a short-onset, opiate-activated pain facilitatory systems masking the opiate analgesia. Pretreatment with the N-methyl-D-aspartate receptor antagonist dizocilpine maleate blocked, in a dose-dependent manner, the naloxone-induced hyperalgesia and potentiated the heroin-induced analgesia. Using a schedule of two successive injections of 1 mg/kg heroin, acute tolerance was indicated by a marked reduction (-52%) in analgesia induced by the second dose. After pretreatment with dizocilpine maleate, the acute tolerance was abolished and the analgesic effects of both injections of heroin were strongly potentiated. These observations indicate that acute tolerance appears after the first exposure to opiates and stems from opiate activation of N-methyl-D-aspartate-dependent pain facilitatory systems.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Dizocilpine Maleate; Drug Tolerance; Heroin; Hyperalgesia; Male; Naloxone; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time

It is known that Substance P (SP) enhances glutamate- and N-methyl-D-aspartate (NMDA)-induced activity in spinal cord dorsal horn neurons and that this enhancement is important in the generation of wind-up and central sensitization. It is now known that SP and glutamate receptors are present on sensory axons in rat glabrous skin. This raises the issue as to whether SP and glutamate interact in the periphery. Using the tail skin in rats, the present study demonstrates 1) that unmyelinated axons at the dermal-epidermal junction immunostain for antibodies directed against NMDA, non-NMDA or SP (NK1) receptors; 2) that glutamate injected into the tail skin results in dose-dependent nociceptive behaviors interpreted as mechanical hyperalgesia, mechanical allodynia and thermal hyperalgesia, which are blocked following co-injection with glutamate antagonists; 3) that peripheral injection of SP potentiates glutamate-induced nociceptive behaviors in that the co-injection of SP+glutamate results in a significantly longer duration of behavioral responses compared to the responses seen following injection of either substance alone. These data provide support for the hypothesis that primary afferent neurons might well be subject to similar mechanisms that result in wind-up or central sensitization of spinal cord neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Axons; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Glutamic Acid; Hot Temperature; Hyperalgesia; Male; Microscopy, Immunoelectron; Neurons, Afferent; Nociceptors; Pain; Physical Stimulation; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Receptors, Neurokinin-1; Skin; Substance P; Tail

Intrathecal injection of a nitric oxide releasing compound, NOC-18, was used to define the role of nitric oxide (NO) in the spinal mechanism of neuropathic pain caused by unilateral chronic constriction injury to rat sciatic nerves. Paw withdrawal latency was used to evaluate nociception induced by thermal stimuli before surgery and afterwards at 1, 3, and 6 h, and on days 1, 2, 3, 4, 5, 8, and 12 after the nerve ligature. In the sham-surgery control groups, intrathecal injection of 10 or 100 microg of NOC-18 did not produce any change in withdrawal latencies. In rats with unilateral nerve ligation, however, administration of 1 or 10 microg, but not 0.1 microg, of NOC-18 significantly shortened the time in which thermal hyperalgesia developed after nerve injury. Injection of 1 microg of NOC-18 decreased the onset time of thermal hyperalgesia from 2 days to 3 h and with 10 microg hyperalgesia developed within 1 h after the nerve injury. The effects of intrathecal injection of MK-801, a N-methyl-D-aspartate (NMDA) receptor antagonist, N-nitro-L-arginine methyl ester (L-NAME), a NO synthase inhibitor, methylene blue (MB), a soluble guanylate cyclase inhibitor, and hemoglobin (Hb), a NO scavenger, on the development of thermal hyperalgesia after the sciatic nerve ligature were examined in the presence and absence of 1 and 10 microg of NOC-18. Acceleration of the development of thermal hyperalgesia induced by 1 and 10 microg NOC-18 was completely inhibited by Hb, but was not affected by either MK-801, L-NAME or MB. These findings indicate that NO plays an important role in the rapid development of thermal hyperalgesia after the nerve injury, but that facilitation of nociceptive processing in the spinal cord may entail an alternate to the NO-cyclic guanosine 3',5'-monophosphate (cGMP) pathway.

Topics: Animals; Antidotes; Cyclic GMP; Disease Models, Animal; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hemoglobins; Hot Temperature; Hyperalgesia; Ligation; Male; Methylene Blue; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitroso Compounds; Pain; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Spinal Cord

Acute dependence, defined as a precipitation of somatic signs by an antagonist, may occur after a single administration of an opiate drug. Because hyperalgesia is a consistent sign of the withdrawal syndrome, we tested the effectiveness of heroin, an opiate used by addicts, to induce pain facilitation even after a first exposure to the drug. In opiate-naive rats, subcutaneous injection of heroin induced analgesia followed by allodynia, a decrease in pain threshold. This latter phenomenon was observed in the absence of noxious stimuli and lasted several days. An N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 prevented such long-lasting allodynia. These results suggest that allodynia is an early sign reflecting neural plasticity associated with the development of dependence.

Topics: Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Heroin; Male; Narcotics; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Vocalization, Animal

We recently demonstrated that application of mustard oil (MO), a small-fiber excitant and inflammatory irritant, to the rat maxillary molar tooth pulp induces significant and prolonged increases in jaw muscle electromyographic (EMG) activity that are suggestive of central neuroplasticity. Because small-fiber afferents, including pulp afferents, access nociceptive neurons in trigeminal (V) subnucleus caudalis, this study examined whether pulpal application of MO induces neuroplastic changes in caudalis nociceptive neurons (wide dynamic range and nociceptive specific) and whether central N-methyl--aspartate (NMDA) receptor mechanisms are involved in these MO-induced neuroplastic changes. After pretreatment with vehicle (saline, 10 microliter i.t.) to the surface of the medulla, the pulpal application of MO to the maxillary molar tooth pulp produced a significant increase in neuronal spontaneous activity, a significant expansion of the pinch and/or tactile mechanoreceptive field (RF), a significant decrease in mechanical threshold, and significant increases in neuronal responses to graded pinch stimuli. Compared with vehicle-treated rats, pretreatment with the NMDA receptor antagonist MK-801 (10 microgram/10 microliter i.t.) followed by MO application to the pulp in another group of rats significantly reduced or abolished these MO-induced neuroplastic changes in nociceptive neurons. In another group of rats pretreated with saline (intrathecally), mineral oil application to the pulp did not show any significant changes in spontaneous activity or RF properties over the 40-min observation period. The pulpal application of MO in other rats (pretreated with saline, intrathecally) did not produce any significant neuroplastic changes in caudalis low-threshold mechanoreceptive neurons. These results indicate that the MO-induced activation of molar pulpal afferents can produce profound NMDA receptor-related neuroplastic changes in caudalis nociceptive neurons. Such neuroplastic changes may contribute to the hyperalgesia and spread of pain that can be associated with pulpal inflammation.

Topics: Animals; Dental Pulp; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Microelectrodes; Mineral Oil; Mustard Plant; Neuronal Plasticity; Pain; Physical Stimulation; Plant Extracts; Plant Oils; Plants, Medicinal; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Trigeminal Caudal Nucleus

Spinal cord injury can lead to an exaggeration of transmission through spinal pathways, resulting in muscle spasticity, chronic pain, and abnormal control of blood pressure and bladder function. These conditions are mediated, in part, by N-methyl-D-aspartate (NMDA) receptors on spinal neurons, but the effects of cord injury on the expression or function of these receptors is unknown. Therefore, antibodies to the NMDA-R1 receptor subunit and binding of [3H]MK-801 were used to assess NMDA receptors in the spinal cord. Receptor density in rats with intact spinal cords was compared to that in rats 1 and 2 weeks after spinal cord transection (SCT) at the mid-thoracic level. At 1 and 2 weeks after SCT, [3H]MK-801 binding was reduced in most laminae in cord segments caudal to the injury, whereas no decrease in amount of R1 subunit immunoreactivity was observed. No significant changes in [3H]MK-801 binding and NMDA-R1 immunoreactivity could be seen rostral to the transection. Since [3H]MK-801 binding requires an open ion channel, the discrepancy between [3H]MK-801 binding and immunocytochemistry may indicate a loss of functional receptors without a consistent change in their total number. Therefore, the exaggerated reflexes that are well established in rats 2 weeks after cord injury must be mediated by a mechanism that withstands attenuation of NMDA receptor function.

Topics: Animals; Autonomic Nervous System Diseases; Autoradiography; Chronic Disease; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Immunohistochemistry; Male; Muscle Spasticity; Nociceptors; Pain; Radioligand Assay; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Reflex, Abnormal; Spinal Cord; Spinal Cord Injuries; Tritium

Neuropathic pain remains a significant clinical problem. Current understanding implicates the spinal cord dorsal horn N-methyl-d-aspartate (NMDA) receptor apparatus in its pathogenesis. Previous reports have described NMDA antagonist reduction of nerve injury-induced thermal hyperalgesia and formalin injection-related electrical activity. We examined a panel of spinally administered NMDA antagonists in two models: allodynia evoked by tight ligation of the fifth and sixth lumbar spinal nerves (a model of chronic nerve injury pain), and the formalin paw test (a model wherein pretreatment with drug may preempt the development of a pain state). A wide range of efficacies was observed. In the nerve injury model, order of efficacy (expressed as percent of maximum possible effect +/- S.E.), at the maximum dose not yielding motor impairment, was memantine (96 +/- 5%) = AP5 (91 +/- 7%) > dextrorphan (64 +/- 11%) = dextromethorphan (65 +/- 22%) > MK801 (34 +/- 8%) > ketamine (18 +/- 6%). For the formalin test, the order of efficacy was AP5 (86 +/- 9%) > memantine (74 +/- 5%) > or = MK801 (67 +/- 16%) > dextrorphan (47 +/- 16%) > dextromethorphan (31 +/- 12%) > ketamine (17 +/- 15%). In the nerve injury model, no supraspinal action was seen after intracerebroventricular injections of dextromethorphan and ketamine. NMDA antagonists by the spinal route appear to be useful therapeutic agents for chemically induced facilitated pain as well as nerve injury induced tactile allodynia. It is not known what accounts for the wide range of efficacies.

Topics: 2-Amino-5-phosphonovalerate; Analgesics; Animals; Dextromethorphan; Dextrorphan; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Formaldehyde; Hyperalgesia; Injections, Spinal; Ketamine; Male; Memantine; Morphine; Pain; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Spinal Nerves; Touch

The present study demonstrates that local cutaneous administration of either the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK-801 or the non-NMDA glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) significantly attenuates formalin-induced nociceptive behaviors. Specifically, pretreatment with either drug reduced the magnitude and time course of lifting and licking behavior in the late phase of formalin pain; however, flinching behavior was not affected. In contrast, post-treatment of formalin pain with either antagonist did not affect lifting and licking behavior, although flinching behavior was mildly attenuated. We hypothesize that these actions result from blocking of peripheral glutamate receptors located on unmyelinated axons at the dermal-epidermal junction. These data suggest that peripheral glutamate receptors on cutaneous axons can be manipulated to reduce certain aspects of pain of peripheral origin. This route of administration offers the advantage of avoiding the side effects of systemic administration.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Axons; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Formaldehyde; Pain; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Skin; Stereotyped Behavior; Time Factors

MK801 (MK), an N-methyl-D-aspartate (NMDA) receptor antagonist, attenuates tolerance to spinal opioids. Whether this applies to other G-protein-coupled receptor systems is unknown. This study examines the effects of continuous spinal MK on tolerance to the antinociceptive effect of continuous spinal infusion of the alpha-2 agonist ST91 (ST). Intrathecal (i.t.) infusion pumps were implanted in rats which delivered for 7 days: saline (1 microl/h); ST (40 nmol/microl/h); MK (10 nmol/microl/h) + ST (40 nmol/microl/h); or MK (10 nmol/microl/h). Antinociception was measured daily on the hot plate. On day 8, groups received i.t. boluses of ST to generate dose-response curves. A separate ST-infused group received MK (10 nmol i.t.) on day 7. Each group received ST (40 nmol i.t.) 7 days after discontinuation of infusion. Co-infusion of MK with ST resulted in attenuation of the right shift in dose response seen in ST-infused rats and a small preservation of effect on daily testing. However, MK-infused rats showed a significant left shift in ST dose response. Acutely administered, MK did not restore ST sensitivity. One week after cessation of infusion, ST and ST + MK groups showed shorter duration of effect after i.t. ST bolus than controls. In conclusion, chronic spinal MK partially attenuates loss of sensitivity to chronic spinal ST. This supports the hypothesis that opioid- and adrenoceptor-induced tolerances are similarly modulated by the NMDA receptor. However, the increased sensitivity induced by MK alone suggests that NMDA receptor antagonism may not prevent the development of tolerance itself but may alter the expression of tolerance by inducing sensitivity via other alterations in cellular function.

Topics: Adrenergic alpha-Agonists; Animals; Clonidine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Hypersensitivity; Injections, Spinal; Male; Pain; Rats; Rats, Sprague-Dawley; Reaction Time

Previous studies showed that heat-hyperalgesia and mechanical allodynia produced by chronic constrictive injury of the sciatic nerve were differentially sensitive to the NMDA receptor antagonist dextrorphan and to morphine and other opioid receptor agonists. These results support the hypothesis that different kinds of neuropathic pain symptoms are caused by different pathological mechanisms. In the present study we determined whether mechanical and thermal allodynia produced by unilateral transection of the 'superior' caudal trunk which innervates the tail in rats were differentially sensitive to the non-competitive NMDA receptor antagonist MK-801. Injection of MK-801 (0.3 mg/kg, i.p.) prior to nerve injury delayed the emergence of both types of allodynia; the antagonist-treated rats exhibited neither mechanical nor thermal allodynia at least for 4 days after the injury, whereas untreated control rats exhibited clear signs of allodynia from the first day after the injury. MK-801 injection on post-injury day 14, when the allodynia was near peak severity, suppressed temporarily both the mechanical and thermal allodynia. These results suggest that the mechanical and thermal allodynia from partial denervation of the tail are both dependent on NMDA receptors in their induction and maintenance. Thus, our results do not support the notion that different pathological mechanisms underlie different modalities of neuropathic pain from partial peripheral nerve injury.

Topics: Animals; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Male; Pain; Peripheral Nervous System; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, N-Methyl-D-Aspartate; Temperature

The endogenous opioid peptide dynorphin A has non-opioid effects that can damage the spinal cord when given in high doses. Dynorphin has been shown to increase the receptive field size of spinal cord neurons and facilitate C-fiber-evoked reflexes. Furthermore, endogenous dynorphin levels increase following damage to the spinal cord, injury to peripheral nerves, or inflammation. In this study, sensory processing was characterized following a single, intrathecal injection of dynorphin A (1-17) in mice. A single intrathecal injection of dynorphin A (1-17) (3 nmol, i.t.) induced mechanical allodynia (hind paw, von Frey filaments) lasting 70 days, tactile allodynia (paint brush applied to flank) lasting 14 days, and cold allodynia (acetone applied to the dorsal hind paw) lasting 7 days. Similarly, dynorphin A (2-17) (3 nmol, i.t.), a non-opioid peptide, induced cold and tactile allodynia analogous to that induced by dynorphin A (1-17), indicating the importance of non-opioid receptors. Pretreatment with the NMDA antagonists, MK-801 and LY235959, but not the opioid antagonist, naloxone, blocked the induction of allodynia. Post-treatment with MK-801 only transiently blocked the dynorphin-induced allodynia, suggesting the NMDA receptors may be involved in the maintenance of allodynia as well as its induction. We have induced a long-lasting state of allodynia and hyperalgesia by a single intrathecal injection of dynorphin A (1-17) in mice. The allodynia induced by dynorphin required NMDA receptors rather than opioid receptors. This result is consistent with results in rats and with signs of clinically observed neuropathic pain. This effect of exogenously administered dynorphin raises the possibility that increased levels of endogenous dynorphins associated with spinal cord injuries may participate in the genesis and maintenance of neuropathic pain.

Topics: Animals; Dizocilpine Maleate; Dynorphins; Excitatory Amino Acid Antagonists; Injections, Spinal; Isoquinolines; Male; Mice; Mice, Inbred ICR; Narcotic Antagonists; Pain; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid

NMDA receptor involvement in neuroplastic changes induced by neonatal capsaicin treatment in trigeminal nociceptive neurons. J. Neurophysiol. 78: 2799-2803, 1997. This study examines whether 1) the neonatal loss of C-fiber afferents results in neuroplastic changes in the mechanoreceptive field (RF) properties and spontaneous activity of nociceptive neurons in trigeminal subnucleus caudalis (medullary dorsal horn) of adult rats, and that 2) N-methyl--aspartic acid (NMDA) receptor mechanisms are involved in these neuroplastic changes. Compared with vehicle-treated (i.e., control, CON) rats, capsaicin-treated (CAP) rats showed a marked increase in neuronal spontaneous activity and RF size per se, but these neuroplastic changes could be significantly reduced by MK-801 (1 mg/kg, iv), a noncompetitive NMDA receptor antagonist; RF size and spontaneous activity remained unchanged in CON rats after MK-801 administration and in CAP rats after vehicle (saline, iv). Administration of 7-chlorokynurenic acid intrathecally (5 microgram/10 microliter), an antagonist of strychnine-insensitive glycine bindin sites on the NMDA receptor, also significantly reduced neuronal RF size and spontaneous activity in CAP rats, but not in CON rats. These data provide evidence that C-fiber afferents play a role in shaping the properties of nociceptive neurons and that the neuroplastic changes involve NMDA receptor mechanisms.

Topics: Animals; Animals, Newborn; Capsaicin; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Functional Laterality; Hindlimb; Injections, Spinal; Kynurenic Acid; Male; Medulla Oblongata; Neuronal Plasticity; Neurons; Nociceptors; Pain; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Trigeminal Nerve

Exposure of animals to aversive events produces stress-induced analgesia. A common method of producing stress in animals is the cold-water swim (CWS). The present series of experiments examines the effect of CWS on tonic pain, as measured by the formalin test, and explores possible mechanisms of action. Experiment 1 demonstrates that a 3.5-min swim in 2 degrees C water produces a delayed nociceptive response (DNR), characterized by a prolonged period of no formalin responding which then begins and continues during the time when control animals, which have not received the CWS, are finished responding. The delayed response begins at 50-60 min postformalin injection, peaks at 80 min, and is still present at 120 min. Experiment 2 indicates that paw temperature effects are not responsible for the DNR, although core body temperature effects are a possible mechanism. However, systematic delays in the formalin injection following the CWS (Experiment 3) drastically altered the DNR even though core body temperature remained unchanged, suggesting that a decrease of core body temperature is insufficient to account for the DNR. Experiment 4 demonstrates that the NMDA antagonist MK-801 administered prior to the CWS dramatically reduces the DNR. The present experiment is the first study that reports a delay as long as 60 min in pain responding. It is concluded that the delayed response to formalin injection is the result of complex interactions involving peripheral mechanisms and central neuronal plasticity in which activity initiated by a noxious input persists after the cessation of the input as a consequence of a stressful event such as the cold-water swim.

Topics: Animals; Cold Temperature; Dizocilpine Maleate; Formaldehyde; Male; Neuronal Plasticity; Nociceptors; Pain; Pain Measurement; Rats; Swimming

We examined the antinociceptive effect of smilaxin B administered intracerebroventricularly (i.c.v.) in ICR mice. The tail-flick test was used as an analgesic assay. Smilaxin B showed a strong antinociceptive effect in a dose-dependent manner. Sulfated cholecystokinin (CCK-8s, 0.5 ng), muscimol (50ng), or MK-801 [(+/-)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5, 10-imine maleate, 1 microgram] injected i.c.v. significantly reduced inhibition of the tail-flick response induced by smilaxin B administered i.c.v. However, naloxone (2 microgram), baclofen (10 ng), or CNQX (6-cyano-7- nitroquinoxaline-2,3-dione, 0.5 microgram) injected i.c.v. did not affect inhibition of the tail-flick response induced by similaxin B administered i.c.v. The intrathecal (i.t.) injection of yohimbine (20 micrograms), but not methysergide (20 micrograms) and naloxone (2 microgram), significantly attenuated inhibition of the tail-flick response. induced by smilaxin B administered i.c.v. Our results suggest that GABAA or NMDA receptors but not opioid, GABAB, and non-NMDA receptors located at the supraspinal level may play important roles in the production of antinociception induced by smilaxin B administered supraspinally. Furthermore, smilaxin B administered supraspinally. may produce its antinociception by activating descending noradrenergic- but not opioidergic- and serotonergic-neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Cerebral Ventricles; Dizocilpine Maleate; Glycosides; Injections, Intraventricular; Injections, Spinal; Male; Methysergide; Mice; Mice, Inbred ICR; Muscimol; Naloxone; Pain; Sincalide; Spinal Cord; Spirostans; Yohimbine

Neuropathic pain states are accompanied by increased sensitivity to both noxious and non-noxious sensory stimuli, characterized as hyperalgesia and allodynia, respectively. In animal models of neuropathic pain, the presence of hyperalgesia and allodynia are accompanied by neuroplastic changes including increased spinal levels of substance P, cholecystokinin (CCK), and dynorphin. N-Methyl-D-aspartate (NMDA) receptors appear to be involved in maintaining the central sensitivity which contributes to neuropathic pain. In addition to its opioid activities, dynorphin has been suggested to act at the NMDA receptor complex. In an attempt to mimic the increased levels of spinal dynorphin seen in animal models of neuropathic pain, rats received a single intrathecal (i.t.) injection of dynorphin A(1-17), dynorphin A(1-13), dynorphin A(2-17) or dynorphin A(2-13) through indwelling catheters. Tactile allodynia was determined by measuring response threshold to probing with von Frey filaments. Dynorphin A(1-17) administration evoked significant and long-lasting tactile allodynia (i.e. > 60 days). Likewise, the i.t. administration of dynorphin A(1-13) or dynorphin A(2-17) or dynorphin A(2-13) also produced long-lasting tactile allodynia. Intrathecal pretreatment, but not post-treatment, with MK-801 prevented dynorphin A(1-17)-induced development of allodynia; i.t. administration of MK-801 alone had no effect on responses to tactile stimuli. In contrast, i.t. pretreatment with naloxone did not affect the development of tactile allodynia induced by dynorphin A(1-17) or alter sensory threshold when given alone. These results demonstrate that a single dose of dynorphin A, or its des-Tyr fragments, produces long-lasting allodynia which may be irreversible in the rat. Further, this effect appears to be mediated through activation of NMDA, rather than opioid, receptors. While the precise mechanisms underlying the development and maintenance of the allodynia is unclear, it seems possible that dynorphin may produce changes in the spinal cord, which may contribute to the development of signs reminiscent of a "neuropathic' state. Given that levels of dynorphin are elevated following nerve injury, it seems reasonable to speculate that dynorphin may have a pathologically relevant role in neuropathic pain states.

Topics: Animals; Chronic Disease; Dizocilpine Maleate; Dynorphins; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Naloxone; Narcotic Antagonists; Pain; Peptide Fragments; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley; Sensory Thresholds

We have examined and compared the effects of systemically applied MK-801, an NMDA receptor/channel blocker, on the wind-up and facilitation of the flexor reflex during and after conditioning stimulation (CS) of C-afferents in rats with intact sciatic nerves or 13-16 days after axotomy. In rats with intact sciatic nerves, intravenous MK-801 (0.5 mg/kg) partially reduced wind-up and totally blocked reflex facilitation following C-fiber CS to the sural nerve. In contrast, 13-16 days after unilateral section of the sciatic nerve, the same dose of MK-801 failed to reduce the wind-up and reflex facilitation following C-fiber CS to the axotomized sural nerve, although the duration of reflex facilitation was significantly shortened. These findings indicate that the involvement of NMDA receptors in mediating activity-dependent spinal hyperexcitability is substantially reduced after peripheral nerve section, possibly reflecting a reduced release of glutamate by primary sensory afferents.

Topics: Animals; Axons; Dizocilpine Maleate; Electric Stimulation; Female; Neuronal Plasticity; Pain; Peripheral Nerves; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Reflex, Stretch; Spinal Cord

Nerve ligation injury in rats may represent a useful model of some clinical neuropathic pains. Activation of N-methyl-D-aspartate (NMDA) receptors may maintain central sensitivity and contribute to neuropathic pain. Here, nerve injury was produced by unilateral ligation of the L5 and L6 spinal roots of the sciatic nerve of rats. Catheters were inserted for intrathecal (i.th.) or local delivery of drugs at the site of nerve ligation. Acute nociception was measured by the 55 degrees C water tail flick test in sham-operated and nerve-injured rats, and allodynia was determined by measuring response to von Frey filaments. In sham-operated rats, morphine (30 micrograms, i.th.) produced a 60 +/- 14.4% MPE (maximal possible effect). MK-801 pretreatment did not alter tail-flick latency or morphine antinociception in sham-operated rats. In nerve-injured rats, morphine (30 micrograms, i.th.) produced a significantly lower antinociceptive effect than in controls (34 +/- 6.3% MPE). While MK-801 alone did not alter tail-flick latency in nerve-injured rats, it significantly enhanced the antinociceptive effect of morphine to 84 +/- 16.0% MPE. Bupivacaine (0.2 ml, 0.75% w/v) at the site of injury also significantly increased the efficacy of morphine (100 +/- 0% MPE) without affecting tail flick latency alone. Bupivacaine administered at the site of injury also produced a significant antiallodynic effect of 94 +/- 7.4% MPE. The reduction in antinociceptive efficacy of i.th. morphine in nerve injured rats may be due, in part, to an ongoing spontaneous activity initiated by ectopic foci at the site of injury, and possible NMDA receptor-mediated activity of spinal neurons.

Topics: Analgesics, Opioid; Anesthetics, Local; Animals; Bupivacaine; Dizocilpine Maleate; Drug Tolerance; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Morphine; Nerve Block; Neurons, Afferent; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, N-Methyl-D-Aspartate; Sciatic Nerve; Spinal Cord

Substance P, a putative neurotransmitter or neuromodulator of nociception or pain in the spinal cord, exhibits both antinociceptive and hyperalgesic properties. Investigators have shown that the N-terminal metabolite of substance P, substance P(1-7), produces naloxone-reversible antinociception when given supraspinally and systemically in mice and hyperalgesia when injected intrathecally in rats. The goal of our investigation was to identify the receptors mediating these actions of substance P(1-7) at the initial site of release of substance P, i.e. in the spinal cord. Thirty minutes after intrathecal injection, substance P(1-7) produced naloxone-reversible antinociception in a dose-dependent manner in the abdominal stretch assay. When administered with naloxone, substance P(1-7) produced hyperalgesia 5 and 10 min after injection, which was inhibited by dizocilpine (MK-801), a phencyclidine ligand and non-competitive antagonist of N-methyl-D-aspartate. Antinociception was inhibited by the mu-selective opioid antagonist beta-funaltrexamine, but not by the mu 1-selective opioid antagonist naloxonazine or the delta-selective antagonist naltrindole, indicating a mu 2-opioid receptor-mediated effect. These findings suggest that the N-terminal portion of substance P may modulate nociception or pain, as demonstrated in the acetic acid abdominal stretch (writhing) assay, via activation of two different receptor systems. Substance P(1-7)-induced hyperalgesia is mediated by a phencyclidine-sensitive mechanism and antinociception involves activity at mu-opioid, most likely mu 2, receptors.

Topics: Animals; Biological Assay; Disease Models, Animal; Dizocilpine Maleate; Hyperalgesia; Injections, Spinal; Injections, Subcutaneous; Male; Mice; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Peptide Fragments; Phencyclidine; Receptors, Opioid, mu; Spinal Cord; Substance P

Repetitive exposure of rats to a hot plate induced a novel non-opioid form of stress induced analgesia. The exposure caused a persistent 1.5-2 s increase in tail flick latency which was not attenuated by systemic naltrexone, but was completely inhibited by systemic MK-801. Concomitantly, alterations occurred in the ability to pharmacologically distinguish multiple beta-endorphin receptors in the periaqueductal gray. Thus, in response to different forms of stress, different pathways may be activated by beta-endorphin, resulting in stress induced analgesias with varied pharmacological characteristics (e.g., opioid and non-opioid).

Topics: Amino Acid Sequence; Analgesia; Animals; beta-Endorphin; Cytidine Triphosphate; Dizocilpine Maleate; Heating; Male; Microinjections; Molecular Sequence Data; Morphine; Narcotic Antagonists; Pain; Periaqueductal Gray; Rats; Rats, Sprague-Dawley; Stress, Physiological; Synaptic Transmission

The glycine B receptor partial agonists L 687,414, D-cycloserine and (+)-HA 966, and the glycine B receptor antagonists MDL 29,951 and 5,7-dichloro-2,4 dihydroxy-3-phenyl-quinoline dione (DCPQ) dose-dependently inhibited the late phase (LP) of formalin-induced licking (FIL) elicited by intraplantar formalin in mice at doses exerting little motor disruption in the rotarod test. In distinction, the early phase (EP) of FIL and the writhing response to intra-abdominal acetic acid were little influenced and, irrespective of stimulus intensity, they failed to modify the tail-flick response to phasic, thermal or mechanical stimulation of the tail. In contrast to glycine B ligands, competitive antagonists at the NMDA receptor recognition site (CPP, CGS 19755, CGP 34879 and 39551) and blockers of the associated ion channel ((+)-MK 801, (-)-MK 801, memantine and ketamine) all blocked both the LP and EP of FIL and induced ataxia at comparable doses. In conclusion, normalization of transmission at NMDA receptors by inhibition of the coupled glycine B site preferentially elicits antinociception against prolonged (chemical) noxious stimulation in the absence of a marked influence upon motor coordination.

Topics: 2-Amino-5-phosphonovalerate; Acetates; Acetic Acid; Animals; Anticonvulsants; Cycloserine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Formaldehyde; Indoles; Ligands; Male; Mice; Mice, Inbred Strains; Motor Activity; Pain; Propionates; Pyrrolidinones; Quinolones; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate

In response to concerns over the clinical relevance of analgesic testing paradigms which involve acute nociceptive stimuli, the present research examined the utility of the conditioned place preference (CPP) paradigm as a novel approach for determination of analgesic drug efficacy against chronic nociception. Rats display preferences for environments that have been previously paired with positively reinforcing drugs; whether place preference to the negatively reinforcing effects of analgesic drugs in an animal model of chronic pain occurs is yet unknown. The present research sought to determine whether animals experiencing chronic pain would display a place preference for an environment paired with analgesic drug treatment. Persistent inflammatory nociception was induced by unilateral injections of complete Freund's adjuvant (0.1 ml) into the rat hind paw. Place preference to the opiate agonist morphine, the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the non-steroidal anti-inflammatory drug (NSAID) indomethacin was examined in 3 separate experiments. Rats received 8 counter-balanced conditioning trials (4 drug, 4 no-drug) of 60 min each with various drug doses (morphine: 3.0 and 10.0 mg/kg; indomethacin: 2.5 and 5.0 mg/kg; MK-801: 0.03, 0.1 and 0.3 mg/kg, i.p.) or vehicle serving as the reinforcing stimuli in a 3 compartment (2 stimuli, 1 neutral) place preference apparatus. In general, morphine place preference was observed in both inflamed and non-inflamed groups; inflamed groups exhibited enhanced morphine place preference than non-inflamed groups. MK-801 produced a low-dose place preference in inflamed animals; higher doses of MK-801 produced a place aversion in both inflamed and non-inflamed groups. Indomethacin failed to produced place preference in either inflamed or non-inflamed groups. These data demonstrate that the negatively reinforcing properties of analgesic drugs can be assessed via the CPP paradigm. In addition, this paradigm offers greater clinical relevance as animals determine drug efficacy without the involvement of high-intensity, phasic nociceptive stimulation.

Topics: Analgesics; Animals; Chronic Disease; Conditioning, Operant; Dizocilpine Maleate; Edema; Hot Temperature; Indomethacin; Male; Morphine; Nociceptors; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Reinforcement, Psychology

Topics: Animals; Bupivacaine; Disease Models, Animal; Dizocilpine Maleate; Humans; Neuronal Plasticity; Nitric Oxide; Nociceptors; Pain; Receptors, N-Methyl-D-Aspartate; Spinal Cord

In a rat model of morphine tolerance, we examined the hypotheses that thermal hyperalgesia to radiant heat develops in association with the development of morphine tolerance and that both the development and expression of thermal hyperalgesia in morphine-tolerant rats are mediated by central NMDA and non-NMDA receptors and subsequent protein kinase C (PKC) activation. Tolerance to the analgesic effect of morphine was developed in rats utilizing an intrathecal repeated treatment regimen. The development of morphine tolerance and thermal hyperalgesia was examined by employing the tail-flick test and paw-withdrawal test, respectively. Intrathecal MK 801 (an NMDA receptor antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; a non-NMDA receptor antagonist), or GM1 ganglioside (an intracellular PKC inhibitor) treatment was given to examine the effects of these agents on the development and expression of thermal hyperalgesia in morphine-tolerant rats. Tolerance to the analgesic effect of morphine was reliably developed in rats following once daily intrathecal (onto the lumbosacral spinal cord) injection of 10 micrograms of morphine sulfate for 8 consecutive days as demonstrated by the decreased analgesia following morphine administration on day 8 as compared to that on day 1. In association with the development of morphine tolerance, thermal hyperalgesia to radiant heat developed in these same rats. Paw-withdrawal latencies were reliably decreased in morphine-tolerant rats as compared to nontolerant (saline) controls when tested on day 8 before the last morphine treatment and on day 10 (i.e., 48 hr after the last morphine treatment). The coincident development of morphine tolerance and thermal hyperalgesia was potently prevented by intrathecal coadministration of morphine with MK 801 (10 nmol) or GM1 (160 nmol), and partially by CNQX (80 nmol). MK 801 (5, 10 nmol, not 2.5 nmol) and CNQX (80, 160 nmol, not 40 nmol), but not GM1 (160 nmol), also reliably reversed thermal hyperalgesia in rats rendered tolerant to morphine when tested 30 min after each drug treatment on day 10 (48 hr after the last morphine treatment). The data indicate that thermal hyperalgesia develops in association with the development of morphine tolerance and that the coactivation of central NMDA and non-NMDA receptors is crucial for both the development and expression of thermal hyperalgesia in morphine-tolerant rats. Furthermore, intracellular PKC activation plays a critical role in the

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dizocilpine Maleate; Drug Tolerance; Excitatory Amino Acid Antagonists; G(M1) Ganglioside; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Morphine; Pain; Protein Kinase C; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate

Excitatory amino acid receptors have been implicated in mediating pain. 3-((+-)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a competitive N-methyl-D-aspartate (NMDA) antagonist and MK-801, a phencyclidine (PCP) ligand and non-competitive NMDA antagonist, were injected intrathecally in mice alone or in combination with 6,7-dinitroquinoxaline-2,3-dione (DNQX), a non-NMDA antagonist. When tested in the formalin model of pain, antinociception following CPP plus DNQX was greater than that after MK-801 plus DNQX in both the acute and tonic phases. These dissimilarities are not consistent with activity of CPP and MK-801 at the same sites in the spinal cord.

Topics: Animals; Dizocilpine Maleate; Formaldehyde; Injections, Spinal; Male; Mice; Pain; Pain Measurement; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate

The effects of acute administration of dizocilpine (MK-801) at different perioperative times on autotomy behavior after sciatic and saphenous nerve transection were studied in the mouse. Control mice developed a severe self-mutilating behavior starting 1-3 days postoperation and reaching a maximum by 11 days. Mice injected with a single dose of dizocilpine (0.4 mg/kg i.p.) before operation, the 1st or 3rd postoperative day autotomized significantly less than controls. An 1-wk treatment with the same dose once a day did not show further benefit. A single administration of dizocilpine the 5th day after surgery slightly halted further progression of autotomy. Dizocilpine did not have any deleterious effect on normal peripheral nerve function. These results suggest that NMDA receptor blockade prevents development of hyperalgesia and neuropathic pain after peripheral nerve injuries but only when it is administered before or during the first 3 days after injury.

Topics: Animals; Axons; Denervation; Dizocilpine Maleate; Female; Hindlimb; Mice; Pain; Peripheral Nerve Injuries; Peripheral Nerves; Sciatic Nerve; Self Mutilation

An animal model of peripheral neuropathy resulting in a unilateral hyperalgesia has recently been developed. The N-methyl-D-aspartate (NMDA) antagonist MK-801 reduces the thermal hyperalgesia observed in this model. The goal of the present study was to determine whether the immunohistochemical changes in dorsal horn peptides shown by neuropathic animals could also be modified by MK-801. Changes in immunostaining densities of substance P (SP) and calcitonin gene-related peptide (CGRP) within the spinal cord of untreated (reference population) neuropathic rats and that of neuropathic rats treated for 7 days with MK-801 were quantified and compared. The reference neuropathic animals demonstrated thermal hyperalgesia and an ipsilateral decrease in SP staining density without an accompanying change in CGRP staining density. MK-801-treated animals showed a dose-dependent attenuation of the thermal hyperalgesia. The expected ipsilateral decrease in SP was prevented in neuropathic animals treated with a low dose (0.5 mg/kg) of MK-801, while a higher dose of MK-801 (1 mg/kg) resulted in an increase in SP staining ipsilateral to the injury. MK-801 treatment in naive rats caused a global increase in both SP and CGRP staining in the dorsal horn. However, this global increase failed to mask the changes in staining density in neuropathic animals following MK-801 treatment. The results suggest a functional interaction between excitatory amino acids (EAAs) and SP, with activation of NMDA receptors mediating depletion of SP in neuropathic animals. It is suggested that SP-containing interneurons are a target of the EAAs in the dorsal horn.

Topics: Animals; Calcitonin Gene-Related Peptide; Dizocilpine Maleate; Immunohistochemistry; Male; Pain; Perfusion; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley; Spinal Cord; Substance P

Topics: Analysis of Variance; Animals; Capsaicin; Dizocilpine Maleate; Haloperidol; Kainic Acid; Male; Mice; Pain; Peptide Fragments; Piperazines; Receptors, N-Methyl-D-Aspartate; Substance P

Single neuron activities responding to peripheral stimuli with short latencies were recorded within the thalamic nucleus ventralis posterolateralis (VPL) after transection of the spinothalamic tract (STT) in the cat under alpha-chloralose anesthesia. The VPL neurons showed spontaneous and evoked hyperactivity after STT transection, which was revealed at 1-2 weeks. The spontaneous hyperactivity further progressed until 3-4 weeks. These hyperactivities were observed in core-area neurons as well as neurons found in the shell area, suggesting that some, if not many, of the N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801, 4-16 mg; i.v.) attenuated both the spontaneous and evoked hyperactivity observed after STT transection. No such effects were demonstrated in sham-operated animals. These findings suggest that VPL neurons become hyperactive after STT transection through recruitment of NMDA receptors. The hyperactivity of VPL neurons may represent an important background process in the production of deafferentation pain induced by lesions involving the STT.

Topics: Amino Acids; Animals; Cats; Dizocilpine Maleate; Neural Pathways; Neurons; Neurons, Afferent; Neurotransmitter Agents; Pain; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Thalamic Nuclei

We have previously reported that the response latency in the mouse hot-plate test is affected differently by spinal intrathecal (i.t.) injection of competitive and non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, in that only the former produces an antinociceptive effect. Since the lipophilic non-competitive antagonists will redistribute rapidly from the spinal injection site, it is conceivable that they reach sites where they counteract the spinal antinociceptive effect. In the present study, we have tested this hypothesis by comparing the antinociceptive effect of the competitive NMDA receptor antagonist CGS 19755 and the non-competitive NMDA receptor antagonist MK-801 after i.t., intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration as well as after combinations thereof. CGS 19755 injected i.p. or i.c.v. and MK-801 injected i.p. or i.t. attenuated the antinociceptive effect of i.t. injected CGS 19755. Both i.p. and i.c.v. administration of either CGS 19755 or MK-801 dose-dependently impaired motor function without producing antinociceptive effects. Thus, the effect of CGS 19755 and MK-801 on the motor system was found to be separate from their antinociceptive effect. In a separate experiment, changes in hind-paw skin temperature were excluded as a possible confounding factor. These findings demonstrate that supraspinal systems can limit the spinal antinociceptive effect of NMDA receptor antagonists.

Topics: Animals; Cerebral Ventricles; Dizocilpine Maleate; Dose-Response Relationship, Drug; Hot Temperature; Injections, Intraperitoneal; Injections, Intraventricular; Injections, Spinal; Mice; Mice, Inbred Strains; N-Methylaspartate; Pain; Pipecolic Acids; Receptors, N-Methyl-D-Aspartate; Skin Temperature; Spinal Cord; Time Factors

We have previously reported that transient spinal cord ischemia induced a behavioral hypersensitivity (allodynia) to innocuous cutaneous mechanical stimulation in rats. The spinal ischemia-induced allodynia was not relieved by morphine, but it was relieved by the gamma-aminobutyric acid (GABA)-B receptor agonist baclofen, indicating that the allodynia may be related to dysfunction of the spinal GABA-ergic inhibitory system. In the present study we report that systemic application of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), an antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor for excitatory amino acids, dose-dependently relieved allodynia after spinal cord ischemia. The analgesic effect of NBQX at a low dose (7.5 mg/kg) was not accompanied by motor deficits or sedation. On the other hand, the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) only partially alleviated allodynia, even at doses that produced severe motor deficits. It is suggested that the abnormal, possibly painful, sensations elicited by innocuous mechanical stimulation observed after spinal cord ischemia may be mediated by excitatory amino acids, acting mainly on the AMPA receptor. Antagonists of excitatory amino acid receptors, especially at the AMPA site, may be effective in treating pain conditions where input from low threshold afferents triggers painful sensations.

Topics: Animals; Dizocilpine Maleate; Female; Pain; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Reperfusion Injury; Skin Physiological Phenomena; Spinal Cord; Vocalization, Animal

Topics: Animals; Denervation; Dizocilpine Maleate; Pain; Rats; Receptors, N-Methyl-D-Aspartate

Subcutaneous injection of formalin produces a biphasic pain response: an early, transient phase followed by a late tonic phase. The present study examined the involvement of the N-methyl-D-aspartic acid (NMDA) receptor in the development of the late pain produced following subcutaneous injection of formalin into the hind paw in mice. Blockade of the NMDA receptor by its non-competitive antagonist, MK-801, prior to formalin injection, but not after, reduced pain during the late phase. Similarly, blockade of the NMDA receptor allosteric site by the novel glycine site antagonist, ACEA-1011, also reduced the pain response in the late phase. These results suggest that the development of the late phase of formalin pain is due to NMDA-mediated activity during the early phase.

Topics: Analgesics; Animals; Behavior, Animal; Dizocilpine Maleate; Foot; Formaldehyde; Injections, Subcutaneous; Male; Mice; Mice, Inbred Strains; Pain; Quinoxalines; Receptors, N-Methyl-D-Aspartate

We studied the effects of intrathecally administered strychnine (STR; glycine antagonist; 10 or 30 micrograms) and bicuculline (BIC; GABAA antagonist 1 or 3 micrograms) on the thermal hyperalgesia which occurs following sciatic nerve constriction injury in rats. Following unilateral application of loose ligatures around the sciatic nerve, all rats typically displayed an ipsilateral thermal hyperalgesia on day 7. Intrathecal STR or BIC administered just after the nerve lesion and on days 1 and 2 after the nerve lesion significantly enhanced in a dose-dependent fashion the magnitude of the thermal hyperalgesia normally observed on day 7, as compared to intrathecal saline (for STR: 30 micrograms > 10 micrograms > or = saline; for BIC: 30 micrograms > 10 micrograms > or = saline, p < 0.05). Intrathecal MK-801, an N-methyl-D-aspartate antagonist, was without effect upon the response latency of the normal or sham operated paw, but selectively reversed the hyperalgesia. These results suggest that the loss of a spinal STR- and BIC-sensitive inhibition augments development of the hyperalgesia induced by chronic nerve compression.

Topics: Animals; Bicuculline; Dizocilpine Maleate; Dose-Response Relationship, Drug; gamma-Aminobutyric Acid; Glycine; Hot Temperature; Injections, Spinal; Male; N-Methylaspartate; Nerve Crush; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Strychnine

This study evaluated the effects of intrathecally coadministered morphine and the N-methyl-D-aspartate (NMDA) antagonist (+)5-methyl-10,11-dihydro-5H- dibenzocyclohepten-5,10-imine maleate (MK-801) on the thermally evoked hindpaw withdrawal latency (PWL) in rats with one paw (ipsilteral) rendered hyperesthetic by the unilateral application of loose ligatures to the sciatic nerve (delta PWL (+/- S.D.) = PWLhyperesthetic paw - PWLnormal paw = -3.1 +/- 1.2 s). Intrathecal morphine produced a dose-dependent (0.1-10 micrograms; P less than 0.0001) elevation in the thermal response latency of both the contralateral (normal) and ipsilateral (hyperesthetic) paw. delta PWL did not vary with morphine, indicating that the dose-response curves were parallel but shifted to the right for the hyperesthetic paw. For the normal paw, MK-801 (10 micrograms) was without effect upon the response latency; whereas, the response latency of the hyperesthetic paw was elevated to the same as the normal paw, i.e. the hyperesthesia was selectively abolished (delta PWL (+/- S.D.) = -0.067 +/- 2.73). Co-administration of MK-801 with morphine did not alter the effects of morphine in the normal paw, but reduced the delta PWL for each dose of morphine. These results suggest that NMDA antagonism (1) does not alter the thermal sensitivity in the normal paw, (2) selectively abolishes the hypersensitivity of the hypersthetic paw and (3) has a simple additive interaction with the antinociceptive effects of morphine in the hyperesthetic paw.

Topics: Animals; Disease Models, Animal; Dizocilpine Maleate; Drug Interactions; Hot Temperature; Hyperesthesia; Injections, Spinal; Male; Morphine; N-Methylaspartate; Pain; Peripheral Nervous System Diseases; Rats; Rats, Inbred Strains; Sciatic Nerve; Spinal Cord; Time Factors

The chiral forms of ketamine were applied as probes for N-methyl-D-aspartate receptor-mediated neurotransmission in humans. Both enantiomers, in clinically relevant concentrations, displaced [3H]dizocilpine (MK 801) from specific binding sites (phencyclidine sites) in membrane fractions of brain homogenates. (S)-Ketamine was at least 4 times as potent as (R)-ketamine in this respect. In healthy volunteers, the most obvious effect of subanesthetic doses of both enantiomers was altered sensory perception. (S)-Ketamine was 4 times as potent as (R)-ketamine in reducing pain perception and in causing auditory and visual disturbances. Both enantiomers caused proprioceptive disturbances (feelings of detachment from the body) and slightly reduced the ability to recall objects seen after administration of the drugs. The ability to recall objects seen immediately before drug exposure was unaffected. The results are in accordance with the hypothesis that inhibition of sensory perception by ketamine in subanesthetic concentrations is due to N-methyl-D-aspartate receptor blockade. It is suggested that N-methyl-D-aspartate receptor-mediated transmission is involved in the processing of sensory information in the human brain.

Topics: Adult; Dizocilpine Maleate; Hearing; Humans; Ketamine; Male; Memory; Pain; Perception; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Receptors, Phencyclidine; Sensation; Stereoisomerism; Vision, Ocular

Subcutaneous injection of formalin produces a biphasic pain response: a transient early phase followed by a tonic late phase. It has recently been suggested that development of the late phase depends upon the presence of the early one. In support of this suggestion, we now demonstrate that blocking the early phase by stress-induced analgesia prevents development of the late phase, whereas the same stressor given after the first phase does not. Both phases are manifested when stress-induced analgesia is blocked by the N-methyl-D-aspartate (NMDA) or opiate antagonists, MK-801 and naloxone.

Topics: Analgesia; Animals; Dizocilpine Maleate; Formaldehyde; Injections, Subcutaneous; Male; Mice; Naloxone; Pain; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Stress, Physiological; Time Factors

The hyperalgesia and spontaneous pain that occur following peripheral nerve injury may be related to abnormal peripheral input or altered central activity, or both. The present experiments investigated these possibilities by examining the effects of MK-801 (a non-competitive N-methyl-D-aspartate, NMDA, receptor antagonist) and bupivacaine (a local anesthetic agent) on thermal hyperalgesia and spontaneous nociceptive behaviors in rats with painful peripheral mononeuropathy. Peripheral mononeuropathy was produced by loosely ligating the rat's common sciatic nerve, a procedure which causes chronic constrictive injury (CCI) of the ligated nerve. The resulting hyperalgesia to radiant heat and spontaneous nociceptive behaviors was assessed by using a foot-withdrawal test and a spontaneous pain behavior rating method, respectively. CCI rats receiving 4 daily intraperitoneal (i.p.) MK-801 injections (0.03, 0.1, 0.3 mg/kg) beginning 15 min prior to nerve ligation exhibited less hyperalgesia (i.e., longer foot-withdrawal latencies) on days 3, 5, 7, 10, and 15 after nerve ligation as compared to those receiving saline injections. Thermal hyperalgesia also was reduced when a single MK-801 injection was given intrathecally (i.t.) onto the spinal cord lumbar segments on Day 3 after nerve ligation. This effect of postinjury MK-801 treatment was dose-dependent (2.5-20 nmol) and lasted for at least 48 h after injection. Moreover, i.t. injection of MK-801 (10 nmol) reliably lowered spontaneous pain behavior rating scores in CCI rats compared to those in the saline group. The spinal site of MK-801 action is situated within the caudal (probably lumbar) spinal cord, since i.t. injection of MK-801 (10 nmol) onto the spinal cord thoracic segments did not affect thermal hyperalgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Anesthesia, Local; Animals; Bupivacaine; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Nociceptors; Pain; Peripheral Nervous System Diseases; Rats; Rats, Inbred Strains; Sciatic Nerve; Spinal Cord; Time Factors

Rats were stereotaxically implanted with microinjection cannulae aimed at sites ranging caudally from the lower medulla and rostrally to the diencephalon and received microinjections of the excitatory amino acid: L-glutamate 30 nmol/0.5 microliters. The subsequent spontaneous behavioral response and the effect on the thermal noxious-evoked tail flick (TF) and hot plate (HP) responses was recorded. From 331 brain sites mapped with glutamate, an elevation of tail flick and hot plate response latencies was observed in 59 cases and in 34 of these sites the antinociceptive activity was preceded by a shortlasting aversion characterized by vocalization and running. The glutamate-sensitive sites at which TF and HP response latencies were elevated were exclusively distributed in the medullary reticular formation (MRF) and the mesencephalic periaqueductal gray matter (PAG). The aversive and antinociceptive activity of glutamate was dose-dependent and mimicked by the excitatory amino acid (EAA) receptor agonists N-methyl-D-aspartate + (NMDA) kainate and less so quisqualate. The EAA receptor antagonists MK-801 and AP-5, but not glutamyl-amino-methyl-sulfonic acid, antagonized in a dose-dependent fashion both the aversive and antinociceptive responses evoked from the PAG. It is suggested that NMDA receptor-linked neurons in the PAG activate both nociceptive and antinociceptive systems.

Topics: 2-Amino-5-phosphonovalerate; Animals; Brain Mapping; Brain Stem; Diencephalon; Dizocilpine Maleate; Female; Glutamates; Glutamic Acid; Kainic Acid; Male; Medulla Oblongata; Mesencephalon; Microinjections; N-Methylaspartate; Pain; Periaqueductal Gray; Quisqualic Acid; Rats; Rats, Inbred Strains; Reticular Formation; Stereotaxic Techniques

Central activation of excitatory amino acid receptors has been implicated in neuropathic pain following nerve injury. In a rat model of painful peripheral mononeuropathy, we compared the effects of non-competitive NMDA receptor antagonists (MK 801 and HA966) and a non-NMDA receptor antagonist (CNQX) on induction and maintenance of thermal hyperalgesia induced by chronic constrictive injury (CCI) of the rat common sciatic nerve. Thermal hyperalgesia to radiant heat was assessed by using a foot-withdrawal test and NMDA/non-NMDA receptor antagonists were administered intrathecally onto the lumbar spinal cord before and after nerve injury. Four daily single treatments with 20 nmol HA966 or CNQX beginning 15 min prior to nerve ligation (pre-injury treatment), reliably reduced thermal hyperalgesia in CCI rats on days 3, 5, 7 and 10 after nerve ligation. Thermal hyperalgesia was also reduced in CCI rats receiving a single post-injury treatment with HA966 (20 or 80 nmol) or MK 801 (5 or 20 nmol) on day 3 after nerve ligation when thermal hyperalgesia was well developed. In contrast, a single post-injury CNQX (20 or 80 nmol) treatment failed to reduce thermal hyperalgesia or to potentiate effects of HA966 or MK 801 (5 or 20 nmol) on thermal hyperalgesia in CCI rats. Moreover, multiple post-injury CNQX treatments utilizing the same dose regime as employed for the pre-injury treatment attenuated thermal hyperalgesia but only when the treatment began 1 or 24 h (but not 72 h) after nerve ligation.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dizocilpine Maleate; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Pain; Peripheral Nervous System Diseases; Pyrrolidinones; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Sciatic Nerve

The effects of the specific N-methyl-D-aspartic acid (NMDA) receptor antagonist MK-801 (dizocilpine, 0.075 mg/kg, i.p.) on swim-stress-induced analgesia (SSIA) were studied in control (C) mice and in mice selectively bred for high (HA) or low (LA) SSIA. In three consecutive experiments, animals were subjected to forced swimming at water temperature of 20 degrees C, 32 degrees C and 15 degrees C and the resulting analgesia (hot-plate test) was found to be mixed opioid/non-opioid, opioid and non-opioid, respectively, as a function of the degree of antagonism by naloxone (10 mg/kg, i.p.). The major finding of this study is that MK-801 attenuated 15 degrees C SSIA, against which naloxone was ineffective, but had no effect on 32 degrees C SSIA, which naloxone blocked completely. A combination of naloxone and MK-801 significantly attenuated 20 degrees C SSIA in C and HA mice and in HA mice this attenuation was significantly larger than that produced by either drug alone. Morphine analgesia (10 mg/kg, i.p.) was unaffected by MK-801. It is concluded that low doses of MK-801 selectively block non-opioid mechanisms of SSIA.

Topics: Analgesia; Animals; Dizocilpine Maleate; Female; Male; Mice; Mice, Inbred Strains; Morphine; Naloxone; Pain; Receptors, N-Methyl-D-Aspartate; Stress, Psychological; Swimming

The analgesic effect of a 3-min swim stress was assessed using the formalin test. Male Swiss mice were injected i.p. with naloxone (0.1 or 1.0 mg/kg), MK-801 (0.075 mg/kg) or saline 15 min prior to swimming in water maintained at 20 degrees C or 32 degrees C. The mice were then injected with 20 microliters of 5% formalin into the plantar surface of 1 hind paw and pain behaviour (time spent licking the injected paw) was continuously monitored during the subsequent 10 min. Swim stress produced a significant reduction in pain behaviour at both 20 degrees C and 32 degrees C. MK-801 completely blocked the analgesia produced by both the 20 degrees C and 32 degrees C swim. At a dose of 0.1 mg/kg, naloxone partially antagonized the analgesia produced by the 32 degrees C swim but did not affect the analgesia produced by the 20 degrees C swim. Naloxone at a dose of 1.0 mg/kg had no effect on swim stress-induced analgesia. Neither MK-801 nor 0.1 mg/kg naloxone altered baseline pain behaviour, although 1.0 mg/kg naloxone did significantly reduce it. It is unlikely that the effect of MK-801 on swim stress-induced analgesia is due to an interaction with an opioid mechanism, as MK-801 had no effect on morphine analgesia. These results suggest that the analgesia produced by the 20 degrees C swim stress in the formalin test is non-opioid in nature and mediated via the NMDA receptor, whereas the 32 degrees C swim stress-induced analgesia has both an opioid and non-opioid component.

Topics: Analgesia; Animals; Dizocilpine Maleate; Formaldehyde; Male; Mice; Mice, Inbred Strains; Morphine; Naloxone; Pain; Receptors, N-Methyl-D-Aspartate; Sensation; Stress, Physiological

Current thinking emphasizes that protracted small afferent input can evoke mechanisms that mediate a significant potentiation of spinal nociceptive processing and that this facilitory component has a unique pharmacology. To investigate the behavioral parallels of this spinal facilitation, we evaluated the effects of pre- and post-treatment of intrathecal morphine (mu agonist) and MK801 (N-methyl-D-aspartate [NMDA] antagonist) on the formalin test. Intraplantar formalin resulted in a biphasic appearance of flinching behavior (phase 1 = 0-5 min; phase 2 = 10-60 min). Morphine and MK801 were administered intrathecally 15 min before formalin injection in the pretreatment study and 9 min after formalin injection in the posttreatment study. Pretreatment with intrathecal morphine produced comparable dose-dependent suppressions of the phase 1 and phase 2 behaviors (ED50 = 0.5 micrograms [95% CI = 0.3-0.9] and 0.3 micrograms [95% CI = 0.1-0.7], respectively). Posttreatment with morphine also resulted in comparable suppression of the phase 2 response (ED50 = 0.2 micrograms [95% CI = 0.1-0.3]). At the highest dose of intrathecal morphine (10 micrograms), an almost complete suppression of formalin-evoked behavior was observed. Pretreatment with MK801 inhibited the second-phase response more strongly than the first-phase response (ED50 = 1.6 micrograms [95% CI = 0.5-5.7] vs. 0.1 microgram [95% CI = 0.3 - 0.4], respectively). In contrast, posttreatment with the highest dose of MK801 had no effect on the phase 2 response.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Dizocilpine Maleate; Injections, Spinal; Male; Morphine; N-Methylaspartate; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Time Factors

The involvement of NMDA receptors in rats with peripheral inflammation and hyperalgesia was evaluated by administration of the non-competitive NMDA receptor antagonist, MK-801. Inflammation and hyperalgesia was induced by intradermal injection of complete Freund's adjuvant (CFA) or carrageenan into the left hind paw. The latency of paw withdrawal from a thermal stimulus was used as a measure of hyperalgesia in awake rats. MK-801 (1.6 mg/kg, i.p., or 31.5 micrograms, intrathecal) significantly attenuated thermal hyperalgesia and reduced its duration in comparison to saline-injected rats (P less than 0.05). The receptive field size of nociceptive-specific and wide-dynamic-range neurons in the superficial and deep spinal dorsal horn recorded 24 h after injection of CFA was significantly reduced to 73 +/- 6% (P less than 0.05, n = 8) and 74 +/- 4% (P less than 0.05, n = 8) of control values, respectively, by a cumulative dose of 3 mg/kg of MK-801 (i.v.). MK-801 (2 mg/kg) prevented the expansion of the receptive fields of dorsal horn neurons recorded 5 +/- 0.4 h (n = 5) after intradermal injection of CFA as compared to saline-injected rats (P less than 0.05). MK-801 had no significant effect on receptive field size of dorsal horn neurons in rats without CFA-induced inflammation but blocked a transient expansion of the receptive fields induced by 1 Hz, C-fiber intensity electrical stimulation of the sciatic nerve. The background activity and noxious heat-evoked response of dorsal horn neurons in rats with CFA-induced inflammation were primarily inhibited and noxious pinch-evoked activity was both facilitated and inhibited by the administration of MK-801. These results support the hypothesis that NMDA receptors are involved in the dorsal horn neuronal plasticity and behavioral hyperalgesia that follows peripheral tissue inflammation.

Topics: Animals; Behavior, Animal; Dizocilpine Maleate; Electric Stimulation; Freund's Adjuvant; Hyperalgesia; Male; Myelitis; Neurons; Pain; Physical Stimulation; Rats; Spinal Cord

Protection by the NMDA receptor antagonist MK-801 against transient spinal cord ischemia-induced hypersensitivity was studied in rats. The spinal ischemia was initiated by vascular occlusion resulting from the interaction between the photosensitizing dye Erythrosin B and an argon laser beam. The hypersensitivity, termed allodynia, where the animals reacted by vocalization to nonnoxious mechanical stimuli in the flank area, was consistently observed during several days after induction of the ischemia. Pretreatment with MK-801 (0.1-0.5 mg/kg, iv) 10 min before laser irradiation dose dependently prevented the occurrence of allodynia. The neuroprotective effect of MK-801 was not reduced by maintaining normal body temperature during and after irradiation. There was a significant negative correlation between the delay in the administration of MK-801 after irradiation and the protective effect of the drug. Histological examination revealed slight morphological damage in the spinal cord in 38% of control rats after 1 min of laser irradiation without pretreatment with MK-801. No morphological abnormalities were observed in rats after pretreatment with MK-801 (0.5 mg/kg). The present results provide further evidence for the involvement of excitatory amino acids, through activation of the NMDA receptor, in the development of dysfunction following ischemic trauma to the spinal cord.

Topics: Amino Acids; Animals; Dizocilpine Maleate; Female; Ischemia; Lasers; Nervous System Diseases; Pain; Radiation Injuries, Experimental; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Sensation; Sensory Thresholds; Spinal Cord

The effects of the specific N-methyl-D-aspartic acid (NMDA) receptor antagonist MK-801 (0.075 mg/kg), and the specific opiate receptor antagonist naloxone (10 mg/kg), on swim stress-induced analgesia (SSIA) were studied in opiate receptor-deficient (CXBK) and opiate receptor-rich (CXBH) mice. Animals were subjected to forced swimming, and analgesia was assessed using the hot-plate test. In CXBK mice SSIA was blocked by MK-801 but was completely insensitive to naloxone. In CXBH mice SSIA was partially attenuated both by naloxone and MK-801, and it was nearly abolished by a combination of these drugs. Morphine analgesia (10 mg/kg) was abolished by naloxone but completely unaffected by MK-801 in CXBH mice. These findings suggest that the NMDA receptor is critically involved in the non-opioid component of SSIA.

Topics: Analysis of Variance; Animals; Dizocilpine Maleate; Male; Mice; Mice, Inbred Strains; Pain; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Sensory Thresholds; Stress, Physiological

Loose ligation of the sciatic nerve in the rat can produce behavioral signs of hyperalgesia in the hindpaw. This study examined the effect of an NMDA (N-methyl-D-aspartate) receptor antagonist (MK-801) on the development of hyperalgesia in this model. Rats received i.p. injections of saline or MK-801 (1.0 mg/kg) prior to and then for 7 days after a unilateral sciatic nerve ligation. Testing of each hindpaw for latency to withdrawal from a standardized thermal stimulus was performed prior to ligation and then at 10, 12, 17, 27, and 37 days postoperatively. Hyperalgesia of the operated hindpaw developed in saline-treated animals as measured by a decrease in withdrawal latency. Hyperalgesia did not develop in animals treated with MK-801. MK-801 may therefore prevent the development of hyperalgesia following experimental nerve injury, possibly through an NMDA receptor-mediated effect.

Topics: Animals; Dizocilpine Maleate; Hot Temperature; Hyperalgesia; Male; Pain; Peripheral Nervous System Diseases; Rats; Rats, Inbred Strains; Sciatic Nerve

In urethane-anesthetized rats, xylene applied locally to the skin of the hind paws was shown to induce reflex increases of blood pressure (33%) and heart rate (37%). The blood pressure elevation was dose dependently inhibited by the NMDA antagonist, MK-801 (0.3-1.0 mg/kg i.v.), and by the AMPA (D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxalonepropionic acid) antagonist, NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline 0.1-1.0 mg/kg per min). In contrast, only the latter compound was shown to block dose dependently the observed increase in heart rate. The results suggest that the two glutamate antagonists inhibit nociceptive impulse traffic at distinct anatomical sites and/or by different modes of actions.

Topics: Animals; Blood Pressure; Cardiovascular Physiological Phenomena; Cardiovascular System; Dizocilpine Maleate; Female; Heart Rate; Pain; Propranolol; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, AMPA; Receptors, Neurotransmitter; Reflex; Skin; Skin Physiological Phenomena

When a peripheral nerve is severed, damaged sensory fibers emit a barrage of impulses that lasts for many seconds, or even several minutes ('injury discharge'). We have shown in rats that local anesthetic blockade of this discharge suppresses autotomy (a behavioral model of neuropathic pain). Correspondingly, mimicking prolonged injury discharge with electrical stimulation, especially of C-fibers, increased autotomy. These data support the hypothesis that injury discharge plays a role in the triggering of neuropathic pain. The mechanism of triggering autotomy was investigated using intrathecal injection of agents affecting glutamatergic transmission. A single intrathecal injection at the lumbar enlargement of the NMDA receptor blockers MK-801 and 5-APV, just prior to neurectomy, significantly suppressed autotomy. Blocking glycinergic inhibition just prior to neurectomy with a single strychnine injection strikingly enhanced autotomy. Strychnine enhancement of autotomy was prevented by prior injection of MK-801 or 5-APV. These results suggest that the expression of autotomy in rats, and by inference neuropathic pain in humans, is affected by injury discharge, possibly mediated by long-lasting, NMDA receptor-related, spinal disinhibition.

Topics: 2-Amino-5-phosphonovalerate; Animals; Behavior, Animal; Dizocilpine Maleate; Electric Stimulation; Glutamates; Glutamic Acid; Glycine; Injections, Spinal; Male; Pain; Peripheral Nerve Injuries; Rats; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Strychnine

Repetitive stimulation of small diameter primary afferent fibres produces a progressive increase in action potential discharge (windup) and a prolonged increase in the excitability of neurones in the spinal cord following the stimulus. Previous studies have demonstrated that windup is the consequence of the temporal summation of slow synaptic potentials and that the slow potentials and windup are reduced by pretreatment with N-methyl-D-aspartic acid (NMDA) antagonists. We have now examined whether primary afferent induced hypersensitivity states in flexor motoneurones are also dependent on the activation of NMDA receptors and whether windup is a possible trigger for the production of the central hypersensitivity. Both a non-competitive (MK-801) and a competitive (D-CPP) NMDA antagonist, at doses that did not modify the baseline reflex, reduced the facilitation of the flexor reflex produced by either brief electrical stimulation of the sural nerve (1 Hz for 20 sec at C-fibre strength), or by the cutaneous application of the chemical irritant mustard oil. These antagonists also prevented windup from occurring in the motoneurones. When the the MK-801 and the D-CPP were administered once a state of central facilitation had been induced by prior treatment with mustard oil, they returned the facilitated reflex to its pretreatment level. These results indicate that NMDA receptors are involved in the induction and maintenance of the central sensitization produced by high threshold primary afferent inputs. Because central sensitization is likely to contribute to the post-injury pain hypersensitivity states in man, these data have a bearing both on the potential role of NMDA antagonists for pre-emptive analgesia and for treating established pain states.

Topics: Action Potentials; Animals; Dizocilpine Maleate; Motor Neurons; Mustard Plant; Pain; Physical Stimulation; Piperazines; Plant Extracts; Plant Oils; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Reflex; Sural Nerve; Wounds and Injuries

Subcutaneous injection of formalin into the hindpaw peripheral receptive field of deep dorsal horn multireceptive (convergent) nociceptive neurones was used to produce a prolonged (1 h) activation of the cells. This chemical noxious stimulus produced a first peak of firing which lasted 10 min followed by a second peak of prolonged activity which was monitored for 50 min. gamma-D-glutamylglycine (DGG), a non-selective N-methyl-D-aspartate (NMDA) and quisqualate/kainate (non-NMDA) receptor antagonist was applied intrathecally both as a pretreatment and after the formalin. A complete abolition of both peaks of the formalin response was produced by DGG pretreatment (1000 micrograms) (n = 4). This dose produced profound inhibition of the acute C-fibre evoked responses of the same cells. However, no inhibitions were produced when the antagonist was applied once the formalin response had developed (n = 4). The selective NMDA receptor antagonist 5-amino-phosphonovaleric acid (AP5) was administered intrathecally (250 and 500 micrograms) as a 40 min pretreatment and caused a small inhibition of the first peak but a marked dose-related reduction in the second prolonged phase (n =7). AP5 did not influence the C-fibre inputs onto the cells. The non-competitive NMDA receptor channel blockers, ketamine and MK801, were administered i.v. during the second phase of firing. Ketamine (1-8 mg/kg) caused a short-lasting but marked and dose-related inhibition of the neuronal responses to formalin (n = 11). MK801 (0.5-1 mg/kg) resulted in a prolonged inhibition of cell firing during the second phase of the response (n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Amino-5-phosphonovalerate; Animals; Dibenzocycloheptenes; Dipeptides; Dizocilpine Maleate; Electric Stimulation; Formaldehyde; Ketamine; Neurons; Nociceptors; Pain; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Spinal Cord

Previous studies have suggested a role of excitatory amino acids (EAA) in nociception. In the present study the effects of two antagonists of EAA-receptors on capsaicin-induced eye wipings were investigated. Intracisternally administered kynurenic acid, in contrast to intravenously administered MK-801, was found to effectively block the induced eye wipings. It is proposed that EAA, by activating non-NMDA receptors, are involved in the transmission of chemogenic nociception.

Topics: Animals; Behavior, Animal; Capsaicin; Cisterna Magna; Dizocilpine Maleate; Injections; Kynurenic Acid; Male; Nociceptors; Pain; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate