2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and Pain--Postoperative

The rostral ventromedial medulla (RVM) is highly involved in pain signal transmissions. Previous studies have shown that thalidomide is anti-nociceptive. Thus, we evaluated the neurobiological mechanisms of thalidomide in the RVM in the regulation of postoperative pain. We used a rat model of postoperative pain to investigate the effects of intra-RVM thalidomide treatments on postoperative pain, and evaluate the role of cannabinoid receptors in the effects of intra-RVM thalidomide treatments on GABAergic neurotransmission in the RVM neurons. We found intra-RVM thalidomide treatments reduced incisional surgery induced mechanical allodynia. This phenomenon was associated with attenuation of the frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs) and spontaneous IPSCs (sIPSCs) in RVM neurons. Furthermore, applications of WIN 55,212-3 mesylate, a non-selective cannabinoid receptor antagonist reversed the effects of repeated thalidomide treatment on the frequency but not the amplitude of mIPSCs and sIPSCs. Finally, we found that repeated thalidomide treatment robustly enhanced CB2 receptor expression, but slightly reduced CB1 receptor expression, in the RVM. These results suggested that the antinociceptive effects of thalidomide in the RVM likely involve the attenuation of GABA release, which are critically regulated by cannabinoid receptors.

Topics: Analgesics; Animals; Disease Models, Animal; Electric Stimulation; Excitatory Amino Acid Antagonists; Hyperalgesia; Inhibitory Postsynaptic Potentials; Male; Medulla Oblongata; Neurons; Pain Measurement; Pain Threshold; Pain, Postoperative; Quinoxalines; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Tetrodotoxin; Thalidomide; Valine

Further understanding of pathophysiology of postoperative acute pain is necessary for its better management. The methodology of current threshold (CT) determination by using sine-wave stimuli at 3 frequencies has been used to selectively and quantitatively analyze the function of the subsets of fibers (i.e., frequency of 5, 250, and 2000Hz recruits C-, Adelta-, and Abeta-fibers, respectively). This study investigated how surgical incision would affect the CTs, and then assessed the efficacy of intrathecal pharmacotherapy. The CT required to evoke a paw withdrawal response was assessed over time at stimulus frequencies of 5Hz (CT5), 250Hz (CT250), and 2000Hz (CT2000) in rats that had undergone surgical incision of the plantar skin and muscle. The CTs at all frequencies significantly decreased immediately after the incision. The decreased thresholds gradually recovered during the first week post-surgery. CT5 and CT250 (but not CT2000) remained significantly low even on day 7 post-surgery. Morphine at 5microg/10microL i.t. significantly reversed CT5 and CT250. NBQX (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid [AMPA]/kainate receptor antagonist) at 1.9 or 3.8microg/10microL i.t. significantly increased the thresholds over the pre-surgery threshold levels at all frequencies. MK-801 (N-methyl d-aspartate [NMDA] receptor antagonist) up to 13.5microg/10microL i.t. did not significantly affect CTs at any frequencies. In conclusion, a broad spectrum of sensory fibers (Abeta, Adelta, and C) is sensitized at the spinal and/or peripheral level in the postoperative acute pain state. Spinal AMPA/kainate receptors but not NMDA receptors play a significant role in this sensitization.

Topics: Animals; Dizocilpine Maleate; Foot; Infusions, Parenteral; Male; Models, Animal; Morphine; Narcotics; Nerve Fibers, Myelinated; Nerve Fibers, Unmyelinated; Pain Threshold; Pain, Postoperative; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Subarachnoid Space

Secondary mechanical hyperalgesia has been demonstrated in postoperative patients indicating that central sensitization occurs after surgery. However, the underlying mechanisms are unknown. Here, we studied the role of spinal AMPA/kainate receptors for pain behaviors indicating secondary hyperalgesia caused by gastrocnemius incision in the rat. These were reduced by NBQX, a selective antagonist of AMPA/kainate receptors. However, administration of NMDA receptor antagonists caused no or only a modest decrease in behaviors for secondary hyperalgesia but produced associated motor deficits and supraspinal side effects. We further determined that only secondary mechanical hyperalgesia was reversed by JSTX, a selective antagonist of calcium-permeable AMPA receptor; primary mechanical hyperalgesia and guarding behavior were unchanged. These findings indicate that JSTX influenced a spinal amplification process that leads to secondary hyperalgesia but does not contribute to primary hyperalgesia and guarding after incision. This amplification process likely requires Ca(2) influx through spinal AMPA/KA (but not NMDA) receptors. Behaviors for secondary mechanical hyperalgesia after incision can be inhibited without affecting primary mechanical hyperalgesia and guarding. Mechanisms for central sensitization causing secondary hyperalgesia in postoperative patients may therefore be separated from spontaneous pain and hyperalgesia that arises adjacent to the area of the incision.

Topics: Animals; Calcium; Excitatory Amino Acid Antagonists; Hyperalgesia; Male; Mechanoreceptors; Muscle, Skeletal; Neurotoxins; Pain Threshold; Pain, Postoperative; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Spider Venoms; Spinal Cord

Surgery commonly causes pain and neural plasticity that are unique compared to other persistent pain problems. To more precisely study central sensitization and plasticity, we examined the role of ionotropic EAA receptors in dorsal horn neuron sensitization early after incision. Sensitization, in the form of increased background activity, increased mechanosensitivity or pinch receptive field expansion, was induced by plantar incision 1 h later in 30 neurons. (+)-5-Methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine (MK-801) or 1 mM 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo[f]quinoxaline-7-sulfonamide (NBQX) was administered through a microdialysis fiber to block NMDA and nonNMDA EAA receptors, respectively. Dorsal horn neuron sensitization was reexamined 1 h later. Spinal administration of NBQX blocked AMPA-induced excitation but did not affect excitation by NMDA. NBQX decreased background activity in the neurons that developed sustained increased activity after incision. The median decrease caused by NBQX was from 2.3 to 0.0 imp/s. Spinal administration of 5 mM MK-801 blocked NMDA-induced excitation but did not affect excitation by AMPA. The median change (from 2.6 to 1.1 imp/s) in background activity increased by incision was not significantly affected by MK-801. The responses to mechanical stimuli were enhanced after incision in wide dynamic range (WDR) neurons. NBQX eliminated these responses but MK-801 had no effect. The pinch receptive field (RF) expansion into uninjured areas of the paw and hindquarters occurred after incision. Only 1 of 13 neurons exhibited RF expansion after spinal NBQX administration; 9 of 12 neurons had RF expansion remaining after MK-801. Thus, nonNMDA receptors are critical and NMDA-independent factors influence the increased responsiveness of dorsal horn neurons that occur early after incision.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Male; N-Methylaspartate; Neuronal Plasticity; Pain, Postoperative; Physical Stimulation; Posterior Horn Cells; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Postoperative pain significantly impacts patient recovery. However, postoperative pain management remains suboptimal, perhaps because treatment strategies are based mainly on studies using inflammatory pain models. We used a recently developed mouse model of incisional pain to investigate peripheral and spinal mechanisms contributing to heat hyperalgesia after incision. Behavioral experiments involving TRPV1 KO mice demonstrate that, as previously observed in inflammatory models, TRPV1 is necessary for heat (but not mechanical) hyperalgesia after incision. However, in WT mice, neither the proportion of TRPV1 immunoreactive neurons in the DRG nor the intensity of TRPV1 staining in the sciatic nerve was different from that in controls up to 4 days after incision. This result was corroborated by immunoblot analysis of sciatic nerve in rats subjected to an incision, and is distinct from that following inflammation of the rat hind paw, a situation in which TRPV1 expression levels in sciatic nerve increases. In the absence of heat exposure, spinal c-Fos staining was similar between incised TRPV1 KO and WT mice. However, differences in c-Fos staining between heat exposed TRPV1 KO and WT mice after incision suggest that the incision-mediated enhancement of heat-evoked signaling to the spinal cord involves a TRPV1-dependent mechanism. Finally, heat hyperalgesia after incision was reversed by antagonism of spinal non-NMDA receptors, unlike inflammatory hyperalgesia, which is mediated via NMDA receptors . Thus, TRPV1 is important for the generation of thermal hyperalgesia after incision. Our observations suggest that all experimental pain models may not be equally appropriate to guide the development of postoperative pain therapies.

Topics: Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Hot Temperature; Hyperalgesia; Ion Channels; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurogenic Inflammation; Nociceptors; Pain, Postoperative; Physical Stimulation; Proto-Oncogene Proteins c-fos; Quinoxalines; Skin; TRPV Cation Channels

Secondary mechanical hyperalgesia has been demonstrated in postoperative patients indicating that central sensitization occurs after surgery. However, the underlying mechanisms are unknown. Here, we studied the role of spinal N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate receptors for pain behaviors indicating secondary hyperalgesia caused by gastrocnemius incision in the rat. We further determined if Ca(2+) permeable AMPA/kainate receptors are important for secondary hyperalgesia after gastrocnemius incision and for pain behaviors indicating primary hyperalgesia and guarding behavior after plantar incision. Withdrawal thresholds (WTs) to punctate mechanical stimuli were assessed by applying calibrated monofilaments to the plantar hind paw before gastrocnemius incision. WTs were tested again 2 h after gastrocnemius incision and again after intrathecal (IT) injection of either dizocilpine maleate (MK-801), 2-amino-5-phosphonovaleric acid (AP5), 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo[f]quinoxaline-7-sulfonamide (NBQX), or Joro spider toxin (JSTX). The doses used were: MK-801 (vehicle, 15, 30, 40 nmol), AP5 (vehicle, 10, 30 nmol), NBQX (vehicle, 5, 10 nmol), and JSTX (vehicle, 2, 5, 9 nmol). In the same rats, WTs were tested on postoperative day 2 before and after the same drugs were injected again. In other rats, WTs to monofilaments and response frequencies to a non-punctate mechanical stimulus or guarding behaviors were determined before, 1 h after plantar incision was made, and assessed again after JSTX (9 nmol or vehicle) was administered IT. Secondary mechanical hyperalgesia after gastrocnemius incision was dose-dependently blocked by NBQX but was only marginally affected by AP5 or MK-801. Only secondary mechanical hyperalgesia was reversed by JSTX; primary mechanical hyperalgesia and guarding behavior were unchanged. These results indicate that spinal sensitization contributing to behaviors for secondary hyperalgesia after incision requires Ca(2+) permeable AMPA/kainate receptors. The data further demonstrate that behaviors for secondary mechanical hyperalgesia after incision can be inhibited without affecting behaviors for primary mechanical hyperalgesia and guarding. Mechanisms for central sensitization causing secondary hyperalgesia in postoperative patients may therefore be separated from spontaneous pain and hyperalgesia that arises adjacent to the area of the incision.

Topics: Animals; Behavior, Animal; Diagnosis, Differential; Excitatory Amino Acid Antagonists; Foot; Hyperalgesia; Male; Muscle, Skeletal; Neurotoxins; Pain Threshold; Pain, Postoperative; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Spider Venoms; Spinal Cord

Drugs that block spinal excitatory amino acid receptor activation may prevent pain after surgery. The authors previously studied the effect of excitatory amino acid receptor antagonists after incision. In the present study, we examined the role of N-methyl-d-aspartate (NMDA), non-NMDA, and metabotropic glutamate receptors (mGluRs) on the development of pain behavior after plantar incision.. Rats with lumbar intrathecal catheters were anesthetized with halothane. Fifteen minutes before an incision was made, drug [40 nmol MK-801; 20 nmol NBQX; or 200 nmol (+)-MCPG] or vehicle was injected intrathecally followed by an infusion of the same drug for 75 min. Withdrawal thresholds to calibrated von Frey filaments applied adjacent to the wound and response frequencies to a blunt mechanical stimulus applied directly to the wound were measured before incision and 1, 2, 4, and 6 h after incision and then once daily for 6 days.. Preincision treatments with antagonists against the NMDA (MK-801) and group I and II metabotropic receptors [(+)-MCPG] did not inhibit the development of mechanical hyperalgesia caused by incision. Preincision treatment with the non-NMDA receptor antagonist NBQX increased withdrawal thresholds at 1 and 2 h and on postoperative day 1 compared with the vehicle group; response frequencies were reduced 1 and 2 h after incision and on postoperative day 2 (P < 0.05). In an additional group, postincision treatment with NBQX was similar to preincision treatment.. Spinal NMDA and mGluR antagonists may not be useful for preventing postsurgical pain. Spinal non-NMDA receptor antagonists reduced pain behaviors, but a preventive effect using preincision treatment was not apparent.

Topics: Analgesia; Anesthesia, Inhalation; Anesthetics, Inhalation; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Foot; Halothane; Injections, Spinal; Male; Motor Activity; Pain, Postoperative; Quinoxalines; Rats; Rats, Sprague-Dawley

Evidence indicates that excitatory amino acids (EAAs) like glutamate and aspartate are important in the processing of nociceptive information in the dorsal horn of the spinal cord. Recently, the role of particular EAA receptors in pain transmission and facilitated pain states has been examined utilizing spinal administration of specific receptor antagonists. Most investigators have studied the involvement of N-methyl-D-aspartate (NMDA) EAA receptors in hyperalgesia and nociception; less is known about the importance of non-NMDA EAA receptors in animal models of persistent pain. To study the role of spinal non-NMDA EAA receptors in pain behaviors caused by an incision, we examined the effect of i.t. administered non-NMDA EAA receptor antagonists in a rat model of postoperative pain. Rats with i.t. catheters were anesthetized and underwent a plantar incision. Withdrawal threshold to punctate stimulation applied adjacent to the wound using von Frey filaments, response frequency to application of a non-punctate stimulus applied directly to the wound and non-evoked pain behaviors were measured before and after administration of i.t. 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo[f]quinoxaline-7-sulfonamide (NBQX), 6,7-dinitroquinoxaline-2,3-dione (DNQX), or vehicle. A separate group of animals were also tested for motor impairment caused by these drugs. In the vehicle-treated group, the median withdrawal threshold for punctate hyperalgesia decreased from 522 mN before surgery to 39 mN 2 h later; hyperalgesia was persistent. Intrathecal administration of 5 or 10 nmol of NBQX returned the withdrawal threshold toward preincision values; the median withdrawal thresholds were 158 and 360 mN, respectively. Intrathecal administration of 10 nmol of DNQX similarly increased the withdrawal threshold after incision. In separate groups of animals, i.t. administration of 5 or 10 nmol of NBQX decreased the response frequency to a non-punctate stimulus applied directly to the incision from 100+/-0% 2 h after surgery to 22+/-11 and 0+/-0% 30 min after drug injection, respectively. Similar results were observed with i.t. administration of 10 nmol of DNQX. Intrathecal NBQX also inhibited non-evoked pain behavior. In conclusion, non-NMDA receptor antagonists produced a marked decrease in pain behaviors in this model of postoperative pain. Thus, non-NMDA receptors are important for the maintenance of short-term pain behaviors caused by an incision and drugs blocking these receptors may be

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Hyperalgesia; Injections, Spinal; Male; Motor Activity; Nociceptors; Pain, Postoperative; Physical Stimulation; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Amino Acid; Receptors, Metabotropic Glutamate; Spinal Cord