dynorphins and Edema

Topics: Animals; Dynorphins; Edema; Neurons; Rats; Spinal Cord Injuries

Previous investigations from our laboratory show that up-regulation of neuronal nitric oxide synthase (NOS) following spinal cord injury (SCI) is injurious to the cord. Antiserum to dynorphin A (1-17) induces marked neuroprotection in our model of SCI, indicating an interaction between dynorphin and NOS regulation. The present investigation was undertaken to find out whether topical application of dynorphin A (1-17) antiserum has some influence on neuronal NOS up-regulation in the traumatized spinal cord. SCI was produced in anesthetized animals by making a unilateral incision into the right dorsal horn of the T10-11 segments. The antiserum to dynorphin A (1-17) was applied (1 : 20, 20 microL in 10 seconds) 5 minutes after trauma over the injured spinal cord and the rats were allowed to survive 5 hours after SCI. Topical application of dynorphin A (1-17) antiserum significantly attenuated neuronal NOS up-regulation in the adjacent T9 and T12 segments. In the antiserum-treated group, spinal cord edema and cell injury were also less marked. These observations provide new evidence that the opioid active peptide dynorphin A may be involved in the mechanisms underlying NOS regulation in the spinal cord after injury, and confirms our hypothesis that up-regulation of neuronal NOS is injurious to the cord.

Topics: Animals; Antibodies; Dynorphins; Edema; Male; Neuroprotective Agents; Nitric Oxide Synthase Type I; Rats; Rats, Sprague-Dawley; Spinal Cord Injuries; Treatment Outcome; Up-Regulation

Recent clinical studies have demonstrated that when morphine is used to control pain in cancer patients, psychological dependence is not a major concern. The present study was undertaken to ascertain the modulation of psychological dependence on morphine under a chronic pain-like state in rats. The prototypical mu-opioid receptor agonist morphine (8 mg/kg, i.p.) induced a dose-dependent place preference. In the present study, we found that an inflammatory pain-like state following formalin injection significantly suppressed the morphine-induced rewarding effect. This effect was almost reversed by s.c. pretreatment with the kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI, 5 mg/kg). Furthermore, the morphine-induced increase in dopamine (DA) turnover in the limbic forebrain was significantly inhibited by treatment with formalin. This inhibition was also suppressed by pretreatment with nor-BNI. In addition, in vivo microdialysis studies clearly showed that the morphine-induced increase in the extracellular levels of DA and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in the nucleus accumbens (N.Acc.) was significantly decreased in rats that had been pretreated with formalin. This effect was in turn reversed by the microinjection of a specific dynorphin A antibody into the N.Acc. These findings suggest that the inflammatory pain-like state induced by formalin injection may have caused a sustained activation of the kappa-opioidergic system within the N.Acc., resulting in suppression of the morphine-induced rewarding effect in rats. The present study provides further evidence of the clinical usefulness of morphine in patients suffering from severe pain.

Topics: Animals; Brain Chemistry; Conditioning, Operant; Dopamine; Dynorphins; Edema; Foot; Formaldehyde; Inflammation; Limbic System; Male; Microdialysis; Microinjections; Morphine; Naltrexone; Narcotic Antagonists; Narcotics; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Reward

Neuroimmune interactions control pain through activation of opioid receptors on sensory nerves by immune-derived opioid peptides. Here we evaluate mechanisms of intrinsic pain inhibition at different stages of Freund's adjuvant-induced inflammation of the rat paw. We use immunohistochemistry and paw pressure testing. Our data show that in early (6 h) inflammation leukocyte-derived beta-endorphin, met-enkephalin and dynorphin A activate peripheral mu-, delta- and kappa-receptors to inhibit nociception. In addition, central opioid mechanisms seem to contribute significantly to this effect. At later stages (4 days), antinociception is exclusively produced by leukocyte-derived beta-endorphin acting at peripheral mu and delta receptors. Corticotropin-releasing hormone (CRH) is an endogenous trigger of these effects at both stages. These findings indicate that peripheral opioid mechanisms of pain inhibition gain functional relevance with the chronicity of inflammation.

Topics: Animals; Corticotropin-Releasing Hormone; Dynorphins; Edema; Endorphins; Enkephalin, Methionine; Freund's Adjuvant; Hindlimb; Inflammation; Injections, Subcutaneous; Leukocytes; Male; Naloxone; Pain; Pain Threshold; Rats; Rats, Wistar; Stress, Physiological; Time Factors

The possibility that nitric oxide synthase (NOS) inhibitors influence dynorphin immunoreactivity following hyperthermia was examined in a rat model using a pharmacological approach. Previous reports from our laboratory show that hyperthermia induces an upregulation of NOS in several brain regions that seems to be instrumental in causing cell injury. Recent reports suggest that nitric oxide (NO) can influence dynorphin neurotransmission in the normal brain as well as in several pathological states. Since dynorphin is neurotoxic in different animal models of brain or spinal cord injury, it may be that the peptide will contribute to the cell injury in hyperthermia. The present investigation was carried out to determine whether hyperthermia can influence dynorphin immunoreactivity in the brain, and if so, whether inhibition of NOS will influence the peptide distribution in the brain following heat stress. Rats subjected to hyperthermia at 38 degrees C for 4 h in a biological oxygen demand incubator (BOD) resulted in a marked upregulation of dynorphin immunoreactivity in several brain regions e.g., cerebral cortex, hippocampus, cerebellum and brain stem. Pretreatment of rats with two potent NOS inhibitors, L-NAME (30 mg/kg/day, i.p. for 7 days) or L-NMMA (35 mg/kg/day, i.p. for 7 days) significantly attenuated the dynorphin immunoreactivity in the brain. These drugs were also able to reduce hyperthermia induced blood-brain barrier (BBB) permeability, brain edema formation and cell injury. Taken together, our results suggest that (i). hyperthermia has the capacity to upregulate dynorphin immunoreactivity in the brain, (ii). inhibition of NOS considerably attenuates the dynorphin immunoreaction following heat stress and (iii). upregulation of dynorphin is somehow contributing to hyperthermia induced brain damage, not reported earlier.

Topics: Animals; Blood-Brain Barrier; Brain; Coloring Agents; Dynorphins; Edema; Enzyme Inhibitors; Evans Blue; Fever; Male; Neurons; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; omega-N-Methylarginine; Permeability; Rats; Rats, Sprague-Dawley

Dynorphin is a neuropeptide that is present in high quantities in the dorsal horn of the spinal cord. The peptide is actively involved in pain processing pathways. However, its involvement in spinal cord injury is not well known. Alteration in dynorphin immunoreactivity occurs following a focal trauma to the rat spinal cord. Infusion of dynorphin into the intrathecal space of the cord results in ischemia, cell damage and abnormal motor function. Antibodies to dynorphin when injected into the intrathecal space of the spinal cord following trauma improve motor recovery, reduce edema and cell changes. However, influence of dynorphin on trauma induced alteration in spinal cord bioelectrical activity is still not known. Spinal cord evoked potentials (SCEP) are good indicator of spinal cord pathology following trauma. Therefore, in present investigation, influence of dynorphin antibodies on trauma induced changes in SCEP were examined in our rat model. In addition, spinal cord edema formation, microvascular permeability disturbances and cell injury were also investigated. Our results show that topical application of dynorphin antiserum (1 : 200) two min before injury markedly attenuated the SCEP changes immediately after injury. In the antiserum treated animals, a significant reduction in the microvascular permeability, edema formation and cell injury was observed in the traumatised spinal cord. These observations suggest that (i). dynorphin is involved in the altered bioelectrical activity of the spinal cord following trauma, (ii). the peptide actively participates in the pathophysiological processes of cell injury in the spinal cord trauma, and (iii). the dynorphin antiserum has potential therapeutic value for the treatment of spinal cord injuries.

Topics: Animals; Antibodies; Blood-Brain Barrier; Capillary Permeability; Dynorphins; Edema; Evoked Potentials; Male; Neurons; Rats; Rats, Sprague-Dawley; Spinal Cord; Spinal Cord Injuries

Dynorphin A (Dyn A) is a 17-residue opioid peptide derived from prodynorphin precursors found in mammalian tissues. Removal of Tyr1 from Dyn A produces a peptide that is more potent than Dyn A in attenuating the acute phase of the inflammatory response, as measured by inhibition of heat-induced edema in the anesthetized rat's paw (exposure to 58 degrees C water for 1 min). Dyn A(2-17), however, no longer interacts with opioid receptors. It was postulated that the non-opioid anti-inflammatory actions of Dyn A(2-17) may reside in Dyn A(6-12); that is, Arg-Arg-Ile-Arg-Pro-Lys-Leu. here we report on the activities of Dyn A(6-12) analogs modified by substitutions on the N terminus, by single N-methyl substitution and by single replacement of residues by alanine. The results indicated that the minimal sequence required for an anti-edema ED50 of <1.0 micromol/kg i.v. was anisoyl-Arg6-Arg7-Xaa8-Arg9-Pro10)-Xaa11-+ ++Xaa12-NH2. A prototype, p-anisoyl-[D-Leu12] Dyn A(6-12)-NH2, with an ED50 of 0.20 micromol/kg i.v. compared to an ED50 of 0.08 micromol/kg i.v. for Dyn A(2-17), was selected for further tests of biological activity. This analog, like Dyn A(2-17), lowered blood pressure in anesthetized rats. In a model of neurogenic inflammation, produced by antidromic stimulation of the vagus in the anesthetized rat, p-anisoyl-[D-Leu12] Dyn A(6-12)-NH2, 0.23 micromol/kg i.v., attenuated the negativity of tracheal tissue interstitial pressure (Pif), which normally develops after nerve stimulation. Modulation of interstitial pressure may be the mechanistic basis for the anti-edema properties of these Dyn A(6-12) analogs.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Dynorphins; Edema; Hindlimb; Hot Temperature; Male; Peptide Fragments; Rats; Rats, Sprague-Dawley

Dynorphin A (DYN) peptides, administered into the central nervous system, have produced inconsistent analgesic actions in tests using thermal stimuli. This study examined antinociceptive effects of intravenous and intraplantar DYN-(2-17) against noxious pressure in rats with Freund's adjuvant-induced unilateral hindpaw inflammation. The effects of DYN-(2-17) were compared to those of the opioid agonists morphine. (D-Ala2,N-Methyl-Phe4,Gly-ol5)-enkephalin (DAMGO) and DYN-(1-17). Intravenous DYN-(2-17) (0.188-10 mg/kg) produced dose-dependent elevations of paw pressure thresholds in inflamed and in non-inflamed paws. These effects were similar in magnitude to those of subcutaneous morphine (2 mg/kg), at doses of 0.375-1.5 mg/kg they were significantly greater on the inflamed (right) than on the non-inflamed (left) paw, and they were not reversible by intravenous naloxone (1-10 mg/kg). Intraplantar Dyn-(2-17)(0.001-0.3 mg) was ineffective, whereas both intraplantar DYN-(1-17)(0.15-0.3 mg) and DAMGO (0.008-0.016 mg) produced dose-dependent and naloxone-reversible elevations of paw pressure thresholds. The intraplantar injection of both Dyn peptides produced a transient increase in the volume of non-inflamed paws. These findings suggest that intravenous DYN-(2-17) produces possibly centrally mediated, non-opioid antinociceptive effects against noxious pressure. At certain doses these effects are more potent in inflamed than in non-inflamed paws. In contrast to the opioid peptides DYN-(1-17) and DAMGO, DYN-(2-17) does not appear to have no peripheral antinociceptive actions.

Topics: Analgesics; Analgesics, Opioid; Animals; Dynorphins; Edema; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Foot; Inflammation; Male; Nociceptors; Peptide Fragments; Rats; Rats, Wistar

The opioid dynorphin-A (dynA) is thought to contribute to the secondary injury process following spinal cord trauma although little is known about the biochemical mechanisms involved. In the present study, we have used a combination of magnetic resonance imaging (MRI) and spectroscopy (MRS) and hindlimb motor function tests to examine the effects of intrathecal dynA infusion on rat spinal cord. Infusion of 100 nmol of dynA (1-17) caused pronounced edema development as determined by MRI at 24 h after infusion. Infusion of 100 nmol of the dynA (2-17) fragment, which does not have any activity at opiate receptors, also produced profound edema whereas 100 nmol of the low potency kappa opiate receptor ligand dynA (1-8) or artificial CSF (ACSF) did not produce any edema. Both dynA (1-17) and dynA (2-17) produced significant hindlimb motor deficits at 24 h when compared to dynA (1-8) and ACSF (P < 0.05), but the deficits in the dynA (1-17) group were significantly worse than in the dynA (2-17) treated animals (P < 0.05). Similarly, mortality in the dynA (1-17) treated animals was significantly higher than in the other groups (P = 0.002). Phosphorus MRS demonstrated that the dynA (1-17) and dynA (2-17) treated animals also had a pronounced decline in high energy phosphates in the spinal cord 24 h after infusion. We conclude that dynA contributes to spinal cord cell death by causing metabolic failure and edema development.

Topics: Analysis of Variance; Animals; Dynorphins; Edema; Energy Metabolism; Hindlimb; Infusions, Parenteral; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy; Male; Motor Activity; Rats; Rats, Sprague-Dawley; Spinal Cord Diseases

In an earlier study, dynorphin A(1-13) [Dyn A(1-13)] was shown to inhibit heat-induced edema in the anesthetized rat's paw but the potency of this action was low, with effective doses in the range of 3-4 mg/kg i.v. In this study, Dyn A and related fragments were tested. Thermal edema was elicited in anesthetized male albino rats by immersion of the hindpaw in 58 degrees C water for 1 min. The median effective dose (ED50 and 95% confidence limits) in mg/kg i.v. for inhibition of edema were: Dyn A, Dyn A(2-17), and Dyn A(1-13), 1.7 (1.2-2.4), 0.15 (0.09-0.24), and 3.2 (1.9-5.5), respectively. The ED50 values of [D-Ala2]Dyn A, [D-Ala2]Dyn A(2-17), and [D-Ala2]Dyn A(2-17)-amide were found to be 0.92 (0.40-2.10), 1.25 (0.60-2.63), and 0.65 (0.36-1.16) mg/kg i.v., respectively. Dyn A(2-17), 0.5 mg/kg i.v., also inhibited pulmonary edema produced by i.v. injection of epinephrine. The anti-edema action of Dyn A(2-17) was not blocked by naloxone, an opioid receptor antagonist, or dependent on the hypotensive action of this peptide. It is postulated that the antiedema activity of Dyn A resides in the core fragment Dyn A(6-12). Two peptides, N-acetyl-Dyn A(6-12)-amide and N-acetyl-[D-Leu12]Dyn A(6-12)-amide, were synthesized and, when tested, were effective in reducing thermal edema with ED50 values of 1.4 (0.6-3.7) and 2.2 (1.2-4.1) mg/kg i.v., respectively.

Topics: Amino Acid Sequence; Animals; Dynorphins; Edema; Hindlimb; Hot Temperature; Male; Molecular Sequence Data; Peptide Fragments; Rats; Rats, Sprague-Dawley