dynorphins and Peripheral-Nerve-Injuries

Interleukin-17 (IL-17) is involved in a wide range of inflammatory disorders and in recruitment of inflammatory cells to injury sites. A recent study of IL-17 knock-out mice revealed that IL-17 contributes to neuroinflammation and neuropathic pain after peripheral nerve injury. Surprisingly, little is known of micro-environment modulation by IL-17 in injured sites and in pathologically related neuroinflammation and chronic neuropathic pain. Therefore, we investigated nociceptive sensitization, immune cell infiltration, myeloperoxidase (MPO) activity, and expression of multiple cytokines and opioid peptides in damaged nerves of wild-type (IL-17(+/+)) and IL-17 knock-out (IL-17(-/-)) mice after partial sciatic nerve ligation. Our results demonstrated that the IL-17(-/-) mice had less behavioral hypersensitivity after partial sciatic nerve ligation, and inflammatory cell infiltration and pro-inflammatory cytokine (tumor necrosis factor-α, IL-6, and interferon-γ) levels in damaged nerves were significantly decreased, with the levels of anti-inflammatory cytokines IL-10 and IL-13, and expressions of enkephalin, β-endorphin, and dynorphin were also decreased compared to those in wild-type control mice. In conclusion, we provided evidence that IL-17 modulates the micro-environment at the level of the peripheral injured nerve site and regulates progression of behavioral hypersensitivity in a murine chronic neuropathic pain model. The attenuated behavioral hypersensitivity in IL-17(-/-) mice could be a result of decreased inflammatory cell infiltration to the injured site, resulting in modulation of the pro- and anti-inflammatory cytokine milieu within the injured nerve. Therefore, IL-17 may be a critical component for neuropathic pain pathogenesis and a novel target for therapeutic intervention for this and other chronic pain states.

Topics: Animals; Behavior, Animal; beta-Endorphin; Central Nervous System Sensitization; Cytokines; Disease Models, Animal; Dynorphins; Enkephalins; Hyperalgesia; Inflammation; Interleukin-10; Interleukin-13; Interleukin-17; Interleukin-1beta; Interleukin-2; Interleukin-6; Macrophages; Mice; Mice, Inbred C57BL; Mice, Knockout; Neuralgia; Neutrophils; Nociception; Peripheral Nerve Injuries; Peroxidase; Sciatic Nerve; T-Lymphocytes; Tumor Necrosis Factor-alpha

The Fischer 344 (F344) rat strain differs from the Lewis strain in the response to neuropathic pain. Recently, we found that F344 rats totally recover from mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve 28 days after surgery whereas Lewis rats are initiating their recovery at this time point. Thus, the use of this neuropathic pain model in these different rat strains constitutes a good strategy to identify possible target genes involved in the development of neuropathic pain. Since differences between Lewis and F344 rats in their response to pain stimuli in acute pain models have been related to differences in the endogenous opioid and noradrenergic systems, we aimed to determine the levels of expression of key genes of both systems in the spinal cord and dorsal root ganglia (DRG) of both strains 28 days after CCI surgery. Real time RT-PCR revealed minimal changes in gene expression in the spinal cord after CCI despite the strain considered, but marked changes in DRG were observed. A significant upregulation of prodynorphin gene expression occurred only in injured DRG of F344 rats, the most resistant strain to neuropathic pain. In addition, we found a significant downregulation of tyrosine hydroxylase and proenkephalin gene expression levels in both strains whereas delta-opioid receptor was found to be significantly downregulated only in injured DRG of Lewis rats although the same trend was observed in F344 rats. The data strongly suggest that dynorphins could be involved in strain differences concerning CCI resistance.

Topics: Animals; Chronic Disease; Denervation; Disease Models, Animal; Down-Regulation; Dynorphins; Enkephalins; Ganglia, Spinal; Gene Expression Regulation; Hyperalgesia; Ligation; Male; Neurons, Afferent; Norepinephrine; Peripheral Nerve Injuries; Peripheral Nerves; Peripheral Nervous System Diseases; Protein Precursors; Rats; Rats, Inbred F344; Rats, Inbred Lew; Receptors, Opioid, delta; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Species Specificity; Spinal Cord; Tyrosine 3-Monooxygenase

Several experimental models of peripheral neuropathy show that a significant upregulation of spinal dynorphin A and its precursor peptide, prodynorphin, is a common consequence of nerve injury. A genetically modified mouse strain lacking prodynorphin does not exhibit sustained neuropathic pain after nerve injury, supporting a pronociceptive role of elevated levels of spinal dynorphin. A null mutation of the gamma isoform of protein kinase C (PKCgamma KO [knockout]), as well as an inbred mouse strain, 129S6, also does not manifest behavioral signs of neuropathic pain following peripheral nerve injury. The objective of this study was to extend our observations to these genetic models to test the hypothesis that elevated levels of spinal dynorphin are essential for the maintenance of abnormal pain. In PKCgamma wild-type mice and the outbred mouse strain ICR, ligation of the L5 and L6 spinal nerves (SNL) elicited both tactile hypersensitivity and thermal hyperalgesia. Both strains showed a significant elevation in dynorphin in the lumbar spinal dorsal horn following SNL. Spinal administration of an anti-dynorphin A antiserum blocked the thermal and tactile hypersensitivity in both strains of mice. However, the PKCgamma KO mice and the 129S6 mice (which express PKCgamma) did not show abnormal pain after SNL; neither strain showed elevated levels of spinal dynorphin. The multiple phenotypic deficits in PKCgamma KO mice confound the interpretation of the proposed role of PKCgamma-expressing spinal neurons in neuropathic pain states. Additionally, the data show that the regulation of spinal dynorphin expression is a common critical feature of expression of neuropathic pain.

Topics: Animals; Dynorphins; Male; Mice; Mice, Inbred ICR; Mice, Knockout; Pain Measurement; Peripheral Nerve Injuries; Peripheral Nerves; Peripheral Nervous System Diseases; Protein Kinase C; Species Specificity; Spinal Cord; Up-Regulation

The co-administration of morphine at spinal (i.th.) and supraspinal (i.c.v.) sites to the same rat produces antinociceptive synergy, a phenomenon which may underlie the clinical analgesic utility of this drug. In animals with peripheral nerve injury, however, the antinociceptive potency and efficacy of i.th. morphine is significantly decreased. Here, the possible loss of spinal/supraspinal morphine antinociceptive synergy and relationship to elevation of spinal dynorphin content was studied. Ligation of lumbar spinal nerves resulted in elevated dynorphin in the ipsilateral lumbar and sacral spinal cord. In sham-operated rats supraspinal/spinal co-administration of morphine produced synergistic antinociception which was unaffected by i.th. MK-801 or dynorphin A((1-17)) antiserum. In nerve-injured rats, i.th. morphine was inactive against tactile allodynia and showed diminished in potency against acute nociception without supraspinal/spinal antinociceptive synergy. Antiserum to dynorphin A((1-17)) or the non-competitive NMDA antagonist MK-801 increased the antinociceptive potency of i.th. morphine, restored supraspinal/spinal morphine antinociceptive synergy and elicited a dose-related i.th. morphine antiallodynic action. These agents did not demonstrate antinociceptive or antiallodynic activity alone and did not alter morphine actions in sham-operated animals. The loss of spinal/supraspinal antinociceptive synergy and lack of antiallodynic activity of spinal morphine appear to be due to the elevation across multiple spinal segments of dynorphin following nerve injury. Pathological actions of elevated dynorphin may directly or indirectly modulate the NMDA receptor, result in a loss of supraspinal/spinal morphine synergy and may thus account for the decreased clinical analgesic efficacy of morphine in peripheral neuropathies.

Topics: Analgesics, Opioid; Animals; Dizocilpine Maleate; Drug Synergism; Dynorphins; Excitatory Amino Acid Antagonists; Immune Sera; Injections, Intraventricular; Injections, Spinal; Male; Morphine; Neuralgia; Pain Measurement; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Touch

The development of chronically painful states following peripheral nerve injury may involve different mechanisms depending on the nature and extent of the nerve lesion. The altered spinal neurochemistry of two substances, the excitatory amino acid glutamate operating via the N-methyl-D-aspartate receptor and the endogenous opioid peptide dynorphin, have been implicated in behavioral sequelae that follow partial peripheral nerve injury. In addition, dynorphin has nonopioid functions which may involve the N-methyl-D-aspartate receptor. We investigated two hypotheses: that the development of mechanical allodynia following complete nerve injury is not greatly influenced by the N-methyl-D-aspartate receptor, and that spinal dynorphin and glutamate expression is interdependent. These studies employed sciatic cryoneurolysis, a complete but transient peripheral nerve injury that results in a delayed mechanical allodynia beginning 21-28 days after injury. Rats were administered dizocipline maleate (MK-801) at 0.25 mg/kg twice per day intraperitoneally from days 0-7 or from days 0-21 post-lesion to pre-emptively block the N-methyl-D-aspartate receptor. In a separate group of rats, an antibody to dynorphin was administered intraperitoneally at 16.6 mg/kg twice per day from days 14 to 21 post-lesion. For all groups, the outcome of allodynia behavior was assessed using von Frey filaments at 42 days post-lesion and the resulting dynorphin and glutamate immunoreactivity in the substantia gelatinosa was measured using proportional area stained and relative optical density, respectively. Only the 0-7 day MK-801 treatment increased the resulting mechanical thresholds significantly (mean +/- S.E.M. 7.0 +/- 1.2 g) when compared to saline-injected animals (3.9 +/- 0.6 g). However, this effect did not prevent allodynia since baseline thresholds were 12 or 15 g for each group. With regard to resulting spinal immunoreactivity, anti-dynorphin antibody treatment significantly increased glutamate immunoreactivity when compared to saline-treated animals (mean relative optical density +/- S.E.M. = 807.2 +/- 3.6 versus 779.6 +/- 8.3, respectively; P = 0.01) at 42 days post-lesion. We conclude that the development of allodynia following sciatic cryoneurolysis peripheral nerve injury involved a minimal contribution from N-methyl-D-aspartate receptor activity. In addition, this study demonstrated that decreasing available dynorphin using antiserum had a significant and lasting effect on

Topics: Animals; Blood-Brain Barrier; Dizocilpine Maleate; Dynorphins; Excitatory Amino Acid Antagonists; Glutamic Acid; Hyperalgesia; Immunohistochemistry; Male; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, kappa; Sciatic Nerve; Spinal Cord