Site Of Peripheral Nerve Injury Research Articles

Comparison of vibration perception thresholds in individuals with diffuse upper limb pain and carpal tunnel syndrome

The study objective was to compare vibration perception and patterns of blood flow in outpatients with diffuse upper limb pain disorder (ULPD), carpal tunnel syndrome (CTS) and age and sex matched healthy controls. Vibration perception and discrimination thresholds were compared in subjects with ULPD ( n = 27), CTS ( n = 27) and healthy matched controls ( n = 54). Vibration measurements were taken bilaterally at three sites: (a) over the dorsum of the second and (b) fifth metacarpals and (c) the palmar aspect of the first and second metacarpals, corresponding to the innervation territories of the radial, ulnar and median nerves, respectively. Non-invasive assessments of peripheral blood flow were also performed in both limbs. When compared to healthy controls, subjects with ULPD had widespread elevation of vibration thresholds both ipsilateral and contralateral to the symptomatic limb. Subjects with CTS had similarly elevated vibration thresholds at sites both adjacent to and distant from the site of peripheral nerve injury. The responses to cold pressor testing of the upper limbs were physiologically normal in both the CTS and ULPD patient groups. Furthermore, there were no significant differences in the haemodynamic responses between the patient groups. The global elevation of vibration thresholds in subjects with both ULPD and CTS is consistent with altered central nervous system mechanisms, common to both conditions, which may be either adaptive to or maintaining the perception of pain.

α2-Adrenoceptor Stimulation Transforms Immune Responses in Neuritis and Blocks Neuritis-Induced Pain

Neuropathic pain may be primarily driven by immune responses in peripheral nerves. Peripherally released catecholamines may exacerbate neuropathic pain and also modulate immune responses in a complex and sometimes opposing manner by actions on multiple adrenoceptor subtypes. We showed previously that injection of the alpha2-adrenoceptor agonist clonidine at the site of peripheral nerve injury reduces pain behavior and local tissue pro-inflammatory cytokine content in rats. The current study used a model of acute inflammatory neuritis to test the efficacy and mechanisms of action of alpha2-adrenoceptor stimulation to reduce pain. Zymosan, injected on the sciatic nerve, caused hypersensitivity to mechanical stimuli ipsilateral to injection and contralaterally, so-called mirror image pain. Ipsilateral hypersensitivity was inhibited dose-dependently by perineural injection of clonidine. Zymosan increased leukocyte number at the site of injection 3 d later as well as their content of interleukin 1alpha (IL-1alpha), IL-1beta, and IL-6. Perineural clonidine prevented both the increase in leukocyte number and cytokine expression induced by zymosan. Additionally, clonidine reduced the capacity of leukocytes to express pro-inflammatory cytokines as assessed by treatment of cells ex vivo with lipopolysaccharide, whereas no repression of IL-10 production occurred. Clonidine reduced the number of macrophages and lymphocytes as well as their expression of tumor necrosis factor alpha. All of the effects of clonidine were prevented by coadministration of an alpha2A-adrenoceptor-preferring antagonist. These results suggest that alpha2-adrenoceptor stimulation transforms cytokine gene expression, especially in macrophages and lymphocytes from a pro- to an anti-inflammatory profile in the setting of neuritis, likely relieving neuritis-induced pain by this mechanism.

Perineural alpha(2A)-adrenoceptor activation inhibits spinal cord neuroplasticity and tactile allodynia after nerve injury.

Nerve injury in animals increases alpha(2)-adrenoceptor expression in dorsal root ganglion cells and results in novel excitatory responses to their activation, perhaps leading to the phenomenon of sympathetically maintained pain. In contrast to this notion, peripheral alpha(2)-adrenoceptor stimulation fails to induce pain in patients with chronic pain. We hypothesized that alpha(2) adrenoceptors at the site of nerve injury play an inhibitory, not excitatory role. Partial sciatic nerve ligation was performed on rats, resulting in a reduction in withdrawal threshold to tactile stimulation. Animals received perineural injection at the injury site of clonidine, saline, or clonidine plus an alpha(2)-adrenergic antagonist, and withdrawal threshold was monitored. Immunohistochemistry was performed on the sciatic nerve ipsi- and contralateral to injury and on the spinal cord. Clonidine reduced this hypersensitivity in a dose-dependent manner, and this was blocked by an alpha(2A)-preferring antagonist. Perineural clonidine injection had a slow onset (days) and prolonged duration (weeks). Systemic or intrathecal clonidine, or transient neural blockade with ropivacaine, had short lasting or no effect on hypersensitivity. alpha(2A)-adrenoceptor immunostaining was increased near the site of peripheral nerve injury, both in neurons and in immune cells (macrophages and T lymphocytes). Phosphorylated cAMP response element binding protein (pCREB) in lumbar spinal cord was increased ipsilateral to nerve injury, and this was reduced 1 week after perineural clonidine injection. These data suggest that peripheral alpha(2) adrenoceptors are concentrated at the site of peripheral nerve injury, and their activation receptors produce long-lasting reductions in abnormal spinal cord gene activation and mechanical hypersensitivity.

Atypical Ganglion Cell Tumor of the Sciatic Nerve

Although herniation of a lumbosacral intervertebral disk is a major cause of sciatic distribution pain, relentlessly progressive symptoms or signs should alert one to the possibility of a tumor involving the nerve. To describe the clinical, neurophysiological, and histological features of a pathologically unique tumor involving the sciatic nerve. Tertiary referral university hospital. A 36-year-old woman was seen with a 6-year history of increasingly severe symptoms in the distribution of the left sciatic nerve. Electromyography indicated a sciatic nerve lesion in the region of the greater sciatic notch. Magnetic resonance imaging demonstrated a tumor involving the left sciatic nerve in this area. Light microscopy, electron microscopy, and immunohistochemistry results confirmed the presence of an atypical ganglion cell tumor of the sciatic nerve that exhibited prognostically conflicting clinical and histological features. To our knowledge, this is the first report of an atypical ganglion cell tumor affecting the sciatic nerve, and illustrates the value of detailed neurophysiological examination in localizing the site of peripheral nerve injury to facilitate focused neuroimaging when standard investigations are uninformative. Longer follow-up is required to determine the true biologic potential of this lesion.

Hyperalgesia due to nerve injury: role of neutrophils

The hypothesis that the early inflammatory cell, the neutrophil, contributes to the hyperalgesia resulting from peripheral nerve injury was tested in rats in which the sciatic nerve was partially transected on one side. The extent and time-course of neutrophilic infiltration of the sciatic nerve and innervated paw skin after partial nerve damage was characterized using immunocytochemistry. The number of endoneurial neutrophils was significantly elevated in sections of operated nerve compared to sections of sham-operated nerve for the entire period studied, i.e. up to seven days post-surgery. This considerable elevation in endoneurial neutrophil numbers was only observed at the site of nerve injury. Depletion of circulating neutrophils at the time of nerve injury significantly attenuated the induction of hyperalgesia. However, depletion of circulating neutrophils at day 8 post-injury did not alleviate hyperalgesia after its normal induction. It is concluded that endoneurial accumulation of neutrophils at the site of peripheral nerve injury is important in the early genesis of the resultant hyperalgesia. The findings support the notion that a neuroimmune interaction occurs as a result of peripheral nerve injury and is important in the subsequent development of neuropathic pain.

Upregulation And Interaction Of TNFα and Gelatinases A and B In Painful Peripheral Nerve Injury

Chronic constriction injury (CCI) to peripheral nerve causes a painful neuropathy in association with a process of axonal degeneration and endoneurial remodeling that involves macrophage recruitment and local increase in extracellular proteases and tumor necrosis factor alpha (TNF‐α). Cell surface activation of TNF‐α from its transmembrane precursor, as well as sequestration of TNF‐α receptors II and I, is performed by the zinc‐dependent endopeptidase family of matrix metalloproteinases (MMPs). Among TNF‐α‐converting MMPs, basal lamina degrading gelatinases are thought to play a role in sciatic nerve injury. In the present study, we determined the forms of TNF‐α involved in the development of CCI neuropathy in rats, using Western blot analysis, and the temporal correlation of TNF‐α and TNFRI protein profiles with gelatinase activity at the site of peripheral nerve injury. We observed two peaks in TNF‐α protein during the first week of CCI that correspond to previously reported peaks in painful behavior. We propose that the first peak at 6 h post‐CCI is due to the local expression of the cytotoxic transmembrane 26 kDa TNF‐α protein released by resident Schwann cells, mast cells and macrophages. This peak in TNF‐α protein expression corresponds to an increase in gelatinase B (MMP‐9) activity, which is greatly upregulated as early as 3 h following CCI to rat sciatic nerve. The second peak occurs at 5 days post‐CCI, and may represent TNF‐α protein released by hematogenously recruited macrophages. This peak is marked by the increase in active soluble 17 kDa TNF‐α and by gelatinase A (MMP‐2) upregulation. These observations suggest that there is a pathogenic role for the TNF‐α‐converting function of MMP‐2 in painful CCI neuropathy. We conclude that severe nerve injury induces MMPs, TNF‐α and TNFRI, which interactively control the privileged endoneurial environment and the pathogenesis of the painful neuropathies associated with the macrophage‐dependent processes of Wallerian degeneration.

Upregulation and interaction of TNFα and gelatinases A and B in painful peripheral nerve injury

Chronic constriction injury (CCI) to peripheral nerve causes a painful neuropathy in association with a process of axonal degeneration and endoneural remodeling that involves macrophage recruitment and local increase in extracellular proteases and tumor necrosis factor alpha (TNF-α). Cell surface activation of TNF-α from its transmembrane precursor, as well as sequestration of TNF-α receptors II and I, is performed by the zinc-dependent endopeptidase family of matrix metalloproteinases (MMPs). Among TNF-α-converting MMPs, basal lamina degrading gelatinases are thought to play a role in sciatic nerve injury. In the present study, we determined the forms of TNF-α involved in the development of CCI neuropathy in rats, using Western blot analysis, and the temporal correlation of TNF-α and TNFRI protein profiles with gelatinases activity at the site of peripheral nerve injury. We observed two peaks in TNF-α protein during the first week of CCI that correspond to previously reported peaks in painful behavior. We propose that the first peak at 6 h post-CCI is due to the local expression of the cytotoxic transmembrane 26 kDa TNF-α protein released by resident Schwann cells, mast cells and macrophages. This peak in TNF-α protein expression corresponds to an increase in gelatinase B (MMP-9) activity, which is greatly upregulated as early as 3 h following CCI to rat sciatic nerve. The second peak occurs at 5 days post-CCI, and may represent TNF-α protein released by hematogenously recruited macrophages. This peak is marked by the increase in active soluble 17 kDa TNF-α and by gelatinase A (MMP-2) upregulation. These observations suggest that there is a pathogenic role for the TNF-α-converting function of MMP-2 in painful CCI neuropathy. We conclude that severe nerve injury induces MMPs, TNF-α and TNFRI, which interactively control the privileged endoneurial environment and the pathogenesis of the painful neuropathies associated with the macrophage-dependent processes of Wallerian degeneration.

Modulation of apolipoprotein D and apolipoprotein E expression in rat hippocampus after entorhinal cortex lesion

Apolipoprotein (apo) D is a member of the lipocalin family of proteins. Although its physiological function is unknown, apoD is thought to transport one or more small hydrophobic ligands. A second apolipoprotein, apoE is known to play an important role in lipid transport, and apoE genetic polymorphism has been shown to be associated with susceptibility to Alzheimer's disease. Both apoD and apoE are expressed in the central nervous system (CNS) and both proteins accumulate at sites of peripheral nerve injury due to increased local synthesis. The two proteins may have overlapping or complementary functions within nervous tissue. In order to define the role of apoD within the CNS, we have studied the regional distribution of apoD and apoE mRNA and protein within the normal rat brain and the changes in apoD and apoE expression in the hippocampus of rats after entorhinal cortex lesion (EC lesion). Within the brains of normal rats, apoD expression in the hippocampus was as high as 180-fold that of the liver. ApoD mRNA levels in other areas of the rat brain ranged from 40 to 120 times the hepatic levels. The distribution of apoE gene expression within the brain was similar to that of apoD, but was much lower than hepatic apoE expression. When rats were subjected to EC lesion, the apoD message increased by 54% at 4 days post lesion (DPL) in the ipsilateral region of hippocampus while apoE mRNA levels (ipsilateral and contralateral) decreased by 43%. At 6 to 8 DPL apoD mRNA in the ipsilateral hippocampus remained elevated (42% above controls) whereas the apoE mRNA levels increased to about 15% above those of controls. At 14 and 31 DPL, both apoD and apoE expression was similar to controls. The increase in immunoreactive apoD in hippocampal extracts was more dramatic. At 1 DPL, immunoreactive apoD levels were already 16-fold higher than those in extracts of non-lesioned animals and, at 31 DPL, levels were still 8-fold higher than those of control animals. Finally, we have demonstrated that the levels of apoD in the brains of apoE-deficient mice are 50-fold those of wildtype control mice. ApoD clearly has an important function within the CNS in both normal and pathological situations.

Alterations in neuropeptide Y, tyrosine hydroxylase, and Y-receptor subtype distribution following spinal nerve injury to rats

Recent animal models of experimental nerve injury have proven useful in evaluating potential sympathetic involvement in neuropathic pain syndromes. We have employed a widely adopted unilateral L 5/L 6 spinal nerve ligation model to compare the development of mechanical allodynia with neurochemical changes both at the site of peripheral nerve injury and in the dorsal root ganglia (DRG). We have focused on the expression of neuropeptide Y (NPY), a well-studied regulatory peptide and phenotypic marker of sympathetic neurons, and functionally related Y-receptor binding sites following nerve injury. In sympathetic neurons, NPY is colocalized and coreleased with norepinephrine (NE) at peripheral sites of action. Furthermore, NPY gene expression is induced within the population of medium- and large-diameter DRG neurons of the A β-fiber class after experimental nerve injury. We therefore hypothesized that concurrent alterations in NPY and NE expression by sympathetic and sensory neurons may be a contributing factor to sympathetically-maintained neuropathic conditions. Animals with unilateral L 5/L 6 spinal nerve ligation developed mechanical allodynia of the hind paw ipsilateral to the site of injury that persisted until sacrifice at postoperative day 10. A significant induction of preproneuropeptide Y-encoding (PPNPY) mRNA, as detected by in situ hybridization histochemistry (ISHH), occurred in populations of medium- and large-diameter DRG neurons ipsilateral to the site of injury. Immunohistochemical analysis indicated a marked decline in the number of labeled sympathetic axons positive for tyrosine hydroxylase-like and NPY-like immunoreactivities (TH-Ll and NPY-LI, respectively) proximal to the site of nerve injury and almost complete elimination of immunopositive fibers distal to the site of ligation. Whereas, the extent of colocalization of NPY-LI to TH-LI-positive sympathetic axons in unaffected L 4 or L 5 nerve segments exceeded 80%, this figure declined to approximately 50% in regenerating axons of ligated spinal nerve L 5. The portion of NPY-LI that was not colocalized to sympathetic TH-LI-positive fibers was most likely contributed by regenerating sensory axons, consistent with marked de novo synthesis of NPY by DRG neurons. In end bulb axon terminals, i.e. morphological profiles characteristic of neuromas, NPY-LI-positive elements that were not colocalized to TH-LI-positive sympathetic elements appeared to be spatially segregated from those of sympathetic origin with colocalized TH-LI and NPY-LI. Receptor autoradiography indicated that small- and medium-diameter DRG somata of the C-fiber class normally express both Y 1 and Y 2 receptor subtypes. The pattern of the distribution of Y-receptor binding sites appeared to be relatively unaffected by spinal nerve ligation. In contrast, there was a marked increase in the density of Y 2 receptor binding sites in the proximal segment of ligated spinal nerve L 5, consistent with previously published data indicating differential transport of the Y 2 autoregulatory receptor subtype to nerve terminals. Induction of NPY gene expression in injured DRG neurons is consistent with appearance of NPY-LI-positive end bulbs derived from regenerating sensory axons that are found in developing neuromas containing a relatively high density of transported prejunctional Y 2 receptors. Newly established functional interactions of spatially segregated sensory- and sympathetically-derived end bulbs in developing neuromas may enhance neuronal hyperexcitability engendered by aberrant electrical activity at the site of injury. Injury-related alterations in the regulatory activities of NPY released within the DRG at somally-distributed Y-receptors may also contribute to the development and/or persistence of symptoms characteristic of sympathetically-maintained pain. Finally, at later times NPY-mediated modulation of NE release from invading sympathetic axon terminals within the DRG may affect the extent of α 2 receptor-mediated neuronal hyperexcitability associated with neuropathic pain.

A tetrodotoxin-resistant voltage-gated sodium channel from human dorsal root ganglia, hPN3/ SCN10A

Neuropathic pain may be produced, at least in part, by the increased activity of primary afferent neurons. Studies have suggested that an accumulation of voltage-gated sodium channels at the site of peripheral nerve injury is a primary precursory event for subsequent afferent hyperexcitability. In this study, a human sodium channel (hPN3, SCN10A) has been cloned from the lumbar 4/5 dorsal root ganglia (DRG). Expression of hPN3 in Xenopus oocytes showed that this clone is a functional voltage-gated sodium channel. The amino acid sequence of hPN3 is most closely related to the rat PN3/SNS sodium channels which are expressed primarily in the small neurons of rat DRGs. The homologous relationship between rPN3 and hPN3 is defined by (i) a high level of sequence identity (ii) sodium currents that are highly resistant to tetrodotoxin (TTX) (iii) similar tissue distribution profiles and (iv) orthologous chromosomal map positions. Since rPN3/SNS has been implicated in nociceptive transmission, hPN3 may prove to be a valuable target for therapeutic agents against neuropathic pain.

GP130 cytokines, leukemia inhibitory factor and interleukin-6, induce neuropeptide expression in intact adult rat sensory neurons in vivo: Time-course, specificity and comparison with sciatic nerve axotomy

The gp130 cytokines leukemia inhibitory factor and interleukin-6 are neuroactive cytokines associated with peripheral nerve injury. Here we show that exogenous administration of these factors selectively regulates neuropeptide phenotype in intact sensory neurons in a manner consistent with their role as injury-induced factors. Intraneural injection of leukemia inhibitory factor into the intact sciatic nerve of adult rats induces a significant increase in the percentage of neuronal profiles immunoreactive for galanin in the L4 and L5 dorsal root ganglia without altering the percentage profiles immunoreactive for vasoactive intestinal polypeptide or neuropeptide Y. Galanin-immunoreactivity was predominantly confined to those neurons which retrogradely transported and accumulated leukemia inhibitory factor. The up-regulation of galanin-immunoreactivity observed in L4 and L5 dorsal root ganglia following unilateral axotomy of the sciatic nerve was significantly reduced following continuous treatment for two weeks with a monoclonal antibody against the gp130 receptor motif. Intraneural injection of interleukin-6 into the intact sciatic nerve also significantly increased the percentage of neuronal profiles which displayed galanin-immunoreactivity but not vasoactive intestinal polypeptide or neuropeptide Y-immunoreactivity. Our results indicate that cytokines which interact with the gp130 receptor at the site of peripheral nerve injury contribute to the cell body response to axotomy. Changes in the levels of such cytokines however are insufficient to account for the complete repertoire of neuropeptide phenotypic changes associated with peripheral nerve injury.

SS-11-4 Effect of a prostacyclin derivative on cutaneous nerves in diabetic neuropathy

Chronic constriction injury (CCI) to peripheral nerve causes a painful neuropathy in association with a process of axonal degeneration and endoneural remodeling that involves macrophage recruitment and local increase in extracellular proteases and tumor necrosis factor alpha (TNF-α). Cell surface activation of TNF-α from its transmembrane precursor, as well as sequestration of TNF-α receptors II and I, is performed by the zinc-dependent endopeptidase family of matrix metalloproteinases (MMPs). Among TNF-α-converting MMPs, basal lamina degrading gelatinases are thought to play a role in sciatic nerve injury. In the present study, we determined the forms of TNF-α involved in the development of CCI neuropathy in rats, using Western blot analysis, and the temporal correlation of TNF-α and TNFRI protein profiles with gelatinases activity at the site of peripheral nerve injury. We observed two peaks in TNF-α protein during the first week of CCI that correspond to previously reported peaks in painful behavior. We propose that the first peak at 6 h post-CCI is due to the local expression of the cytotoxic transmembrane 26 kDa TNF-α protein released by resident Schwann cells, mast cells and macrophages. This peak in TNF-α protein expression corresponds to an increase in gelatinase B (MMP-9) activity, which is greatly upregulated as early as 3 h following CCI to rat sciatic nerve. The second peak occurs at 5 days post-CCI, and may represent TNF-α protein released by hematogenously recruited macrophages. This peak is marked by the increase in active soluble 17 kDa TNF-α and by gelatinase A (MMP-2) upregulation. These observations suggest that there is a pathogenic role for the TNF-α-converting function of MMP-2 in painful CCI neuropathy. We conclude that severe nerve injury induces MMPs, TNF-α and TNFRI, which interactively control the privileged endoneurial environment and the pathogenesis of the painful neuropathies associated with the macrophage-dependent processes of Wallerian degeneration.

Sciatic Cryoneurolysis in Rats

The purpose of this study was to investigate the possibility that sympathetic exacerbation of neuropathic pain activity may be mediated in part by the development of abnormal peripheral adrenergic mechanisms at the site of peripheral nerve injury. We evaluated changes in mechanical stimulation withdrawal thresholds before and after the delivery of selected alpha-adrenergic agonists and antagonists to the immediate area of a prior nerve injury in rats that had developed continuous mechanical allodynia subsequent to sciatic cryoneurolysis (SCN). Allodynia was attenuated (thresholds increased) after administration of the alpha 1 antagonist prazosin, but not the alpha 2 antagonist idazoxan. Similar attenuation occurred with infusions of the alpha 2 agonist dexmedetomidine and at the lowest dose (2.0 micrograms) of the mixed alpha agonist clonidine. In contrast, allodynia was exacerbated (thresholds decreased) by infusion of the highest dose of clonidine (20 micrograms). Infusions of the alpha 2 agonist ST-91, a polar analog of clonidine, did not alter withdrawal thresholds. The findings suggest that a minimal peripheral adrenergic modulation of SCN-induced allodynia occurs via mechanisms that are not localized to the prior injury site. However, overall, the SCN model of neuropathic pain appears to be resistant to adrenergic interventions, providing further evidence that SCN in rats is a model of sympathetically independent pain (SIP).

Apolipoprotein E: cholesterol transport protein with expanding role in cell biology.

Apolipoprotein E is a plasma protein that serves as a ligand for low density lipoprotein receptors and, through its interaction with these receptors, participates in the transport of cholesterol and other lipids among various cells of the body. A mutant form of apolipoprotein E that is defective in binding to low density lipoprotein receptors is associated with familial type III hyperlipoproteinemia, a genetic disorder characterized by elevated plasma cholesterol levels and accelerated coronary artery disease. Apolipoprotein E is synthesized in various organs, including liver, brain, spleen, and kidney, and is present in high concentrations in interstitial fluid, where it appears to participate in cholesterol redistribution from cells with excess cholesterol to those requiring cholesterol. Apolipo-protein E also appears to be involved in the repair response to tissue injury; for example, markedly increased amounts of apolipoprotein E are found at sites of peripheral nerve injury and regeneration. Other functions of apolipoprotein E, unrelated to lipid transport, are becoming known, including immunoregulation and modulation of cell growth and differentiation.