vasoactive-intestinal-peptide and Peripheral-Nerve-Injuries

Neuropathic pain arising from direct trauma to, or compression injury of, peripheral nerves is a common clinical problem. It is characterized by the development of abnormal pain states (spontaneous pain, hyperalgesia, allodynia), which can persist long after the initial injury has resolved. The underlying mechanisms are poorly understood and, as a consequence, treatment is often unsatisfactory. Some of the main contributing factors are thought to be the morphological and phenotypic changes that occur centrally, including alterations in the expression of neurotransmitters and their associated receptors, both in the dorsal root ganglia and in the spinal dorsal horn. This article focuses on the functional role of the two structurally related peptides VIP and PACAP within the spinal cord, and their possible contribution to the altered transmission of sensory information in neuropathic conditions.

Topics: Animals; Ganglia, Spinal; Neuropeptides; Pain; Peripheral Nerve Injuries; Peripheral Nerves; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Pituitary Hormone; Receptors, Vasoactive Intestinal Peptide; Receptors, Vasoactive Intestinal Peptide, Type II; Receptors, Vasoactive Intestinal Polypeptide, Type I; Second Messenger Systems; Spinal Cord; Vasoactive Intestinal Peptide

Nerve injuries often result in neuropathic pain with co-morbid changes in social behaviours, motivation, sleep-wake cycles and neuroendocrine function. In an animal model of neuropathic injury (CCI) similar co-morbid changes are evoked in a subpopulation (~30%) of injured rats. In addition to anatomical evidence of altered neuronal and glial function, the periaqueductal grey (PAG) of these rats shows evidence of cell death. These changes in the PAG may play a role in the disruption of the normal emotional coping responses triggered by nerve injury. Cell death can occur via a number of mechanisms, including the disruption of neuroprotective mechanisms. Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two endogenous neuropeptides whose activities are tightly regulated by two receptors subtypes, namely the PAC1 and VPAC receptors. These peptides and their receptors exert robust neuroprotective roles. In these studies, we hypothesized that rats expressing disabilities following CCI showed altered expression of PACAP and VIP in the PAG. Rats were categorized as having either Pain alone, Transient or Persistent disability, based on changes in social behaviours pre- and post-CCI. Social interaction behavioural tested (BT), sham-injured and naïve untested rats were also included. For measurements of mRNA and protein expression we utilised micro-dissected PAGs blocks taken from each group. At the mRNA level, VIP was downregulated and PAC1 was upregulated in BT animals, whilst VPAC1 mRNA was specifically increased in the Pain alone group. Interestingly, protein levels of both PACAP and VIP were remarkably increased in the Persistent Disability group. Taken together, sciatic nerve CCI that triggers neuropathic pain and persistent disability results in abnormally increased VIP and PACAP expression in the PAG. Our data also suggest that these effects are likely to be governed by post-transcriptional mechanisms.

Topics: Animals; Behavior, Animal; Male; Neuralgia; Pain Measurement; Periaqueductal Gray; Peripheral Nerve Injuries; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats, Sprague-Dawley; Sciatic Nerve; Social Behavior; Vasoactive Intestinal Peptide

Vasoactive intestinal peptide (VIP) is one of the neuropeptides showing the strongest up-regulation in the nociceptive pathway after peripheral nerve injury and has been proposed to support neuropathic pain. Nevertheless, the story may be more complicated considering the known suppressive effects of the peptide on the immune reactivity of microglial cells, which have been heavily implicated in the onset and maintenance of pain after nerve injury. We here used mice deficient in VIP and the model of spared nerve injury, characterized by persistent tactile hypersensitivity. While tactile hypersensitivity developed similarly to wild type mice for the ipsilateral hindpaw, only transgenic mice showed a mirror-image tactile hypersensitivity in the contralateral hindpaw. This exacerbated neuropathic pain phenotype appeared to be mediated through a local mechanism acting at the level of the lumbar spinal cord as a distant nerve lesion in the front limb did not lead to hindpaw hypersensitivity in VIP-deficient mice. Innocuous tactile hindpaw stimulation was found to increase a neuronal activation marker in the bilateral superficial laminae of the lumbar dorsal horn of VIP-deficient, but not wild type mice, after SNI. A deeper study into the immune responsiveness to the nerve lesion also proved that VIP-deficient mice had a stronger early pro-inflammatory cytokine response and a more pronounced microglial reactivity compared to wild type controls. The latter was also observed at four weeks after spared nerve injury, a time at which bilateral tactile hypersensitivity persisted in VIP-deficient mice. These data suggest an action of VIP in neuropathic states that is more complicated than previously assumed. Future research is now needed for a deeper understanding of the relative contribution of receptors and fiber populations involved in the VIP-neuropathic pain link.

Topics: Animals; Calcium-Binding Proteins; Cytokines; Disease Models, Animal; Female; Functional Laterality; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microfilament Proteins; Neuralgia; Neurogenic Inflammation; Pain Measurement; Peripheral Nerve Injuries; Proto-Oncogene Proteins c-fos; Time Factors; Vasoactive Intestinal Peptide

In order to investigate whether cholera toxin B subunit (CTb) is transported by unmyelinated primary afferents following nerve injury, we transected the sciatic nerves of six rats, and injected the transected nerves (and in three cases also the intact contralateral nerves) with CTb, 2 weeks later. The relationship between CTb and two neuropeptides, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), was then examined in neurons in the ipsilateral L4 and L5 dorsal root ganglia, using immunofluorescence staining and confocal microscopy. We also immunostained sections of spinal cord and caudal medulla for CTb, NPY and VIP. Following nerve section, VIP immunoreactivity was increased in laminae I-II of the spinal cord while NPY immunoreactivity was increased in laminae III-IV of the spinal cord and in the gracile nucleus. On the contralateral side, CTb labelling was detected in laminae I and III-V of the dorsal horn of the L4 and L5 spinal segments, as well as in the gracile nucleus. CTb labelling was seen in the same areas on the lesioned side, but with a dramatic increase in lamina II. No VIP or NPY immunoreactivity was observed in L4 and L5 dorsal root ganglia on the side of the intact nerve, but on the lesioned side VIP was detected in many small neurons and NPY in numerous large neurons. In agreement with the report by Tong et al. [J. Comp. Neurol. 404 (1999) 143], we found that while CTb labelling in the dorsal root ganglion on the side of the intact nerve was mainly in large neurons, on the lesioned side CTb was present in dorsal root ganglion neurons of all sizes. The main finding of the present study was that almost all of the VIP- (96%) and NPY- (98%) positive neurons in the dorsal root ganglia on the lesioned side were also CTb-labelled. After nerve injury VIP is upregulated in fine afferents that terminate in laminae I and II, and most of these probably have unmyelinated axons. Since the cell bodies of these neurons were labelled with CTb that had been injected into the transected sciatic nerve, this suggests that many of these fine afferents, which do not normally transport CTb, are capable of doing so after injury.

Topics: Afferent Pathways; Animals; Cholera Toxin; Fluorescent Antibody Technique; Ganglia, Spinal; Immunoenzyme Techniques; Medulla Oblongata; Microscopy, Confocal; Nerve Fibers, Unmyelinated; Neuropeptide Y; Peripheral Nerve Injuries; Peripheral Nerves; Rats; Rats, Wistar; Sciatic Nerve; Spinal Cord; Vasoactive Intestinal Peptide

Peripheral nerve transection induces significant changes in neuropeptide expression and content in injured primary sensory neurons, possibly due to loss of target derived neurotrophic support. This study shows that neurotrophin-3 (NT-3) delivery to the injured nerve influences neuropeptide Y (NPY) expression within dorsal root ganglia (DRG) neurons. NT-3 was delivered by grafting impregnated fibronectin (500 ng/ml; NT group) in the axotomised sciatic nerve. Animals grafted with plain fibronectin mats (FN) or nerve grafts (NG) were used as controls. L4 and L5 DRG from operated and contralateral sides were harvested between 5 and 240 d. Using immunohistochemistry and computerised image analysis the percentage, diameter and optical density of neurons expressing calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP) and NPY were quantified. Sciatic nerve axotomy resulted in significant reduction in expression of CGRP and SP, and significant upregulation of VIP and NPY (P < 0.05 for ipsilateral vs contralateral DRG). By d 30, exogenous NT-3 and nerve graft attenuated the upregulation of NPY (P < 0.05 for NT and NG vs FN). However, NT-3 administration did not influence the expression of CGRP, SP or VIP. The mean cell diameter of NPY immunoreactive neurons was significantly smaller in the NT-3 group (P < 0.05 for NT vs FN and NG) suggesting a differential influence of NT-3 on larger neurons. The optical densities of NPY immunoreactive neurons of equal size were the same in each group at any time point, indicating that the neurons responding to NT-3 downregulate NPY expression to levels not detectable by immunohistochemistry. These results demonstrate that targeted administration of NT-3 regulates the phenotype of a NPY-immunoreactive neuronal subpopulation in the dorsal root ganglia, a further evidence of the trophic role of neurotrophins on primary sensory neurons.

Topics: Analysis of Variance; Animals; Calcitonin Gene-Related Peptide; Fibronectins; Ganglia, Spinal; Image Processing, Computer-Assisted; Immunohistochemistry; Male; Nerve Growth Factors; Nerve Regeneration; Neurons, Afferent; Neuropeptide Y; Neurotrophin 3; Peripheral Nerve Injuries; Peripheral Nerves; Rats; Rats, Inbred Lew; Substance P; Time Factors; Vasoactive Intestinal Peptide

By in situ hybridization and immunohistochemistry, we examined the expression of neuropeptides such as neuropeptide Y (NPY), galanin (Gal), substance P (SP), vasoactive intestinal polypeptide (VIP) and their mRNAs in the rat mesencephalic trigeminal nucleus (Mes5) following masseteric nerve transection. On the side contralateral to the nerve transection, none of the peptides examined were labeled in Mes5 cell bodies. However, on the side ipsilateral to the lesion, NPY, Gal and preprotachykinin (PPT) mRNAs appeared in Mes5 cell bodies. Double labeling for mRNAs by in situ hybridization and retrograde tracer fluoro-gold (FG) revealed that almost all (96-97%) the FG-labeled neurons which were cut expressed NPY and Gal mRNAs, whereas less neurons (87%) expressed PPT mRNA. NPY and Gal-like immunoreactivities were detected in Mes5 cell bodies ipsilateral to the axotomy. The results suggested that these neuropeptides play roles in adaptive processes after peripheral nerve injury in Mes5 neurons as they are thought to do so in dorsal root ganglion neurons.

Topics: Animals; Galanin; In Situ Hybridization; Male; Masseter Muscle; Mesencephalon; Neuropeptide Y; Neuropeptides; Peptide Biosynthesis; Peptides; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; RNA, Messenger; Substance P; Trigeminal Nerve; Vasoactive Intestinal Peptide

The temporal course of changes in peptide expression in the dorsal root ganglia L4 and L5 and in the dorsal horn of the spinal cord has been studied in rats subjected to a sciatic nerve transection at a mid-thigh level following different survival times. Galanin-, substance P-, vasoactive intestinal polypeptide-, peptide histidine-isoleucine- and calcitonin gene-related peptide-like immunoreactivities have been studied both by immunohistochemistry and radioimmunoassay. Galanin messenger ribonucleic acid has also been studied by in situ hybridization in the dorsal root ganglia of normal and lesioned animals. In addition, a group of animals with a sciatic nerve crush was studied to compare possible differences in peptide expression after both types of lesions. The results show that the transection induces an increase in the number of cell bodies expressing galanin-like immunoreactivity in the ganglia, and that the galanin levels rise about 120-fold after three and 14 days of survival. This increase reflected increased synthesis of the peptide, since there was a rise in the galanin messenger ribonucleic acid already at 24 h post-lesion, which was maintained for at least 60 days. In the spinal cord there was an increase of staining in the midportion of the outer layers of the dorsal horn that corresponded to fibers thought to arise from cells of the dorsal root ganglia affected by the transection. Also a depletion of substance P-like and an increase in vasoactive intestinal polypeptide- and peptide histidine-isoleucine-like immunoreactivities in the dorsal root ganglia were confirmed. These changes were shown to be rapidly detectable and were paralleled by similar changes in the dorsal horn of the spinal cord. For calcitonin gene-related peptide the immunohistochemistry was inconclusive, and the radioimmunoassay showed no detectable changes. After nerve crush a transient increase in the number of galanin immunoreactive neurons was observed, as well as a decrease in the number of neurons showing substance P-like immunoreactivity. These changes were most noticeable between six and 14 days of survival. After this, peptide expression seemed to return slowly to normal, that is by day 45 post-crush only a few cells showed galanin-like, and many sensory neurons expressed substance P-like immunoreactivity. The results demonstrate that when primary sensory neurons are peripherally lesioned they respond in a complex manner, altering their normal production of peptides

Topics: Animals; Galanin; Ganglia, Spinal; Male; Nerve Crush; Neuropeptides; Peptides; Peripheral Nerve Injuries; Rats; Rats, Inbred Strains; Sciatic Nerve; Spinal Cord; Substance P; Vasoactive Intestinal Peptide