Transient loss of terminals from non-peptidergic nociceptive fibers in the substantia gelatinosa of spinal cord following chronic constriction injury of the sciatic nerve

doi:10.1016/j.neuroscience.2005.11.051

Neuroscience

Volume 138, Issue 2, 2006, Pages 675-690

https://doi.org/10.1016/j.neuroscience.2005.11.051 Get rights and content

Abstract

It is well known that following peripheral nerve injury, there are numerous changes in neurotransmitter and neuropeptide expression in the superficial dorsal horn, the dorsal root ganglion and the periphery. Of particular interest are the relative contributions of two sub-types of unmyelinated C-fibers in the initiation and maintenance of chronic pain, the peptidergic, and the non-peptidergic. Evidence gathered in recent years has led researchers to believe that the non-peptidergic nociceptive primary afferents are functionally distinct from their peptidergic counterpart. For our study, we used a well-established animal model of constriction neuropathy (the Kruger model) and studied Wistar rats at 5, 7, 10, 15 and 21 days after nerve lesion caused by the application of a fixed-diameter polyethylene cuff to the left sciatic nerve. Animals were assessed for the onset and evolution of mechanical allodynia using calibrated von Frey filaments and were additionally tested for thermal (heat and cold) hypersensitivity. Immunocytochemical detection of calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4) binding was used to visualize the dorsal horn distribution of the boutons from the peptidergic and non-peptidergic fibers respectively. Using confocal microscopy and image analysis, we detected a significant decrease in the density of IB4-labeled boutons, ipsilateral to the lesion, at seven and 10 days following nerve injury. The density of IB4-labeled varicosities retuned to control levels by 15 days. There were no significant changes in the density of CGRP-labeled varicosities at all time points examined. Applying electron microscopy, we initially detected degenerative changes in the central elements of type I glomeruli and then a considerable reduction in their number followed by recovery at 15 days post-lesion. As the central boutons of type Ia represent varicosities from the fibers which bind IB4, the ultrastructural changes confirmed that there was a bona fide transient loss of varicosities, not simply a loss of IB4 binding. These data indicate that, in this animal model, morphological changes in the nociceptive C-fiber input of the rat dorsal horn are restricted to the non-peptidergic sub-population and are transient in nature. Furthermore, such changes do not correlate with the time-course of the allodynia.

Section snippets

Experimental procedures

The guidelines contained in the Guide to the Care and Use of Experimental Animals of the Canadian Council on Animal Care, Volumes 1 and 2, were rigorously followed. Furthermore, all protocols were reviewed and approved by the McGill University Animal Care Committee before experimentation began. All measures were taken to minimize the number of animals used and their suffering.

Analysis of behavioral changes in sham-operated and neuropathic animals

Qualitative assessment of animal behavior following cuff application revealed that animals in the neuropathic group exhibited signs of nociceptive behavior including limping and guarding of the left (ipsilateral) hind paw. Guarding consisted of maintained withdrawal of the paw in an everted position with the toes together and slightly ventroflexed. Neuropathic animals exhibited signs of increased mechanical sensitivity at the 4g threshold by the 7th day following cuff application. This reached

Discussion

In this study, we confirmed that, following a chronic constriction injury of the sciatic nerve (CCI), there is a transient loss of IB4 binding in the dorsal horn of the spinal cord ipsilateral to the lesion. Furthermore, by expanding our study to the ultrastructural level, we were able to demonstrate that there was a bona fide loss of varicosities from non-peptidergic unmyelinated fibers, not simply a loss of binding sites, followed by an apparent restoration of the synaptic structure.

Conclusions

In this study, using a well-established neuropathic pain animal model, we detected for the first time a transient but selective loss of boutons from non-peptidergic nociceptive afferents which represent the central terminals of type I glomeruli in the spinal cord of these animals. The significance of these changes for the evolution of the pain is at present unclear, although they may play a role in the initial stages of the development of the hyperalgesia and allodynia.

It is also evident that

Acknowledgments

This research was support by CIHR grant #38093 to A. Ribeiro-da-Silva. Andrea Bailey acknowledges a studentship from the Louise Edwards Foundation. We are grateful to Gary J. Bennett and Véronique Kéna-Cohen for their help with the animal behavior, to Sid Parkinson for editorial assistance, and to Manon St. Louis, Vanessa Partridge and Johanne Ouellette for technical expertise.

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Systems neuroscienceTransient loss of terminals from non-peptidergic nociceptive fibers in the substantia gelatinosa of spinal cord following chronic constriction injury of the sciatic nerve

Abstract

Section snippets

Experimental procedures

Analysis of behavioral changes in sham-operated and neuropathic animals

Discussion

Conclusions

Acknowledgments

Exp Neurol

Prog Brain Res

Pain

Pain

Neurosci Biobehav Rev

Pain

Pharmacol Biochem Behav

Pain

Brain Res

Pain

Neuroscience

Neurosci Lett

Brain Res

Dev Brain Res

Mol Brain Res

J Pain

Exp Neurol

Neuroscience

Neurosci Lett

Nociceptors for the 21st century

Curr Rev Pain

Functional downregulation of P2X3 receptor subunit in rat sensory neurons reveals a significant role in chronic neuropathic and inflammatory pain

J Neurosci

Postnatal changes in the expression of the trkA high-affinity NGF receptor in primary sensory neurons

Eur J Neurosci

GAP-43 distribution is correlated with development of growth cones and presynaptic terminals

J Neurocytol

Time course of degenerative and regenerative changes in the dorsal horn in a rat model of peripheral neuropathy

J Comp Neurol

Systems neuroscience
Transient loss of terminals from non-peptidergic nociceptive fibers in the substantia gelatinosa of spinal cord following chronic constriction injury of the sciatic nerve