Autonomic fiber sprouting in the skin in chronic inflammation

Pain is a major symptom associated with chronic inflammation. In previous work from our laboratory, we have shown that in animal models of neuropathic pain there is a sprouting of sympathetic fibers into the upper dermis, a territory normally devoid of them. However, it is not known whether such sympathetic spouting, which is likely trophic factor mediated, also occurs in chronic inflammation and arthritis. In the present study, we used a rat model of chronic inflammation in which a small single dose of complete Freund's adjuvant (CFA) was injected subcutaneously, unilaterally, into the plantar surface of the hindpaw. This led to a localized long-term skin inflammation and arthritis in all joints of the hindpaw. Animals were perfused with histological fixatives at 1, 2, 3 or 4 weeks after the injection. Experimental animals treated with CFA were compared to saline-injected animals. We then investigated the changes in the pattern of peripheral innervation of the peptidergic nociceptors and sympathetic fibers in rat glabrous hindpaw skin. Antibodies directed towards calcitonin gene-related peptide (CGRP) and dopamine beta-hydroxylase (DBH) were used for the staining of peptidergic and sympathetic fibers, respectively. Immunofluorescence was then used to analyze the different nerve fiber populations of the upper dermis. At 4 weeks following CFA treatment, DBH-immunoreactive (IR) fibers were found to sprout into the upper dermis, in a pattern similar to the one we had observed in animals with a chronic constriction injury of the sciatic nerve in a previous publication. There was also a significant increase in the density of CGRP-IR fibers in the upper dermis in CFA treated animals at 2, 3 and 4 weeks post-injection. The increased peptidergic fiber innervation and the ectopic autonomic fibers found in the upper dermis may have a role in the pain-related behavior displayed by these animals

Changes in the spinal cord and peripheral innervation in an animal model of arthritis

Neurons in the marginal layer (lamina I) of the dorsal horn of the spinal cord play a major role in the transmission and integration of pain-related sensory information that is relayed to the brain. Alteration in excitability of these cells greatly influences pain perception. Among these, alterations of the substance P (SP) system play a major role because of its known involvement in spinal cord nociceptive mechanisms. In this thesis, our main focus was on the characterization of the cell populations in lamina I of the spinal cord which express the SP receptor (NK-1r) and project to the parabrachial nucleus in normal rats and in an animal model of localized polyarthritis. Lamina I projection neurons can be classified into three morphological types, the fusiform, the multipolar (flattened) and the pyramidal. Our combined tract-tracing and immunocytochemical studies demonstrated that in control animals the fusiform and multipolar neurons project abundantly to the parabrachial nuclei and express the NK-1r, whereas pyramidal neurons, although projecting in almost identical proportion to the same target, express little, if any, NK-1r. In rats treated with a single, unilateral low dose subcutaneous injection of complete Freund's adjuvant (CFA) in the thick skin of the hind paw, we demonstrated an ipsilateral de novo NK-1r expression on the normally non-nociceptive spinoparabrachial lamina I pyramidal cell type starting at 15 days post-injection. We also observed, as from 15 days post-CFA, an innervation of pyramidal neurons by SP-immunoreactive (IR) boutons. It should be pointed out that pyramidal neurons are normally not innervated by SP, which would confirm their non-nocicDans la moelle épinière, les neurones de la couche marginale (couche 1) de la corne dorsale jouent un rôle majeur dans l'intégration et la transmission de l'information sensorielle vers le cerveau. Des changements au niveau de l'excitabilité de ces cellules influencent grandement la perception de la douleur. Parmi ceux-ci, un changement au niveau du système de la substance P (SP) peut avoir un grand impact en raison de son implication dans les mécanismes nociceptifs. Dans cette thèse, notre but premier était de caractériser la population neuronale de la couche 1 qui exprime le récepteur de la substance P (NK-1 et qui projette au noyau parabrachial. Les observations se sont faites chez les rats normaux et dans un modèle animal de polyarthrite locale. Les cellules de projection de la couche 1 peuvent être classifiées en trois types morphologiques; les fusiformes, les multipolaires (aplaties) et les pyramidales. Notre approche combinant le traçage rétrograde et l'immunocytochimie a démontré que, chez les animaux contrôles, les neurones fusiformes, multipolaires et pyramidaux projettent abondamment au noyau parabrachial. Les deux premiers types de cellules expriment le récepteur NK-1, alors que les cellules pyramidales l'expriment très peu, sinon pas. Chez les rats traités avec une seule dose unilatérale d'adjuvant complet de Freund (ACF), administrée sous-cutanée dans la plante de la patte, nous avons démontré une nouvelle expression du récepteur NK-1. Les cellules pyramidales qui sont habituellement non nociceptives sont imunoréactives pour le récepteur NK-1 à partir de 15 jours après l'injection. Nous avons aussi observé, à 15 jours ap