Modifications of serotonin-, substance P- and calcitonin gene-related peptide-like immunoreactivities in the dorsal horn of the spinal cord of arthritic rats: a quantitative immunocytochemical study.

Adjuvant-induced arthritis has been produced in adult rats in order to study the reorganization of serotonergic innervation in the spinal cord dorsal horn in a model of chronic pain. Immunocytochemical detection of CGRP and substance P was quantified with an image analyzer, and we found a transient increase for both peptides at 1 and 2 months, followed by a decrease to control levels after four months. At variance, quantification of serotonergic immunoreactivity showed a significant increase which persisted throughout the study. The significance of this finding is discussed with comparison of other experimental models involving reorganization of primary afferents to the spinal cord.