Modification of serotonergic innervation of the rat spinal cord dorsal horn after neonatal capsaicin treatment.

Newborn rats were treated with Capsaicin. Seven weeks later, calcitonin gene-related peptide, substance P, and serotonin were detected immunocytochemically in the dorsal horn of the spinal cord. Peptide immunostaining, presumably located in primary afferents, was reduced in intensity, whereas the pattern of serotonin innervation was modified, suggesting a secondary reorganization due to the lesion of afferents. The possible mechanisms of this reorganization are discussed.