Neonatal capsaicin treatment (NCT) alters the metabolic activity of the rat somatosensory cortex in response to mechanical deflection of the mystacial vibrissae.

Capsaicin, a selective neurotoxin of unmyelinated C-fibers, was administered to neonatal rat pups at birth. Following a recovery period of 10 days, pups were injected with 2-deoxy-glucose (2DG) and subjected to repetitive mechanical stimulation to the left whiskerpad. Their brains were then harvested for autoradiography. The observed changes in 2DG uptake in the somatosensory cortex of capsaicin-treated rats were compared to vehicle-treated rats. The cross-sectional area and density of 2DG uptake by the primary and the secondary somatosensory cortex (SSI and SSII, respectively) were measured. Capsaicin-treated rats significantly exhibited a reduction in area of activation and a decrease of 2DG uptake in both structures. The present data indicates that neonatal capsaicin affects the functional activity of the rat somatosensory cortex. It is suggested that unmyelinated sensory afferents play a role in the development of the rat somatosensory system.