LONG-TERM EFFECTS OF NEONATAL CAPSAICIN ON C-FIBER EXCITABILITY AND DORSAL HORN C-INPUT PROCESSING IN THE RAT

The effects of neonatal capsaicin treatment (50 mg/kg, SC, at day 2 of postnatal life) on C-fiber excitability and dorsal horn C-input proce ssing were studied through recording of a C-fiber-evoked spinal flexor reflex in 55-60-day-old rats, anesthetized with urethane (1.1 g/kg, I P) and spinalized at Th9-10. Neonatal capsaicin resulted in decreased C-fiber excitability, as revealed by increased chronaxie values determ ined in a strength-duration paradigm. Besides, capsaicin-treated rats exhibited a reduced potentiation of the C-reflex discharge in response to repetitive stimulation. The results indicate that capsaicin given to rats early in life leads to both functional disturbances of survivi ng C-fibers and altered temporal synaptic processing of the C-input in the spinal cord.