Neonatal capsaicin and thermal nociception: a paradox.

Thermal and mechanical nociceptive thresholds and somato-visceral reflexes have been studied in normal rats and in rats treated neonatally with capsaicin. Mechanical nociceptive thresholds were increased in capsaicin treated rats whereas thermal nociceptive thresholds remained unchanged. In contrast, somato-visceral reflexes evoked by thermal noxious stimulation of the skin could not be elicited in capsaicin treated rats whereas mechanical noxious stimulation was effective in evoking visceral reflexes.