Neonatal capsaicin does not affect unmyelinated efferent fibers of the autonomic nervous system: functional evidence.

Visceral nociceptive thresholds, viscero-visceral reflexes and the effects of efferent stimulation of autonomic nerves has been studied in adult rats treated at birth with capsaicin. These animals showed visceral analgesia and depressed visceral reflexes. However, stimulation of unmyelinated efferent fibers in autonomic nerves produced normal effects. It is concluded that neonatal treatment with capsaicin destroys selectively unmyelinated afferent fibers.