The influence of capsaicin sensitive neurons on stress-induced release of ACTH.

Changes in the plasma levels of ACTH in response to cold exposure or restraint stress were measured in adult rats which had been pretreated with capsaicin or vehicle as neonates. There was no difference in basal ACTH levels between capsaicin and vehicle pretreated animals. Following restraint stress, ACTH levels rose similarly in vehicle and capsaicin pretreated rats, indicating that the pituitary-adrenal system is not impaired by capsaicin pretreatment. However, following cold exposure ACTH levels rose only in control animals whereas no change was observed in capsaicin pretreated animals. It is concluded that capsaicin-sensitive afferent neurons participate in the cold stress-induced increase of plasma ACTH levels.