Intracerebroventricular ACTH activates the pituitary-adrenal system: dissociation from a behavioral response

In the rat, intracerebroventricular [i.c.v.] injection of synthetic ACTH (ACTH1-24, ACTH1-16) elevated plasma corticosterone levels and induced the display of excessive grooming behavior. The grooming response could be elicited in hypophysectomized rats without concomittant elevation of plasma corticosterone. In intact rats s.c. injection of ACTH1-24 and not of ACTH1-16-NH2 stimulated the release of adrenal corticosteroids, whereas no excessive grooming was observed. In contrast to the reduced effectiveness of a 2nd i.c.v. injection of ACTH in inducing the behavioral response, no single-dose tolerance was observed for the effect of i.c.v. ACTH on the pituitary-adrenal system. Two different central mechanisms underly the observed responses to the i.c.v. applied ACTH.