Inhibitory and facilitatory areas of the rostral pons mediating ACTH release in the cat.

To define the role of the rostral pons in the control of release of ACTH, we stimulated electrically (30 sec, 200 muA, 50 Hz) 128 sites in the dorsal rostral pons of 20 cats anesthetized with chloralose/urethane. Responses of arterial pressure to electrical stimulation were prevented by lesions placed previously in the medulla. Plasma concentrations of ACTH were measured by radioimmunoassay. Active areas consisted of three regions: 1) lateral inhibitory: Locus subcoeruleus and anteroventral locus coeruleus (mean deltaACTH: -189, -164, -145 pg/ml at 1.5,3.0 and 6.0 min respectively, P less than 0.01);2) intermediate facilitatory:principal locus coeruleus and lateral ventral tegmental nucleus (mean deltaACTH: +81, +68, +37 pg/ml; P less than 0.05); and 3) medial inhibitory: dorsal tegmental nucleus, dorsal raphé and medial ventral tegmental nucleus (mean deltaACTH; -211, -212, -115 pg/ml; P less than 0.01). The former two areas received direct projections from medullary neurons activated or inhibited by atrial stretch, and, in turn, give rise to adrenergic and cholinergic projections to the medial hypothalamus. Since the release of ACTH is inversely correlated with right atrial stretch, the results suggest that the lateral inhibitory area and the intermediate facilitatory area are involved in mediation of changes in release of ACTH in response to hemodynamic changes.