Inhibitory and Facilitatory Areas of the Rostral Pons Mediating ACTH Release in the Cat

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Abstract
To define the role of the rostral pons in the control of release of ACTH, 128 sites in the dorsal rostral pons of 20 cats anesthetized with chloralose/urethane were stimulated electrically (30 s, 200 .mu.A, 50 Hz). 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 3 regions: lateral inhibitory [locus subcoeruleus and anteroventral locus coeruleus (mean .DELTA.ACTH = -189, -164, -145 pg/ml at 1.5, 3.0 and 6.0 min respectively, P < 0.01)], intermediate facilitatory [principal locus coeruleus and lateral ventral tegmental nucleus (mean .DELTA.ACTH = +81, +68, +37 pg/ml; P < 0.05)], and medial inhibitory [dorsal tegmental nucleus, dorsal raphe and medial ventral tegmental nucleus (mean .DELTA.ACTH = -211, -212, -115 pg/ml; P < 0.01)]. The former 2 areas receive direct projections from medullary neurons activated or inhibited by atrial stretch, and 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.