Inhibition of ACTH release by a central inhibitory mechanism in the basal forebrain

Abstract

Experiments were designed to study the actions of a known central inhibitory region in the basal forebrain on ACTH release. The region of the diagonal band (Broca) and the rostral basal preoptic region was stimulated in encéphale isolé cats at parameters which produced central inhibition as indicated by electrocortical synchronization while simultaneously collecting 5-min sequential samples of adrenal venous blood for determination of cortisol content. Stimulation of the basal forebrain inhibitory region resulted in a delayed and prolonged inhibition of the tonic or ongoing level of activity in the pituitary-adrenal axis. To test the inhibitory action of this region on facilitation of ACTH release by stressful stimuli, a brief stimulus was applied to the reticular activating system during basal forebrain stimulation. A prompt increase in steroid output occurred. Thus, the central inhibitory mechanism in the basal forebrain inhibits the tonic activity of the pituitary-adrenal axis but not its phasic responses to stressful stimuli. This action on hypothalamohypophyseal activity is part of the general central suppressor function of the basal forebrain inhibitory region.