INHIBITION OF PITUITARY-ADRENAL ACTIVITY AS A CONSEQUENCE OF CONSUMMATORY BEHAVIOR

(1) We have demonstrated that if food and water are restricted to the morning hours, the circadian rhythms of the pituitary-adrenal system are re-entrained and the levels of plasma corticosteroids are elevated in the morning, whereas they are usually low during that period in the rodent. Following drinking, however, there is, within 5 min, a sharp decline in plasma corticoids accompanied by an equivalent drop in ACTH. Thus, in addition to the regulation of ACTH by the usual feedback of circulating corticosteroids, there appears to be an independent central nervous system inhibitory mechanism which can cause ACTH and corticosteroids to drop concomitantly. (2) We demonstrated that the availability of a consummatory response can reduce an organism's pituitary-adrenal response to a normally stressful situation. (a) When exposed to novelty, animals usually show a striking elevation of plasma corticosterone. However, if a consummatory response-drinking-is available in the novel environment, the response to this novel environment is markedly reduced. (b) The availability of an adjunct behavior-drinking-in a situation where animals are placed on an intermittent food reinforcement schedule also causes a significant reduction in plasma corticosterone levels. (c) Shock-induced fighting results in a reduced ACTH response to shock. Fighting behavior can also be viewed as a consummatory response. (3) We believe these experiments demonstrate the bidirectionality of the pituitary-adrenal system. Since the pituitary-adrenal system appears to provide a sensitive measure of arousal state, and since consummatory responses suppress the activity of this system, it therefore appears that consummatory behavior has arousal-reducing properties. © 1979.