Participation of the hypothalamus in the feedback regulation of the pituitary-adrenocortical system.

The activity of the pituitary-adrenocortical system, which was judged according to the level of corticosteroids in the blood, and the electrical response of the anterior, medial, and lateral hypothalamus to intravenous injection of hydrocortisone (1 mg/kg) were investigated in chronic experiments on rabbits with implanted semimicroelectrodes. It was shown that hydrocortisone induces an inhibition of the pituitary-adrenocortical function and changes the multineuronal activity of the hypothalamus. In the anterior hypothalamus, pools of neurons predominated, the discharge frequency of which was increased, while in the medial and lateral hypothalamus it was decreased. It is concluded that the corticosteroid feedback mechanisms are correlated with excitation of the anterior hypothalamus and inhibition of the medial hypothalamus. The key words are: hypothalamus, multineuronal activity corticorsteroids, and feedback.