The importance of the hypothalamic lateral retrochiasmatic area in the control of adrenocorticotropin and thyrotropin secretion.

Anterolateral hypothalamic deafferentiation was made in rats to explore the importance of the neural pathways through the lateral retrochiasmatic area (RCAL) in the regulation of ACTH and TSH secretion. In rats with complete bilateral RCAL transection, pituitary-adrenal function was altered in the following respects compared to sham-operated controls. 1) Basal plasma ACTH, corticosterone (B), and adrenal weight were depressed. 2) Plasma ACTH and B elevation in response to 3-min ether inhalation were markedly decreased or abolished. 3) Insulin-induced hypoglycemia produced no or little plasma B elevation. 4) Lysine-vasopressin was significantly less effective in inducing pituitary-adrenal activation. Reductions in plasma ACTH and B concentrations and adrenal weight were correlated with the completeness of the RCAL transection. The plasma TSH concentration was lower in the deafferented rats than in the controls regardless of the completeness of the cut at the RCAL, indicating that the neural pathways traversing this area do not possess a critical importance for the regulation of TSH if the rest of the hypothalamus is deafferented anterolaterally. We conclude that intact neural connections between the medial basal hypothalamus and the central nervous system at the RCAL are essential for the maintenance of normal hypothalamic-pituitary-adrenal function.