Previous findings suggested that the medial basal hypothalamus (MBH) represents the hypophysiotrophic area. In the present studies the neural connections of the MBH were partially or totally interrupted, and the functional capacity of this neurally isolated region to regulate pituitary-adrenal activity was investigated. One and four weeks after the interruption of all neural afferents to the MBH, corticocosterone levels were found to be very high in peripheral plasma and in the adrenal gland compared to sham operated controls. Corticosteroid titers in the adrenal venous effluent, however, were essentially equivalent in experimental and control rats. Surgical stress (ether anesthesia and unilateral adrenalectomy) has further increased corticosterone levels in these rats, and adrenal compensatory hypertrophy developed following removal of one adrenal. The diurnal rhythm in ACTH secretion, demonstrable in normal animals, was not evident after complete dcaffcrcntation of the MBH. The interruption of lateral, dorsal, and posterior connections of the MBH did not interfere with the circadian ACTH rhythm. In contrast, transection of only the anterior pathways (frontal cut) disrupted the normal rhythm. These anterior pathways may convey afferent input of critical importance for the diurnal rhythm. It is concluded that ACTH secretion of the anterior pituitary is maintained by the MBH in the absence of neural input. For normal ACTH function, however, afferent impulses to the MBH are required.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience