CORTICOSTERONE IMPLANTS IN THE PARAVENTRICULAR NUCLEUS INHIBIT ACTH AND CORTICOSTERONE RESPONSES AND THE RELEASE OF CORTICOTROPIN-RELEASING FACTOR FOLLOWING NEURAL STIMULI

Experiments were conducted on the possible role of corticosterone (CS), at the level of the paraventricular nucleus of the hypothalamus (PVN) and dorsal hippocampus (D.HIPP), in the negative feedback effects following neural stimuli. In rats with bilateral PVN cholesterol (CHO) implants, acoustic and photic stimuli caused a significant rise in serum CS and ACTH and depletion of median eminence (ME) CRF-41 content. CS PVN implants have prevented the rise in serum CS, ACTH and ME CRF-41 depletion. Bilateral CHO or CS implants in the D.HIPP did not modify the responses of the hypothalamo-pituitary-adrenal axis to the above neural stimuli. In PVN CS-implanted rats, i.v. injection of CRF-41 increased serum CS similar to that observed in PVN CHO-implanted animals. These data are discussed in view of previous experiments on corticosteroid implants in the brain. It is concluded that CS PVN implants, by acting possibly via type II hypothalamic receptors, have prevented the release of ME CRF-41 following neural stimuli and consequently the secretion of ACTH and CS.