PARAVENTRICULAR AND SUPRAOPTIC NUCLEI OF THE HYPOTHALAMUS ARE NOT EQUALLY IMPORTANT FOR OXYTOCIN RELEASE DURING STRESS

The relative importance of the paraventricular (PVN) and the supraopti c nuclei (SON) for the secretion of oxytocin was evaluated by comparis on of stress-induced oxytocin release under normal conditions, in the absence of vasopressin and/or corticoliberin (CRF). We introduced an i ncomplete anterolateral cut (iALC) around the mediobasal hypothalamus designed to leave intact the SON-neurohypophysial connections but to i nflict damage to the nerve fibers from the PVN. The studies were perfo rmed in conscious cannulated rats using immobilization as the stress s timulus. Stress-induced oxytocin release was found in heterozygous Bra ttleboro rats as well as in homozygous animals lacking vasopressin, ye t in the latter it was less pronounced and in both cases it was preven ted by iALC. In Wistar rats, stress-induced oxytocin release was marke dly reduced after iALC and absent after PVN lesion. Both hypothalamic interventions failed to influence basal oxytocin levels and resulted i n a similar reduction of ACTH release. It is concluded that a function al diversity exists between the hypothalamic magnocellular nuclei. At least in relation to immobilization stress, the PVN is essential for s tress-induced oxytocin release and it is evident that the SON without the PVN cannot preserve oxytocin secretion during stress.