SWIM STRESS TRIGGERS THE RELEASE OF VASOPRESSIN WITHIN THE SUPRACHIASMATIC NUCLEUS OF MALE RATS

The hypothalamic suprachiasmatic nucleus (SCN) is the predominant pace maker of the mammalian brain that generates and controls circadian rhy thms of various endocrine and behavioral processes. Different lines of evidence suggest that stress interferes with the maintenance of such rhythms. As a first approach to investigate whether the neuropeptide a rginine vasopressin (AVP), which shows circadian rhythms of synthesis and release within the SCN, might contribute to this stress-induced al terations in circadian rhythms, we monitored acute effects of swim str ess on the intra-SCN release of AVP in male rats by means of the micro dialysis technique. A 10-min forced swimming session triggered a marke d but relatively short-lasting increase in the intranuclear release of AVP (to approx. 440%). This effect was restricted to the area contain ing predominantly somata and dendrites of vasopressinergic neurons, si nce no changes in AVP release could be measured in one of their major projection areas, the nucleus of the dorsomedial hypothalamus. Our dat a provide evidence that the amount of AVP released within the SCN can vary widely not only in accordance with AVP's intrinsically regulated circadian rhythm but also in response to a physiologically relevant st ressor. In this way, the neuropeptide may contribute to the regulation of endocrine and behavioral rhythms particularly in challenging situa tions associated with resettings of the endogenous clock. (C) 1998 Els evier Science B.V.