Behavioural impact of intraseptally released vasopressin and oxytocin in rats

The two nonapeptides arginine vasopressin and oxytocin are not only secrete d from the neurohypophysis into the general circulation but are also releas ed intracerebrally. Our recent research has focused on the release patterns and effects of oxytocin and vasopressin in brain areas, such as the septum and hypothalamus, that are thought to be involved in the regulation of (1) behavioural responses and (2) responses of the hypothalamoneurohypophysial system (HNS) to stressor exposure in rats. The results demonstrate that co mbined physical and emotional stress (induced by exposure to forced swimmin g) selectively triggers the release of vasopressin within all brain areas u nder study but not into the general circulation. Under emotional stress con ditions (induced by exposure to the 'social defeat' procedure), however, ox ytocin rather than vasopressin release increased within the hypothalamus an d septum. Experiments aimed at revealing the neuroendocrine and behavioural relevance of the local nonapeptide release provided evidence for an involv ement of vasopressin in the regulation of HNS activity (within the hypothal amus) and, moreover, in acute stress-coping strategies, anxiety-related beh aviour and learning and memory processes (within the septum). The observed dissociation between central and peripheral nonapeptide release not only su pports the hypothesis that plasma vasopressin and oxytocin concentrations d o not necessarily reflect central release patterns but also suggests vasopr essin and oxytocin neurones are able to independently release their nonapep tide from different parts of their neuronal surface (e.g. From somata/dendr ites vs, axon terminals). This remarkable regulatory capacity provides the basis for an differential involvement of vasopressin, and probably also oxy tocin, in the co-ordination of neuroendocrine activity, emotionality and co gnition at different brain levels to ensure an appropriate behavioural resp onse of the organism to stressful stimuli.