Behavioural impact of intraseptally released vasopressin and oxytocin in rats

The two nonapeptides arginine vasopressin and oxytocin are not only secreted from the neurohypophysis into the general circulation but are also released 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 hypothalamo-neurohypophysial system (HNS) to stressor exposure in rats. The results demonstrate that combined physical and emotional stress (induced by exposure to forced swimming) selectively triggers the release of vasopressin within all brain areas under study but not into the general circulation. Under emotional stress conditions (induced by exposure to the 'social defeat' procedure), however, oxytocin rather than vasopressin release increased within the hypothalamus and septum. Experiments aimed at revealing the neuroendocrine and behavioural relevance of the local nonapeptide release provided evidence for an involvement of vasopressin in the regulation of HNS activity (within the hypothalamus) and, moreover, in acute stress-coping strategies, anxiety-related behaviour and learning and memory processes (within the septum). The observed dissociation between central and peripheral nonapeptide release not only supports the hypothesis that plasma vasopressin and oxytocin concentrations do not necessarily reflect central release patterns but also suggests vasopressin and oxytocin neurones are able to independently release their nonapeptide from different parts of their neuronal surface (e.g. from somata/dendrites vs. axon terminals). This remarkable regulatory capacity provides the basis for an differential involvement of vasopressin, and probably also oxytocin, in the co-ordination of neuroendocrine activity, emotionality and cognition at different brain levels to ensure an appropriate behavioural response of the organism to stressful stimuli.