Opposite effects of oxytocin and vasopressin on the emotional expression of the fear response.

Oxytocin and vasopressin are two neuropeptides that have been extensively studied for their systemic and physiological roles. Studies in rodents show that oxytocin and vasopressin play an opposite role in several behavioural and physiological tests for anxiety and fear. Their effects on single cell activity in the central amygdala (CeA) triggered a number of electrophysiological studies that allowed us to develop a model of their opposing effects. In our model, GABAergic neurons in the lateral part of the central amygdala are excited by oxytocin and project to the medial part where they inhibit neurons that can be excited by vasopressin. Besides oxytocin and vasopressin, the CeA expresses a large number of other neuropeptide receptors and the question arises if a similar model can apply to their actions. We here develop a hypothesis in which neuropeptides, through their effects on distinct populations in the CeA, affect specific projections and specific physiological expressions of the fear response. Our hypothesis may be of importance for the current interest in neuropeptide receptors as therapeutic targets for neuropsychiatric disorders.