Oxytocin: neurobiologic considerations and their implications for affective illness.

1. Oxytocin is a nonapeptide hormone first isolated in the central nervous system in the supraoptic and paraventricular nuclei of the hypothalamus. Recent studies show that oxytocin is also found in brain regions outside of the hypothalamus and sites of synthesis have been reported in peripheral steroidogenic organs as well. 2. Oxytocin is released from hypothalamic nerve terminals in the posterior pituitary for distribution in the systemic circulation, where it acts to stimulate uterine contraction during parturition and milk let-down during lactation. 3. Although a definitive role for oxytocin in CNS function has not been elucidated, studies in experimental animals suggest involvement in cognition, tolerance and adaptation, and in complex maternal behaviors. Similarly, although oxytocin's function in steroid-producing tissues is not fully established, recent in vitro data has shown that oxytocin can inhibit androgen and estrogen production, and thus may act in a local regulatory fashion. 4. This selective review will highlight some current ideas regarding the functional significance of oxytocin in the central nervous system and review available data concerning the regulation of oxytocin secretion in humans and its potential role in neuropsychiatric illness.