Oxytocin in the central nervous system and sexual behaviour in male rats.

Concentrations of oxytocin (OT) and vasopressin (AVP) were measured in cerebrospinal fluid (CSF) obtained from the cisterna magna of freely moving rats. Basal levels of OT and AVP were approximately 9 fmol/ml in both male and female. In the male rats this increased to approximately 18 fmol/ml 5 min after ejaculation, and 27 fmol/ml 20 min after ejaculation. No increase from basal levels occurred when males were placed with unreceptive females, or alone in the test environment. AVP levels were unchanged in any condition. Preliminary investigations indicate that discrete electrolytic lesions to the lateral and posterior parvocellular hypothalamic paraventricular nucleus (PVN) abolished this ejaculation-associated increase in CSF OT, prolonged mount and intromission latencies and reduced the absolute postejaculatory interval (PEI). We conclude that intracerebrally projecting OT systems may be activated during coitus and may contribute to the mechanisms underlying postejaculatory refractoriness.