Plasma oxytocin concentration and paraventricular neurone activity in rats with diencephalic islands and intact brains.

1. Plasma oxytocin concentrations and the discharge rates of identified paraventricular neurones were compared in intact animals and diencephalic island preparations.2. Substantial amounts of oxytocin (88-322 muu./ml.) were found in the plasma of intact rats but in no case was it detected in the plasma of island preparations. The discharge rate of paraventricular units was also significantly reduced in these preparations.3. The results are consistent with the hypothesis that an increase in the discharge rate of paraventricular neurones is associated with oxytocin release from the neurohypophysis.4. The discharge rates of identified paraventricular units were not affected by intravenous injections of oxytocin either in intact animals or island preparations.