Involvement of N-methyl-D-aspartic acid receptor activation in oxytocin and vasopressin release after osmotic stimuli in rats

The present study aimed to examine roles of N-methyl-D-aspartic acid (NMDA) receptors in oxytocin and vasopressin release after osmotic stimuli. A non competitive NMDA receptor antagonist, MK-801 (0.2 mg/kg body weight, i.p.), significantly decreased plasma concentrations of oxytocin and vasopressin after hypertonic saline injection (0.3 or 0.6 M NaCl, i.p., 20 ml/kg). By c ontrast, oxytocin release induced by injection of cholecystokinin octapepti de (20 mug/kg, i.p,) was not significantly changed by MK-801. Hypertonic sa line injection increased the number of cells expressing Fos in the supraopt ic nucleus and in the regions anterior and ventral to the third ventricle ( AV3V) regions [the organum vasculosum of the lamina terminalis (OVLT) and m edian preoptic nucleus]. MK-801 decreased the number of cells expressing pr otein in these areas after hypertonic saline injection. A microdialysis met hod showed that a hypertonic saline injection (0.6 M NaCl, 20 ml/kg, i.p.) facilitated glutamic acid release in and near the OVLT. The results support the view that NMDA receptor in the AV3V region modulates in a facilitative fashion the AV3V inputs to the supraoptic neurosecretory neurones.