Involvement of NMDA receptor mechanisms in the modulation of serotonin release in the lateral parabrachial nucleus in the rat

Microdialysis was employed to investigate whether N-methyl-d-asparatate (NMDA) glutamate receptor mechanisms are involved in the modulation of serotonin (5-hydoxytryptamine, 5-HT) release in the region of the lateral parabrachial nucleus (LPBN) in freely moving rats. Perfusion of NMDA (10 and 50 μM) through the microdialysis probe significantly enhanced extracellular concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the LPBN area. Local perfusion of the NMDA antagonist dizocilpine (MK801, 10 and 50 μM) did not change the basal 5-HT and 5-HIAA levels in the LPBN area. MK801 (10 μM) administered together with NMDA antagonized the stimulant effect of NMDA (10 μM). The intake of 0.3 M NaCl and water induced by subcutaneous injections of the diuretic furosemide (FURO, 10 mg/kg) and the angiotensin converting enzyme inhibitor captopril (CAP, 5 mg/kg) produced significant increases in the 5-HT and 5-HIAA concentrations in the LPBN area. The increased levels of 5-HT and 5-HIAA caused by the combined treatment with FURO and CAP were attenuated by perfusion of MK801 (10 μM). These results indicate the participation of NMDA receptors in the control of 5-HT release in the LPBN area.