Involvement of serotonergic systems in the lateral parabrachial nucleus in sodium and water intake: a microdialysis study in the rat.

The present study was carried out to investigate whether 0.3 M NaCl and water intake alters the release of serotonin (5-hydoxytryptamine, 5-HT) in the region of the lateral parabrachial nucleus (LPBN) in freely moving rats. The ingestion of 0.3 M NaCl and water was induced by subcutaneous injections of the diuretic furosemide (FURO, 10 mg/kg) and the angiotensin converting enzyme inhibitor captopril (CAP, 5 mg/kg), and extracellular concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured using intracerebral microdialysis techniques. The intake of 0.3 M NaCl and water significantly enhanced the 5-HT and 5-HIAA levels in the LPBN area. The combined treatment with FURO and CAP elicited significant decreases in the 5-HT and 5-HIAA concentrations in the LPBN area under the condition that 0.3 M NaCl and water are not available for drinking. These results suggest that the serotonergic system in the LPBN area may play an important role in the modulation of sodium appetite and thirst.