Abstract
The subfornical organ (SFO) is involved in the modulation of sodium and water intake in the rat. To clarify whether serotonergic mechanisms in the SFO participate in the modulatory system, experiments were carried out to investigate the effects of sodium and water intake on serotonin (5-hydroxytryptamine, 5-HT) release in the subfornical organ (SFO) in freely moving rats. The intake 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) in the region of the SFO were measured using intracerebral microdialysis techniques. The combined treatment with FURO and CAP produced significant decreases in the 5-HT and 5-HIAA levels in the SFO area. The 0.3 M NaCl and water intake caused by the treatment significantly increased the 5-HT and 5-HIAA concentrations in the SFO area compared with the basal levels. No significant changes in the 5-HT and 5-HIAA levels elicited by either the FURO and CAP treatment or water and NaCl intake were observed in the sites away from the SFO. These results suggest that the serotonergic mechanism in the SFO area may be important for the control of sodium appetite and thirst. [Jpn J Physiol 54 Suppl:S205 (2004)]
