?Participation of serotonergic and oxytocinergic systems on sodium intake regulation.?

GODINO, A.; J. ANTUNES-RODRIGUES; DE LUCA, LA JR,; L. VIVAS

Buenos Aires, Argentina

Congreso; XXII Congreso Latinoamericano y 1ro Iberoamericano de Ciencias Fisiológicas; 2006

Participation of serotonergic and oxytocinergic systems on sodium intake regulation. ¹Godino, A.;²Antunes-Rodrigues, J.;3De Luca, LA Jr, ¹Vivas, L. ¹INIMEC, Cba., Argentine.²Physiology Dept.,USP, Physiol. and Pathol. Depts., UNESP Brazil. Our studies demonstrated the inhibitory participation of the serotonergic (5HT) and oxytocinergic (OT) systems on sodium appetite induced by peritoneal dialysis (PD). In this model the activity of 5HT neurons increased after 2% NaCl intake and decreased when the animals were sodium depleted; however, the activity of the OT neurons appeared only after 2% NaCl intake. This effect would not be specifically associated with an inhibitory influence of oxytocin on sodium appetite; maybe it would be a consequence of the OT system stimulation by means of hypernatremic signals. The aim of this study was to discriminate whether the activation of the 5HT and OT neurons observed in our paradigm is the result of sodium satiation process or the stimulation induced by hypertonic sodium ingestion. Adult male Albino rats were sodium depleted by PD. Twenty-four hours after PD or Control peritoneal dialysis (CD), the groups had access to 2% NaCl (CD 2% and PD 2% groups) or 0.9% NaCl (CD 0.9% and  PD 0.9% groups) drinking test. Rats were decapitated and bled after drinking and OT plasma levels were measured by RIA. Another group was perfused for immunohistochemical detection of Fos, Fos-5HT and Fos-OT, 90 min. after drinking. Sodium intake induced by PD significantly increased the number of Fos-5HT cells (P<0.001), independent of NaCl concentration of fluid consumed. In contrast, the number of Fos-OT neurons, increased after 2% NaCl intake (P<0.05) but did not change after 0.9% NaCl ingestion. The OT plasma levels significantly increased in PD 2% groups compared to others showing a synergic effect of both factors (P<0.05). In summary, 5HT neurons were stimulated after body sodium status reestablishment consistent with the idea that this system is activated under conditions of satiety. In relation to the OT system both, the OT neural activity and the OT plasma levels were increased by the entering of hypertonic NaCl solution during sodium consumption, suggesting that this system is involved  in the processing of hyperosmotic signals.   Supported by CONICET, ANPCyT and CNPq.