The Dorsal Raphe neurons and the serotonergic modulation of fluid balance.

VIVAS L, GODINO A, CARRER HF, DE LUCA LA JR, MARGATHO LO, BADAUE-PASSOS, D JR, JOHNSON, AK , ANTUNES-RODRIGUES J.

Aguas de Lindoia, San Pablo, Brasil

Simposio; XXIII Annual Meeting of Brazilian Federation Biological Societies (FESBE).; 2008

FESBE

The Dorsal Raphe neurons and the serotonergic modulation of fluid balance. Vivas L, Godino A, Carrer HF, De Luca LA Jr, Margatho LO, Badaue-Passos, D Jr, Johnson, AK , Antunes-Rodrigues J. Instituto Ferreyra, Córdoba, Argentina.   Our previous results indicate that serotonergic neurons of the Dorsal raphe nucleus (DRN) change their activity in response to body sodium status (1,2,3). In these studies we have analyzed the number and distribution of double immunoreativity (Fos-serotonin, 5HT) before and after sodium intake induced by sodium depletion.  Our results indicate that the activity of DRN-5HT neurons is decreased when the animals are sodium depleted and increased when the animals are either in near normal sodium balance or are in the process of restoring sodium homeostasis by ingesting a NaCl solution, regardless the sodium concentration of the solution consumed. Similarly, we have observed that 5HT neurons of the DRN increase their activity after and isotonic blood volume expansion (BVE) (2). Moreover, the number of Fos-5HT cells is further increase following an hypertonic BE (unpublished data). Consistent with these data, previous works (4, 5, 6) have demonstrated that the DRN lesion, as well as the injection of a non-specific serotonin antagonist, Metisergide, at the lateral parabrachial nucleus (LPBN, where DRN serotonergic neurons arrive), increase spontaneous and induced sodium appetite and decrease water and electrolytes renal excretion stimulated by an isotonic BVE. Likewise, the LPBN injection of DOI a 5HT2A/2C  receptor agonist,  produces opposite effects. In addition, our connectional studies demonstrated that neurons located in the Lamina Terminalis projecting to the DRN, are activated in the course of sodium satiety (7).Taking into account this evidence we have also investigated the effect of body sodium status on the electrical activity of serotonergic neurons of the DRN.   With this purpose we have analyzed the firing frequency changes in the 5HT DRN cells after a body sodium overload, employing an “in vivo” single-unit extracellular recording. Our results indicate that the electrical activity of 5HT neurons of the DRN is modulated by changes in plasma osmolality and plasma sodium concentration since the firing frequency of this group of cells increased after sc hypertonic NaCl infusion while sc isotonic NaCl infusion did not caused any effect. Taken together, these results suggest that body sodium levels would modulate the 5HT activity of the DRN, to limit excess NaCl intake and prevent excess volume expansion.   1-Franchini LF, Jonhson AK,de Olmos J,Vivas L. Sodium appetite and Fos activation in serotonergic neurons. Am J Physiol.:282(1):R235-43, 2002. 2-Godino A, Giusti-Paiva A, Antunes-Rodrigues J and Vivas L. Neurochemical Brain Groups Activated After An Isotonic Blood Volume Expansion In Rats. Neuroscience 133:493-505, 2005. 3-Godino A, De Luca LA Jr, Antunes-Rodrigues J, Vivas L Oxytocinergic and serotonergic systems involvement in sodium intake regulation: satiety or hypertonicity markers? Am J Physiol. 293(3):R1027-36, 2007. 4-Margatho LO, Giusti-Paiva A, Menani JV, Elias LL, Vivas LM and Antunes-Rodrigues J. Serotonergic mechanisms of the lateral parabrachial nucleus in renal and hormonal responses to isotonic blood volume expansion. Am J Physiol. 293(3): R1190-R1197, 2007. 5-Menani JV, De Luca LA Jr, Thunhorst RL and Johnson AK. Hindbrain serotonin and the rapid induction of sodium appetite. Am J Physiol 279: R126-R131, 2000. 6-Olivares EL, Costa-E-Sousa RH, Cavalcante-Lima HR, Lima HR, Cedraz-Mercez PL, Reis LC. Effect of electrolytic lesion of the dorsal raphe nucleus on water intake and sodium appetite. Braz J Med Biol Res 36:1709-1716, 2003. 7-Badaue-Passos, D. Jr, Godino, A. Johnson, AK, Vivas, L, Antunes-Rodrigues, J. Dorsal raphe nuclei integrate allostatic information evoked by depletion-induced sodium ingestion. Exp. Neurol. 206:86-94, 2007. Supported by ANPCyT, Conicet, and CnPQ.