Sodium overload modulates the electrical activity of serotonergic (5HT) neurons of the dorsal raphé nucleus (DRN)

Abstract

Our previous results indicate that 5HT neuronal activity (as shown by Fos expression) within the DRN is modulated by body sodium status. The effect of body sodium overload on spontaneous firing frequency of the 5HT‐DRN neurons was analyzed.Male Wistar rats were anesthetized, and a catheter was inserted in the yugular vein; subsequently, a micropipette was stereotaxically lowered into the DRN in order to record single cell extracellular action potentials. After recording basal activity for 3 min, a group of rats received a sc injection of 2M NaCl solution (1.7 ml/min), and a second group of animals received an equal volume of 0.15 M NaCl. Fifteen minutes later we determined the neuronal phenotype by iv infusion of fluoxetine. To measure plasma sodium and osmolality other rats were submitted to the same protocol but were decapitated and bled 0, 5, 10 and 15 min after NaCl infusion.Four min after 2M NaCl infusion, neuronal activity increased significantly compared to the 0.15M NaCl group and basal recording activity. 0.15M NaCl infusion produced no change in spontaneous firing rate. Plasma sodium and osmolality significantly increased after 2M NaCl infusion compared to 0.15M NaCl group and baseline levels.We conclude that hypernatremic systemic states increase the firing rate of 5HT‐DRN cells, possibly to modulate sodium and water intake/excretion and avoid an extracellular volume expansion.Supported by ANPCyT CONICET.