Distribution of Fos immunoreactivity in rat brain after sodium consumption induced by peritoneal dialysis.

Fos immunoreactivity was used to map the neuronal population groups activated after sodium ingestion induced by peritoneal dialysis (PD) in rats. Oxytocin immunoreactivity in combination with Fos immunoreactivity was also analyzed to evaluate whether the oxytocinergic neurons of the paraventricular nucleus of the hypothalamus (PVN) are activated during the satiety process of sodium appetite. Sodium ingestion stimulated by PD produced Fos immunoreactivity within defined cells groups of the lamina terminalis and hindbrain areas such us the nucleus of the solitary tract, area postrema, and lateral parabrachial nucleus. On the other hand, particular parvocellular and magnocellular oxytocinergic subdivisions of the PVN and supraoptic nucleus were double labeled after PD-induced sodium consumption. Approximately 27 and 2.1%, respectively, of the activated dorsomedial cap and parvocellular posterior subnuclei of the PVN, which project to the hindbrain, were oxytocinergic. Our data indicate that specific neuronal groups are activated during the satiety process of sodium appetite, suggesting they may form a circuit subserving sodium balance regulation. They also support a functional role for the oxytocinergic neurons in this circuit.