Fos induction in brainstem neurons by intravenous hypertonic saline in the conscious rat.

Experiments were done in conscious rats to investigate the effect of intravenous infusion of hypertonic saline on the induction of the protein Fos, in brainstem neurons. Neurons containing Fos-like immunoreactivity were observed in the caudal nucleus of the solitary tract (NTS), the caudal and rostral ventrolateral medulla, and parabrachial nucleus after an infusion of solutions containing 1.4 M NaCl. Little or no expression of Fos was detected in brainstem neurons after intravenous infusions of either physiological (143 mM) or hypotonic (106 mM) NaCl solutions. These data provide evidence for the involvement of brainstem structures in osmoregulatory functions and suggest that brainstem neuronal circuits that function in cardiovascular regulation may also be shared by those involved in body fluid homeostasis.