Intravenous hypertonic saline induces Fos immunoreactivity in neurons throughout the lamina terminalis.

Expression of Fos, the protein product of c-fos, was studied immunohistochemically in the forebrain of rats infused intravenously with hypertonic solutions. Intravenous 1.5 or 0.75 mol/l NaCl or 1.2 mol/l sucrose in 0.15 mol/l NaCl, but not isotonic 0.15 mol/l NaCl, caused increased Fos expression in the hypothalamic paraventricular and supraoptic nuclei and throughout the lamina terminalis (organum vasculosum laminae terminalis, median preoptic nucleus and subfornical organ). These results show that neurons in the lamina terminalis are activated by physiological increases in plasma tonicity and support an involvement of the lamina terminalis in osmoregulation.