Expression of c-fos immunoreactivity in the hypothalamic magnocellular neurons during chronic osmotic stimulations

The immunoreactivity of c-fos protein was transiently detected in magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the rat hypothalamus after intraperitoneal injection of hypertonic NaCl solution. In contrast, c-fos-positive magnocellular neurons were persistently observed in the SON and PVN of the rats which were chronically stimulated by the drinking of hypertonic NaCl solution instead of water or by water deprivation. c-fos immunoreactivity was eliminated in the animals which were allowed to drink tap water for 24 h following the chronic osmotic stimulations. These results suggest that persistent expression of c-fos protein is closely associated with the neural plasticity of the hypothalamic magnocellular neuron.