Neuropeptide Y messenger ribonucleic acid in the magnocellular hypothalamo-neurohypophysial system of the rat is increased during osmotic stimulation

In the magnocellular hypothalamo-neurohypophysial system of the rat, levels of neuropeptide Y (NPY) mRNA were investigated by in situ hybridization histochemistry both in normal and osmotically stimulated animals. As an osmotic stimulus, animals were given 340 mM NaCl to drink for 12 days. After saline treatment, there was a very marked increase in NPY mRNA in the hypothalamic magnocellular supraoptic (SON) and paraventricular (PVN) nuclei (7600% and 3200%, resp.). These data suggest that magnocellular SON and PVN neurons synthesize NPY in response to the physiological stimulus of increased plasma osmolality.