The role of
neuropeptide Y (NPY) in the central control of appetite and energy balance is now established, but its involvement in the control of drinking and fluid homeostasis is less well characterized. Central administration of NPY stimulates drinking in rats, an effect believed to be independent of its orexigenic effects. Recent studies have demonstrated increased
preproneuropeptide Y (preproNPY)
mRNA in the arcuate nucleus (
ARC) of the rat following food deprivation (FD) or water deprivation (WD). Because WD also suppresses food intake, it was not clear whether the osmotic or the
anorectic effects of this stimulus were responsible for increased
ARC preproNPY
mRNA. In an attempt to distinguish between these possibilities, the present study further examined the effects of hyperosmotic stimuli on preproNPY
mRNA in the
ARC.
Salt loading (4 or 7 days) and WD (4 days) both increased the abundance of preproNPY
mRNA in the
ARC. These increases were proportional to the severity and
duration of treatment and were related to the degree of
anorexia and
weight loss. In a separate study WD, FD, or combined food and water deprivation (4 days) all produced similar decreases in
body weight, but WD produced a smaller increase in
ARC preproNPY
mRNA. All of these treatments resulted in the appearance of NPY-like immunoreactivity in
ARC neuronal perikarya. Together these findings suggest that NPY neuron activity in the
ARC may be regulated by decreases in food intake rather than changes in
body weight per se or increased osmolarity and support other data implicating NPY in the central regulation of energy homeostasis.