Food deprivation and ingestion induce reciprocal changes in neuropeptide Y concentrations in the paraventricular nucleus

Abstract

We have studied the effects on neuropeptide Y (NPY) concentration in six hypothalamic nuclei, viz. medial preoptic area (MPOA), paraventricular nucleus (PVN), median eminence (ME), arcuate nucleus (ARC), ventromedial nucleus (VMN) and dorsomedial nucleus (DMN) of food deprivation (FD) for 2, 3, or 4 days or FD for 4 days followed by one day ad lib food intake (FI) in male rats. Hypothalamic nuclei were microdissected by the technique of Palkovits and processed for measurement of NPY immunoreactivity by RIA. NPY-like immunoreactivity in the ME, VMN and DMN was unaffected by FD or FI, but the remaining three nuclei—the ARC, MPOA and PVN—displayed a different pattern of changes in NPY levels in response to either FD or FD followed by FI. In the ARC, NPY levels rose significantly at day 3 and 4 after FD and remained elevated even after one day of FI. In the MPOA, while FD for 4 days had no effect, NPY concentration increased significantly in response to FI. In contrast, in the PVN, a site implicated in the control of feeding behavior, the NPY response to FD and FI was markedly different. FD elicited a gradual, time-related increase in NPY levels to reach highest concentration on day 4 and thereafter, following one day of FI, NPY levels fell dramatically to the range found in control satiated rats. These results show that (1) NPY levels display site-specific changes in response to FD and FI; (2) a dramatic reciprocal change in the PVN NPY levels occurred in response to disturbances in the daily food intake as produced by sequential FD and FI; (3) other hypothalamic sites, such as the ARC and MPOA, displayed only unidirectional increments in response to FD and FI. The observation of site-specific changes in the PVN NPY levels further support the hypothesis that NPY may be a physiological neurochemical signal in the PVN that normally evokes feeding in the rat.