Regional hypothalamic differences in neuropeptide Y-induced feeding and energy substrate utilization.

Previous research has shown that both the paraventricular nucleus (PVN) of the hypothalamus and the perifornical hypothalamus (PFH) are sites at which microinjection of neuropeptide Y (NPY) can induce eating. The PVN has also been shown to be responsive to the effects of exogenous NPY on energy substrate utilization. Therefore, the objective of the present study was to further characterize and compare the effects of NPY on whole-body calorimetry and feeding after microinjection into either the PVN or the PFH. The metabolic effects of NPY (19.5-78 pmol) were determined using an open-circuit calorimeter by measuring the volumes of oxygen consumed and carbon dioxide expired in order to compute respiratory quotients (RQs). Following NPY injection into the PVN (n = 10) or PFH (n = 10), RQs and locomotor activity were monitored over three hours. Additional groups of rats with PVN (n = 10) or PFH (n = 10) cannulae were tested for their feeding responses to these same doses of peptide. While NPY injections into the PVN evoked dose-dependent increases in RQ within 30-40 min of treatment, PFH NPY did not alter RQ at any of the doses tested. Locomotor activity was unaffected by NPY in either site. NPY administration into both the PVN and PFH stimulated eating, although the PFH was found to be the more sensitive in terms of absolute amount of food consumed. These findings support the hypothesis that the PVN may regulate metabolic processes that either produce or coincide with NPY-induced feeding. This contrasts with the PFH, which appears to mediate only the feeding-stimulatory actions of NPY.