Interactions Between Leptin and Hypothalamic Neuropeptide Y Neurons in the Control of Food Intake and Energy Homeostasis in the Rat

Leptin acts on the brain to inhibit feeding, increase thermogenesis, and decrease body weight. Neuropeptide Y (NPY)-ergic neurons of the hypothalamic arcuate nucleus (ARC) that project to the paraventricular nuclei (PVN) and dorsomedial nuclei (DMH) are postulated to control energy balance by stimulating feeding and inhibiting thermogenesis, especially under conditions of energy deficit. We investigated whether leptin9s short-term effects on energy balance are mediated by inhibition of the NPY neurons. Recombinant murine leptin (11 μg) injected into the lateral ventricle of fasted adult Wistar rats inhibited food intake by 20–25% between 2 and 6 h after administration, compared with saline-treated controls ( P P P P P > 0.1), but plasma leptin levels were significantly higher (4.88 ± 0.66 vs. 2.85 ± 0.20 ng/ml; P