Regional effect of naltrexone in the nucleus of the solitary tract in blockade of NPY-induced feeding

Naltrexone (NLTX) in the nucleus of the solitary tract (NTS) decreases feeding induced by neuropeptide Y (NPY) in the paraventricular nucleus (PVN). We sought to determine the NTS region most sensitive to NLTX blockade of PVN NPY-induced feeding. Male Sprague-Dawley rats were fitted with two cannulas; one in the PVN and one in a hindbrain region: caudal, medial, or rostral NTS or 1 mm outside the NTS. Animals received NLTX (0, 1, 3, 10, and 30 μg in 0.3 μl) into the hindbrain region just prior to PVN NPY (0.5 μg, 0.3 μl) or artificial cerebrospinal fluid (0.3 μl). Food intake was measured at 2 h following injection. PVN NPY stimulated feeding, and NLTX in the medial NTS significantly decreased NPY-induced feeding at 2 h, whereas administration of NLTX in the other hindbrain regions did not significantly influence PVN NPY induced feeding. These data suggest that opioid receptors in the medial NTS are most responsive to feeding signals originating in the PVN after NPY stimulation.