DIVERGENCE OF THE FEEDING AND THERMOGENIC PATHWAYS INFLUENCED BY NPY IN THE HYPOTHALAMIC PVN OF THE RAT

Neuropeptide Y (NPY) injected into the paraventricular nucleus (PVN) i ncreases feeding and decreases brown adipose tissue (BAT) uncoupling p rotein (UCP) and lipoprotein lipase (LPL) mRNA. Previously we reported that the feeding and BAT effects induced by NPY in the PVN are blocke d by 50 mu g naltrexone (NTX) in the rostral nucleus of the solitary t ract (rNTS). We sought to determine whether the effect of rNTS NTX on PVN NPY-induced alterations in energy metabolism occurred at lower dos es of NTX. Male Sprague-Dawley rats were fitted with cannulas into two sites: PVN and rNTS. Feeding response, BAT UCP, and LPL mRNA were mea sured after injection of 0, 5, 10, and 25 mu g NTX in the rNTS +/- 1 m u g NPY in the PVN. One-hour feeding response to PVN NPY was significa ntly and dose dependently decreased by 10 and 25 mu g rNTS NTX (-23 an d -31%, respectively). However, rNTS NTX did not block the PVN NPY-ind uced decrease in BAT UCP or LPL mRNA. BAT p-actin mRNA (as a measure o f overall changes in gene expression) was unchanged among treatment gr oups. These results indicate a possible divergence in the PVN NPY feed ing-stimulatory/BAT-inhibitory pathway, such that PVN NPY feeding effe cts may be routed through the rNTS whereas BAT effects may be due to a lterations at another neural site.