Effects of opioid antagonists naloxone and naltrexone on neuropeptide Y-induced feeding and brown fat thermogenesis in the rat. Neural site of action.
Neuropeptide Y administered intracerebroventricularly and into the paraventricular nucleus of the hypothalamus stimulates feeding and decreases brown adipose tissue thermogenesis. Although specific neuropeptide Y antagonists are not yet available, previous studies had shown that the opioid antagonist naloxone blocked neuropeptide Y-induced feeding when both drugs were injected intracerebroventricularly. We wanted to find out if naloxone injected into specific brain sites would block neuropeptide Y effects on feeding and brown fat thermogenesis. Rats were double injected in specific brain sites with neuropeptide Y and either naloxone or naltrexone (a congener of naloxone). Food intake and brown fat measures were assessed. Naloxone or naltrexone in the paraventricular nucleus weakly decreased paraventricular nucleus neuropeptide Y-induced feeding and did not affect neuropeptide Y-induced reductions in brown fat activity. Peripheral naloxone blocked intracerebroventricular neuropeptide Y-induced feeding and brown fat alterations. Fourth ventricular naloxone decreased paraventricular nucleus neuropeptide Y-induced feeding, and naltrexone given into the nucleus of the solitary tract blocked paraventricular nucleus neuropeptide Y-induced alterations in feeding and brown fat. These data indicate that neuropeptide Y in the paraventricular nucleus may act on feeding and brown fat thermogenesis through opioidergic pathways in the nucleus of the solitary tract.
Kotz
C M
CM
Department of Food Science and Nutrition, University of Minnesota, Saint Paul 55108, USA.
Grace
M K
MK
Briggs
J
J
Levine
A S
AS
Billington
C J
CJ
D002001:Adipose Tissue, Brown / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000187:drug effects*; D004734:Energy Metabolism / Q000187:drug effects*; D005247:Feeding Behavior / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology*; D009478:Neuropeptide Y / Q000494:pharmacology*; D009765:Obesity / Q000209:etiology; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017552:Solitary Nucleus / Q000187:drug effects
D009478:Neuropeptide Y; D009270:Naloxone; D009271:Naltrexone