Opioids in the hypothalamus control dopamine and acetylcholine levels in the nucleus accumbens.
The experimental question is whether hypothalamic opioids, known to stimulate consummatory behavior, control a link to the nucleus accumbens (NAc). It was hypothesized that opioids injected in the hypothalamic paraventricular nucleus (PVN) alter the balance of dopamine (DA) and acetylcholine (ACh) in the NAc in a manner that fosters appetite for food or ethanol. Rats were implanted with two guide shafts, one in the NAc to measure extracellular DA and ACh by microdialysis and the other in the PVN for microinjection of opioid mu- and delta-agonists, an antagonist, or saline vehicle. The compounds tested were morphine, the mu-receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin (DAMGO), the delta-receptor agonist D-Ala-Gly-Phe-Met-NH2 (DALA), and the opioid antagonist naloxone methiodide (m-naloxone). Morphine in the PVN increased the release of accumbens DA (+41%) and decreased ACh (-35%). Consistent with this, the opioid antagonist m-naloxone decreased DA (-24%) and increased ACh (+19%). In terms of receptor involvement, DAMGO dose-dependently increased DA to up to 209% of baseline. Simultaneously, ACh levels were markedly decreased to 55% of baseline. The agonist DALA produced a smaller but significant, 34% increase in DA, without affecting ACh. In contrast, control injections of saline had no significant effect. These results demonstrate that mu- and delta-opioids in the PVN contribute to the control of accumbens DA and ACh release and suggest that this circuit from the PVN to the NAc may be one of the mechanisms underlying opiate-induced ingestive behavior as well as naltrexone therapy for overeating and alcoholism.
Rada
Pedro
P
Laboratory of Behavioral Physiology, School of Medicine, University of Los Andes, Mérida, Venezuela.
Barson
Jessica R
JR
Leibowitz
Sarah F
SF
Hoebel
Bartley G
BG
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000109:Acetylcholine / Q000378:metabolism*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D006719:Homovanillic Acid / Q000378:metabolism; D008297:Male; D017551:Microdialysis / Q000379:methods; D008845:Microinjections / Q000379:methods; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009714:Nucleus Accumbens / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D015102:3,4-Dihydroxyphenylacetic Acid; D009270:Naloxone; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D009020:Morphine; D000109:Acetylcholine; D004298:Dopamine; D006719:Homovanillic Acid