Chronic prevention of mu-opioid receptor (MOR) G-protein coupling in the pontine parabrachial nucleus persistently decreases consumption of standard but not palatable food.
BACKGROUND
Acute pharmacological studies implicate mu-opioid receptors (MORs) in the parabrachial nucleus (PBN) of the brainstem in modulating eating. The long-term effects of preventing the cellular function of parabrachial MORs on food consumption remain to be elucidated.


OBJECTIVE
To determine whether (1) chronic inhibition of MOR-mediated G-protein coupling in the PBN of rats would persistently reduce eating and (2) food properties dictate the effects of MOR blockade.


METHODS
We microinfused the irreversible MOR antagonist, beta-funaltrexamine (beta-FNA) into the lateral PBN and measured the intake of standard and calorically dense palatable chow for 1 week. First, rats were given standard chow for 20 h daily and a calorically dense palatable chow for 4 h during the day. We infused the agonist, [D: -Ala(2), N-Me-Phe(4), Glycinol(5)]-Enkephalin (DAMGO), 1 week after beta-FNA to probe the acute effects of exogenous stimulation of MORs on palatable food intake. [(35)S]GTPgammaS autoradiography quantified regional loss of MOR cellular function. Next, we measured the actions of beta-FNA on food intake in rats given only standard or palatable chow for 1 week.


RESULTS
One infusion of beta-FNA persistently decreased consumption of standard but not palatable chow, regardless of feeding regimen. beta-FNA also blocked DAMGO-stimulated palatable chow intake, prevented DAMGO-stimulated G-protein coupling in the central and external lateral subnuclei of the PBN, and decreased coupling in the medial PBN. beta-FNA did not affect kappa-opioid receptors.


CONCLUSIONS
MORs in the lateral PBN serve a physiological role in stimulating consumption of standard food. Properties of the diet, such as high palatability or caloric density, may override the influence of inhibiting MOR function.
Ward
Heather G
HG
Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
Simansky
Kenny J
KJ
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002940:Circadian Rhythm; D004435:Eating / Q000187:drug effects*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D005247:Feeding Behavior / Q000187:drug effects*; D005518:Food Preferences / Q000187:drug effects*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008297:Male; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D011149:Pons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors
D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D043562:Receptors, G-Protein-Coupled; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009271:Naltrexone; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C024524:beta-funaltrexamine; D019204:GTP-Binding Proteins