Ward HG, Simansky KJ. Chronic prevention of mu-opioid receptor (MOR) G-protein coupling in the pontine parabrachial nucleus persistently decreases consumption of standard but not palatable food.
Psychopharmacology (Berl) 2006;
187:435-46. [PMID:
16847679 DOI:
10.1007/s00213-006-0463-7]
[Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Accepted: 05/29/2006] [Indexed: 12/01/2022]
Abstract
RATIONALE
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.
OBJECTIVES
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.
MATERIALS AND 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.
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