IngentaConnect Decreased motivation to eat in -opioid receptor-deficient mice

Authors: Papaleo, Francesco; Kieffer, Brigitte L.¹; Tabarin, Antoine²; Contarino, Angelo²

Source: European Journal of Neuroscience, Volume 25, Number 11, June 2007 , pp. 3398-3405(8)

Abstract:

Altered motivational processes might participate to the physiopathology of eating-related disorders. The endogenous opioid system is thought to mediate the hedonic properties of food intake. To assess the role for the µ-opioid receptor (MOR) pathway in the motivational properties of food intake, in the present study we tested wild-type and MOR-deficient mice (MOR-/-) in a nose-poke operant paradigm for chow or sucrose pellets. To avoid confounding factors linked to food restriction/deprivation experience, mice were always provided with food ad libitum. Although less MOR-/- than wild-type mice initiated operant behaviour, under a fixed ratio-1 (FR-1) reinforcement schedule the two genotypes showed similar patterns of food-driven nose-poking, indicating preserved cognitive abilities in MOR-deficient mice. However, during FR-3 and progressive ratio (PR) reinforcement experiments, MOR-/- mice showed lower levels of nose-poking for either chow or sucrose pellets than wild-type mice, indicating a crucial role for the MOR pathway in the motivational properties of food intake. Moreover, under the PR reinforcement schedule mice nose-poking for sucrose pellets showed higher genotype-independent breakpoint levels than mice working for chow pellets, indicating that the MOR pathway is not essential for hedonic processing of palatable food intake. Finally, MOR-/- mice did not differ from wild-type mice in the rate of operant responding extinction, further supporting the notion of unaltered cognitive abilities in the MOR-deficient mice. The present findings strongly indicate that the MOR pathway mediates the motivational properties of food intake, but it is not essential for hedonic processing of ingestive behaviour.

Keywords: food; liking; operant behaviour; opioid system; wanting

Document Type: Research article

DOI: 10.1111/j.1460-9568.2007.05595.x

Affiliations: 1: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, UMR7104, Illkirch, France 2: Laboratoire Homéostasie-Allostasie-Pathologie, EA 3666, Université Victor Segalen Bordeaux 2, 146 Rue Léo Saignat, 33076 Bordeaux, France

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Decreased motivation to eat in µ-opioid receptor-deficient mice