Decreased motivation to eat in mu-opioid receptor-deficient mice.
European Journal of Neuroscience. 2007-06-06; 25(11): 3398-3405
DOI: 10.1111/j.1460-9568.2007.05595.x
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1. Eur J Neurosci. 2007 Jun;25(11):3398-405.
Decreased motivation to eat in mu-opioid receptor-deficient mice.
Papaleo F(1), Kieffer BL, Tabarin A, Contarino A.
Author information:
(1)Laboratoire Homéostasie-Allostasie-Pathologie, EA 3666, Université Victor
Segalen Bordeaux 2, 146 Rue Léo Saignat, 33076 Bordeaux, France.
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 micro-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.
DOI: 10.1111/j.1460-9568.2007.05595.x
PMID: 17553008 [Indexed for MEDLINE]