Decreased motivation to eat in mu-opioid receptor-deficient mice.
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.
Papaleo
Francesco
F
Laboratoire Homéostasie-Allostasie-Pathologie, EA 3666, Université Victor Segalen Bordeaux 2, 146 Rue Léo Saignat, 33076 Bordeaux, France.
Kieffer
Brigitte L
BL
Tabarin
Antoine
A
Contarino
Angelo
A
D000818:Animals; D001522:Behavior, Animal; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D004435:Eating / Q000187:drug effects / Q000235:genetics*; D005108:Extinction, Psychological; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009042:Motivation; D017450:Receptors, Opioid, mu / Q000172:deficiency*; D012055:Reinforcement Schedule; D012054:Reinforcement, Psychology; D013395:Sucrose / Q000008:administration & dosage; D013549:Sweetening Agents / Q000008:administration & dosage
D017450:Receptors, Opioid, mu; D013549:Sweetening Agents; D013395:Sucrose