RATIONALE: Previous work has shown that stimulation of GABAergic, opioid, or dopaminergic systems within the nucleus accumbens modulates food intake and food-seeking behavior. However, it is not known whether such stimulation mimics a motivational state of food deprivation that commonly enables animals to learn a new operant response to obtain food. OBJECTIVES: In order to address this question, acquisition of lever pressing for food in hungry animals was compared with acquisition in non-food-deprived rats subjected to various nucleus accumbens drug treatments. METHODS: All animals were given the opportunity to learn an instrumental response (a lever press) to obtain a food pellet. Prior to training, ad lib-fed rats were infused with the gamma-aminobutyric acid (GABA)A agonist muscimol (100 ng/0.5 microl per side) or the mu-opioid receptor agonist D-Ala2, N-me-Phe4, Gly-ol5-enkephalin (DAMGO, 0.25 microg/0.5 microl per side), or saline into the nucleus accumbens shell (AcbSh). The indirect dopamine agonist amphetamine (10 microg/0.5 microl per side) was infused into the AcbSh or nucleus accumbens core (AcbC) of ad lib-fed rats. An additional group was food deprived and infused with saline in the AcbSh. Chow and sugar pellet intake responses after drug treatments were also evaluated in free-feeding tests. RESULTS: Muscimol, DAMGO, or amphetamine did not facilitate acquisition of lever pressing for food, despite clearly increasing food intake in free-feeding tests. In contrast, food-deprived animals rapidly learned the task. CONCLUSIONS: These findings suggest that pharmacological stimulation of any of these neurochemical systems in isolation is insufficient to enable acquisition of a food-reinforced operant task. Thus, these selective processes, while likely involved in control of food intake and food-seeking behavior, appear unable to recapitulate the conditions necessary to mimic the state of negative energy balance.
RATIONALE: Previous work has shown that stimulation of GABAergic, opioid, or dopaminergic systems within the nucleus accumbens modulates food intake and food-seeking behavior. However, it is not known whether such stimulation mimics a motivational state of food deprivation that commonly enables animals to learn a new operant response to obtain food. OBJECTIVES: In order to address this question, acquisition of lever pressing for food in hungry animals was compared with acquisition in non-food-deprived rats subjected to various nucleus accumbens drug treatments. METHODS: All animals were given the opportunity to learn an instrumental response (a lever press) to obtain a food pellet. Prior to training, ad lib-fed rats were infused with the gamma-aminobutyric acid (GABA)A agonist muscimol (100 ng/0.5 microl per side) or the mu-opioid receptor agonist D-Ala2, N-me-Phe4, Gly-ol5-enkephalin (DAMGO, 0.25 microg/0.5 microl per side), or saline into the nucleus accumbens shell (AcbSh). The indirect dopamine agonist amphetamine (10 microg/0.5 microl per side) was infused into the AcbSh or nucleus accumbens core (AcbC) of ad lib-fed rats. An additional group was food deprived and infused with saline in the AcbSh. Chow and sugar pellet intake responses after drug treatments were also evaluated in free-feeding tests. RESULTS:Muscimol, DAMGO, or amphetamine did not facilitate acquisition of lever pressing for food, despite clearly increasing food intake in free-feeding tests. In contrast, food-deprived animals rapidly learned the task. CONCLUSIONS: These findings suggest that pharmacological stimulation of any of these neurochemical systems in isolation is insufficient to enable acquisition of a food-reinforced operant task. Thus, these selective processes, while likely involved in control of food intake and food-seeking behavior, appear unable to recapitulate the conditions necessary to mimic the state of negative energy balance.
Authors: E J Marijke Achterberg; Linda W M van Kerkhof; Michela Servadio; Maaike M H van Swieten; Danielle J Houwing; Mandy Aalderink; Nina V Driel; Viviana Trezza; Louk J M J Vanderschuren Journal: Neuropsychopharmacology Date: 2015-07-15 Impact factor: 7.853
Authors: Morgane Milienne-Petiot; James P Kesby; Mary Graves; Jordy van Enkhuizen; Svetlana Semenova; Arpi Minassian; Athina Markou; Mark A Geyer; Jared W Young Journal: Neuropharmacology Date: 2016-10-11 Impact factor: 5.250