Delta-9-tetrahydrocannabinol enhances food reinforcement in a mouse operant conflict test
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Cannabinoid compounds are known to regulate feeding behavior by modulating the hedonic and/or the incentive properties of food.
The aim of this work was to determine the involvement of the cannabinoid system in food reinforcement associated with a conflict situation generated by stress.
Mice were trained on a fixed ratio 1 schedule of reinforcement to obtain standard, chocolate-flavored or fat-enriched pellets. Once the acquisition criteria were achieved, the reinforced lever press was paired with foot-shock exposure, and the effects of Δ9-tetrahydrocannabinol (THC; 1 mg/kg) were evaluated in this conflict paradigm.
THC did not modify the operant response in mice trained with standard pellets. In contrast, THC improved the instrumental performance of mice trained with chocolate-flavored and fat-enriched pellets. However, the cannabinoid agonist did not fully restore the baseline responses obtained previous to foot-shock delivery. THC ameliorated the performance to obtain high palatable food in this conflict test in both food-restricted and sated mice. The effects of THC on food reinforcement seem to be long-lasting since mice previously treated with this compound showed a better recovery of the instrumental behavior after foot-shock exposure.
These findings reveal that the cannabinoid system is involved in the regulation of goal-directed responses towards high palatable and high caloric food under stressful situations.
KeywordsFood reinforcement THC Operant behavior Foot-shock Palatability Stress Mice
This work was supported by the US National Institutes of Health–National Institute of Drug Abuse (NIH–NIDA) (no. 5R01-DA016768), the Spanish “Ministerio de Educación y Ciencia” (no. SAF2007-64062), the DG Research of the European Commission (GEN-ADDICT, no. LSHM-CT-2004-05166; and PHECOMP, no. LSHM-CT-2007-037669), the “Generalitat de Catalunya-DURSI” (# 2005SGR00131 and ICREA Academia) and the Spanish “Instituto de Salud Carlos III” (no. RD06/001/001). M.F.B. was supported by a post-doctoral fellowship from Fyssen Foundation. E.M.G. was supported by a post-doctoral fellowship from the Spanish “Instituto de Salud Carlos III”. We thank Dr. Patricia Robledo for stylistic revision of the manuscript.
Conflict of interest statement
R. Maldonado has received research grants from Sanofi-Aventis, Esteve, and Ferrer. Neither of the other authors have relevant financial interests to disclose, nor a conflict of interest of any kind.
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