[Sucrose reward promotes rats' motivation for cocaine]

Caloric diet, such as fat and sugar intake, has rewarding effects, and has been indicated to affect the responses to addictive substances in animal experiments. However, the possible association between sucrose reward and the motivation for addictive drugs remains to be elucidated. Thus, we carried out behavioral tests after sucrose self-administration training to determine the effects of sucrose experience on rats' motivation for cocaine, locomotor sensitivity to cocaine, basal locomotor activity, anxiety level, and associative learning ability. The sucrose-experienced (sucrose) group exhibited higher lever press, cocaine infusion and break point, as well as upshift of cocaine dose-response curve in cocaine self-administration test, as compared with the control (chow) group. Additionally, despite similar locomotor activity in open field test and comparable score in cocaine-induced conditioned place preference, the sucrose group showed higher cocaine-induced locomotor sensitivity as compared with the chow group. The anxiety level and the performance in vocal-cue induced fear memory were similar between these two groups in elevated plus maze and fear conditioning tests, respectively. Taken together, our work indicates that sucrose experience promotes the rats' motivation for cocaine.