Sex differences in motivation to take sucrose following abstinence and environmental enrichment in Long-Evans rats.

There are clinically significant sex differences in addiction behaviors. We have previously reported robust sex differences in motivation to consume sucrose in adult Long-Evans rats. In the present study, motivation to consume 10% sucrose was assessed with lever press responding (0.4mL per reinforcement) on a progressive ratio (PR) schedule during daily 3-h sessions for 1 week following either overnight (acute) or 1 month (chronic) environmental enrichment (EE). Acute EE was provided immediately after initial training or after 29 days of abstinence. Males and females were segregated by sex throughout the study. Females responded to higher breakpoints during training and post-EE testing. In both sexes, there was an abstinence-dependent increase (incubation) of PR responding for sucrose in control subjects tested after 1 month vs. 1 day of abstinence. Both acute and chronic EE decreased subsequent breakpoints, but the persistence of the effect differed by sex and length of abstinence. For testing following 1 day of abstinence from sucrose, acute EE with males resulted in decreased breakpoints persisting 3 days. EE-induced reductions in breakpoints for females were not statistically significant. For testing starting after 29 days of abstinence from sucrose, acute EE with males resulted in decreased breakpoints persisting 3 days. Chronic EE with males decreased their breakpoints for 3 days but had no effect on responding by females. EE-induced reductions in breakpoints for females were not statistically significant. Sucrose consumption relative to body weight was reduced by EE for males similar to decreases in breakpoints. For females, acute (both early and late abstinence) and chronic EE also reduced sucrose consumption, but only on the first day of testing. These results replicate our previous findings of greater motivation to consume sucrose by females, demonstrate an incubation of PR responding for both sexes, and an overall more persistent anti-sucrose taking effect of EE with males.