Behavioral differences between male and female Wistar rats on DRL schedules: effect of stimuli promoting collateral activities.

Female rats are more active than males in open-field procedures. They also make fewer unreinforced responses than males on schedules which maintain low rates of responding (differential reinforcement of low rate responding, DRL). The addition of objects to promote collateral activities facilitates the acquisition of efficient DRL behavior. It was hypothesized that differences in activity levels might underlie the observed sex differences in DRL learning. If females are more likely than males to engage in activities other than lever pressing, the addition of objects to the experimental environment should not as much influence the behavior of females than that of males. Male and female rats were exposed to a DRL 15 sec or a DRL 30 sec schedule, either with or without objects to promote collateral activities. General activity was tested twice in an open-field procedure. Females showed higher activity levels than males in the open-field. They also acquired a DRL task more efficiently than males. The addition of objects facilitated the acquisition of efficient DRL performance in males, but not in females. The results of the present experiments, therefore, suggest that differences in general activity between male and female rats may underlie sex differences in some experimental paradigms.