Gonadectomy maintains goal-directed responding in female rats and accelerates habit formation in male rats.

Abstract

We have previously demonstrated that gonadally intact female rats become habitual following around 120 response-outcome (R-Os) exposures during operant training. This rapid development of habit does not occur in gonadally intact male rats, which remain goal-directed up to at least 320 R-Os. The present study sought to examine the effect of removing gonadal hormones on the acquisition and expression of goal-directed and habitual behaviors separately in both male and female rats. To accomplish this, separate experimental groups of adult Long-Evans rats were utilized, including intact and ovariectomized (OVX) females, as well as intact and castrated (CAST) males. All groups were trained to 240 R-Os, and one half of each experimental group was subjected to a reinforcer devaluation procedure, while the remaining half served as nondevalued controls. An extinction test was then used to determine habitual versus goal-directed behavior. Results found intact females trained to 240 R-Os showed habit and intact males trained to 240 R-Os showed goal-directed behavior. Results also found that ovariectomy disrupts habit in female rats, keeping them goal-directed at 240 R-Os, while castration in male rats produced habitual responding at 240 R-Os, thus effectively reversing the sex differences observed in intact rats at 240 R-Os. An additional experiment was done in OVX and CAST males trained to 160 R-Os to determine if gonadectomy altered goal/habit behavior earlier in instrumental learning. Results showed that both OVX females and CAST males were goal-directed at 160 R-Os. Overall, these results indicate the lack of ovarian hormones effectively delays habit in female rats, and lack of testicular hormones produces earlier habit in males. (PsycInfo Database Record (c) 2025 APA, all rights reserved).