Levonorgestrel maintains goal-directed behavior in habit-trained intact female rats

This study examined the effect of levonorgestrel (LNG), a widely used progestin-type contraceptive, on the development of habit in intact female rats. Rats were implanted with subcutaneous capsules that slowly released LNG over the course of the experiment or cholesterol-filled capsules. All female rats underwent operant training followed by reward devaluation to test for habit. One group of females was trained at a level that is sub-threshold to habit, while another group of females was trained to a level well over the habit threshold observed in intact females. The results reveal that all sub-threshold trained rats remained goal-directed irrespective of LGN treatment, suggesting LNG is not advancing habit formation in female rats at this level of reinforcement. However, in rats that were overtrained well above the threshold, cholesterol females showed habitual behavior, thus replicating a portion of our original studies. In contrast, LNG-treated habit-trained rats remained goal-directed, indicating that LNG impedes the development and/or expression of habit following this level of supra-threshold to habit training. Thus, LNG may offset habit formation by sustaining attentional or motivational processes during learning in intact female rats. These results may be clinically relevant to women using this type of hormonal contraceptive as well as in other progestin-based hormone therapies.PMID:38101144 | DOI:10.1016/j.yhbeh.2023.105468
Source: Hormones and Behavior - Category: Endocrinology Authors: Source Type: research