A reevaluation of the relation between estrogen and emotionality in female rats.

It has been hypothesized that the emotionality of the female rat is reduced at estrus. In confirmation of previous research, it was found that administration of estradiol benzoate (EB;20 mug/kg) to female rats of the Maudsley Reactive (MR) strain increased open-field activity and decreased open-field defecation. In addition, ovariectomy increased open-field defecation in MR females. Supporting the generality of these findings, hormone administration reduced open-field defecation and increased open-field activity in intact females of a genetically heterogeneous background. Additional studies suggested that the decrease in open-field defecation at estrus is dependent on estrogenic suppression of food intake. Hormone replacement decreased food intake in the period preceding the open-field test, and colonic contents were also lower in rats treated with EB+P (progesterone) immediately after the completion of the open-field test. These changes were seen in both MR and genetically heterogeneous females. It was concluded that the decrease in open-field defecation at estrus may be mediated by a reduction in food intake and a consequent decrease in colonic contents and that the validity of the defecation response as a measure of emotionality may be seriously questioned under these circumstances.