Ovarian hormones modify anxiety behavior and glucocorticoid receptors after chronic social isolation stress

Abstract

Chronic social isolation could lead to a disruption in the Hypothalamic-Pituitary-Adrenal (HPA) axis, resulting in anxiety and depressive-like behaviors but cycling estrogens could modify these behaviors. The aim of this study was to determine if changes in ovarian hormones during the normal cycle could interact with social isolation to alter anxiety and depressive-like behaviors. In parallel, we examined the expression of glucocorticoid receptor (GR) and synaptic vesicle protein synaptophysin in the hippocampus and hypothalamus of Sprague Dawley normal cycling female rats. We assigned rats to either isolated or paired housing for 8 weeks. To assess anxiety and depressive-like behaviors, we used the open field test and forced swim test, respectively. Female rats were tested at either diestrus, estrus, or proestrus stage of the estrous cycle. After behaviors, rats were perfused and brains collected. Brain sections containing hippocampus and hypothalamus were analyzed using immunohistochemistry for synaptophysin and glucocorticoid receptor (GR) levels. We found an increase in depressive-like behaviors for isolated animals compared to paired housed rats, regardless of the estrous cycle stage. Interestingly, we found a decrease in anxiety behaviors in females in the estrus stage accompanied by a decrease in GR expression in hippocampal DG and CA3. However, no changes in synaptophysin were observed in any of the areas of studied. Our results support the beneficial effects of circulating ovarian hormones in anxiety, possibly by decreasing GR expression.

Keywords: Anxiety; Depression; Estrous cycle; Glucocorticoids; Hippocampus; Social isolation.

Fig. 1

Effects of social isolation and estrous cycle stage (A, B) in locomotion after social isolation or pairing measured by total distance travelled in the Open Field Test. No significant differences were found between isolated and paired rats in locomotion in the 0–5 min interval (A). However, isolated rats showed an increase in locomotion in the 5–10 min interval (B). Data are presented as mean ± SEM distance (cm). * p < 0.05.

Fig. 2

Effects of social isolation and estrous cycle stage in anxiety behaviors measured by time spent in the center in the Open Field Test. Paired females in estrus stage showed an increase in time in the center compared to proestrus and diestrus, suggesting a decrease anxiety (A). For the last five minutes of the test, there were no differences in time spent in the center of the apparatus, suggesting that the rats have habituated (B). Data are presented as mean ± SEM time (s). * p < 0.05.

Fig. 3

Effects of social isolation and estrous cycle stage in depressive-like behaviors measured by total immobility and latency to immobility in the Forced Swim Test. No significant differences were observed in the total immobility time by either isolation or estrous cycle stage (A). However, a main effect of isolation was found, where isolated rats displayed less latency to immobility compared to paired rats. Paired estrus showed an increase in latency to immobility when compared to isolated proestrus (p = 0.04) (B). Data are presented as mean ± SEM time (s). * p < 0.05.

Fig. 4

Effects of social isolation and estrous cycle stage in Glucocorticoid Receptor (GR) expression as measured by average percent area occupied in DG (A), CA3 (B), CA1 (D) and VMH (D). No significant differences were observed in the GR expression for isolated versus paired rats. A main effect for the estrous cycle was found in the DG. Isolated females in diestrus showed a trend to an increase in GR when compared to estrus (A; p = 0.05). Females in the estrus stage showed a decrease in GR expression compared to proestrus in the isolated group and a trend to a decrease for the paired group (B). No differences were found between isolated or paired rats or by estrous cycle stage for the other subareas (C, D). Data are presented as mean ± SEM percent area. * p < 0.05.

Fig. 5

Effects of social isolation and estrous cycle stage in Synaptophysin expression as measured by average percent area immunolabeled in DG (A), CA3 (B), and CA1 (C). No differences were found between isolated or paired rats, or by estrous cycle stage for any subarea of the hippocampus (A, B, C). Data are presented as mean ± SEM of the percent area.