17Beta-oestradiol modulates glucocorticoid, neural and behavioural adaptations to repeated restraint stress in female rats

Abstract

Sex steroids have a role in modulating responses that extends beyond reproduction. The current study investigated the influence of the sex steroid 17beta-oestradiol on hypothalamic-pituitary-adrenal (HPA) and behavioural responses to acute or repeated restraint stress. Ovariectomized rats treated with 17beta-oestradiol or peanut oil via a subcutaneous silastic capsule were subjected to daily handling (non stressed), acute (single, 1 h) or daily (10 days, 1 h/day) restraint stress. Blood collected at the end of stress revealed that 17beta-oestradiol treatment augmented the corticosterone response to acute restraint. After daily exposure to restraint, the corticosterone response was noticeably diminished in untreated females but 17beta-oestradiol-treated rats still showed an exaggerated response compared to castrated, untreated females. Brain tissue collected 3 h after the end of restraint was probed using isotopic in situ hybridization for corticotropin-releasing factor (CRF) and vasopressin gene expression in the paraventricular nucleus (PVN) of the hypothalamus. 17beta-oestradiol treatment at the higher dose (120 microg/ml) decreased basal CRF mRNA. Stress caused an increase in CRF mRNA expression in 17beta-oestradiol-treated rats but not in the vehicle group. Repeated restraint stress caused an increase in PVN parvocellular vasopressin gene expression, which was more pronounced in 17beta-oestradiol-replaced rats. Animals were exposed to the elevated plus maze for 5 min as a test for anxiety. Non-stressed control rats with or without 17beta-oestradiol replacement spent the same percentage amount of time exploring the open arms of the maze. Previous exposure to acute restraint stress caused a marked reduction in the time spent exploring the open arms, indicating an increase in anxiety levels in these rats; this effect was observed in both vehicle and 17beta-oestradiol-treated rats. After repeated restraint stress, 17beta-oestradiol-replaced rats spent as much time exploring the open arms of the maze as controls, indicating adaptation. By contrast, nonreplaced rats were still showing a significant reduction in open arm exploration after repeated restraint. The present study presents novel data showing that the HPA axis remains reactive to repeated stress in 17beta-oestradiol-treated ovariectomized rats, but stress-induced anxiety behaviour is reduced.

Fig. 1

Effect of 17β-oestradiol treatment on adaptation of the corticosterone response to stress. □, Vehicle; , 120 μg/ml 17β-oestradiol *Significantly different from corresponding vehicle group; +significantly different from control group (P < 0.05, Bonferroni).

Fig. 2

Effect of 17β-oestradiol treatment on paraventricular nucleus mRNA expression 3 h after acute or repeated restraint stress. □, vehicle; , 40 μg/ml 17β-oestradiol; ■, 120 μg/ml 17β-oestradiol. (a) basal corticotropin-releasing factor (CRF) mRNA levels were significantly lower in rats receiving 120 μg/ml 17β-oestradiol implants. (b) After repeated restraint, there was an increase in parvocellular cells expressing vasopressin mRNA. Animals with 120 μg/ml 17β-oestradiol implants had significantly higher counts of vasopressin expressing parvocellular cells compared to vehicle. (*P < 0.05 and ⁺P < 0.001, Bonferroni).

Fig. 3

Effect of 17β-oestradiol treatment on corticotropin-releasing factor (CRF) expression in the paraventricular nucleus after restraint stress. Lightfield photomicrographs of CRF mRNA in situ hybridization signal in representative sections. Veh, Vehicle; E₂, 17β-oestradiol.

Fig. 4

Effect of 17β-oestradiol treatment on vasopressin expression in the PVN after restraint stress. Darkfield photomicrographs of vasopressin mRNA in situ hybridization signal in representative sections. Veh, Vehicle; E₂, 17β-oestradiol; m, magnocellular cell; p, parvocellular cell.

Fig. 5

Effect of restraint stress and 17β-oestradiol on plus maze behaviour. □, Vehicle; , 120 μg/ml 17β-oestradiol. +Significantly different from vehicle control; *significantly different from vehicle repeated restraint group (P < 0.05, Bonferroni).