Sexually dimorphic effects of estrogen on spines in cultures of accessory olfactory bulb.

A sex difference has been reported in the responsiveness of the vomeronasal (VN) system to pheromones. In the present study, to clarify a direct and acute influence of 17β-estradiol (E2) on the accessory olfactory bulb (AOB) neurons, we investigated the effect of E2 on dendritic spines in cultured AOB cells derived from male and female neonatal rats. After 17-18 days in vitro (DIV), cultured AOB cells were transfected with GFP expression vectors. At 21-23 DIV, cells were treated with E2, and time-lapse images of transfected AOB neurons identified as granule cells were taken under a confocal laser scanning microscope for 3h. The dendritic spine head area of granule cells was quantitatively evaluated, and spine heads were classified into larger (≥ 1 μm²) and smaller (<1 μm²) ones before E2-treatment (0 h). In cultured cells derived from both sexes, the larger spines were not significantly changed at 1, 2 and 3 h after E2-treatment. In contrast, E2-treatment significantly enlarged the head area of the smaller spines of granule cells derived from the female, whereas E2 did not cause any significant effects on those from the male. Our results provide evidence for the sexually-dimorphic effect of E2 on spine development in AOB granule cells.