The effects of oestrogen and progesterone on serotonin and its metabolite in the lateral septum, medial preoptic area and ventromedial hypothalamic nucleus of female rats

The effects of sex steroid hormones on serotonin and its metabolite, 5-hydr oxyindole-3-acetic acid (5-HIAA) in the lateral septal nucleus (LS), the me dial preoptic area (MPA) and the ventromedial nucleus of the hypothalamus ( VMH) of female rats were investigated, using immunohistochemistry and high- performance liquid chromatography (HPLC). Female rats were divided into thr ee groups: ovariectomized rats (OVX group); OVX-rats treated with estradiol benzoate alone (E2 group); and OVX-rats treated with E2 plus progesterone (E2 + P group). We analysed the density of serotonin-immunoreactive fibres with a computer-assisted image analysis system, and measured the tissue con centrations of serotonin and 5-HIAA. Many serotonin-immunoreactive fibres w ere observed in the LS, MPA and VMH in all three groups. The density of ser otonin-immunoreactive fibres in the MPA and VMH was significantly lower in the E2 and E2 + P groups compared to the OVX group, whereas the LS showed n o detectable differences among the three groups. In the HPLC study,the conc entrations of serotonin in the MPA and VMH of the E2 and E2 + P groups were significantly lower than that in the OVX group, There was no significant d ifference in the concentration of serotonin in the LS, The concentration of 5-HIAA and the ratio of 5-HIAA/serotonin in the LS, MPA and VMH showed no significant differences among the OVX, E2 and E2 + P groups. The present re sults suggest that E2 priming for sexual behaviour can affect the serotoner gic system by decreasing serotonin content, but not the turnover rate, in t he MPA and VMH of female rats.