Serotonergic neurones in the dorsal raphe nucleus that project into the medial preoptic area contain oestrogen receptor beta

Serotonin is involved in female sexual behaviour in which the medial preopt ic area (MPA) has a pivotal role. The present study used immunohistochemist ry, in situ hybridization and retrograde transport analysis to investigate whether serotonin neurones in the dorsal raphe nucleus (DRN) of females pro jecting into the MPA contained oestrogen receptor alpha or beta. The projec tion of serotonin neurones from the DRN to the MPA was confirmed using the microinjection of Fluoro-Gold (FG), a fluorescent retrograde tracer, into t he MPA of ovariectomized (OVX-group) and OVX-rats treated with oestradiol b enzoate (E2-group). A number of serotonin neurones in the DRN were labelled with FG, indicating that these serotonin neurones in DRN project their ter minals into the MPA. FG-labelled serotonin neurones expressed ER beta mRNA in the DRN, and the number of the serotonin neurones containing ER beta mRN A between the OVX-group and the E2-treated group was not significantly diff erent. Serotonin neurones in the DRN did not express ER alpha -immunoreacti vity. Since previous findings showed that the density of serotonin-immunore active fibres and the concentration of serotonin within the MPA was signifi cantly lower in the E2-group than the OVX-group, our present observations s uggested that the regulatory effects of E2 on the serotonergic neurone syst em in the MPA may be via ER beta within the serotonin-containing cells in t he DRN of female rats.