Serotonin 5-HT1A receptor mRNA expression in dorsal hippocampus and raphe nuclei after gonadal hormone manipulation in female rats

Female ovarian steroids influence mood and cognition, an effect presumably mediated by the serotonergic system. A key receptor in this interplay may b e the 5-HT1A receptor subtype. We gave adult ovariectomized female rats sub cutaneous pellets containing different dosages of 17 beta -estradiol alone or in combination with progesterone, or placebo pellets, for 2 weeks. 5-HT1 A receptor mRNA levels were analyzed by in situ hybridization in the dorsal hippocampus, dorsal and median raphe nuclei, and entorhinal cortex. Estrad iol treatment alone reduced 5-HT1A gene expression in the dentate gyrus and the CA2 region (17 and 19% decrease, respectively). Estradiol combined wit h progesterone supplementation increased 5-HT1A gene expression versus plac ebo in the CA1 and CA2 subregions of the dorsal hippocampus (16 and 30% inc rease, respectively). Concomitantly, 5-HT1A mRNA expression was decreased b y 13% in the ventrolateral part of the dorsal raphe nuclei, while no change s were found in the median raphe nucleus and entorhinal cortex. Chronic eff ects of ovarian hormones on 5-HT1A receptor mRNA expression appear tissue-s pecific and involve hippocampal subregions and the raphe nuclei. Modulation of 5-HT1A receptor gene expression may be of importance for gonadal steroi d effects on mood and cognition. Copyright (C) 2001 S.Karger AG, Basel.