The overall objective of this proposal is to investigate a means by which estrogen and progesterone can modulate central serotonergic transmission, focusing upon the estrogen and progesterone target cells in the dorsal raphe nucleus of the rat brain. The gonadal steroids and sertonin appear to be important mediators of affective mental states, and an imbalance in the concentrations and/or activities of these neurochemicals are implicated in the onset of numerous psychiatric disorders, particularly anxiety and depression. Considering the higher incidence of these disorders among women, especially during low circulating ovarian steroids, the mechanisms by which estrogen and progesterone modulate serotonergic transmission must be elucidated. Published results suggest that ovarian steroid regulation of serotonergic activity involves both local circuitry at the cell bodies, as well as local feedback circuits at the terminal fields. In the rat brain, intracellular estrogen receptors (the alpha isoform) and progestin receptors have been identified within cells of unknown phenotype(s) adjacent to, but not in, serotonergic neurons in the dorsal raphe nucleus, suggesting trans-synaptic interaction. Thus, characterization of the ovarian steroid cells in the dorsal raphe is a necessary step in the path to fully understanding the seemingly complex mediation of serotonergic transmission by estrogen and progesterone. Based upon published results which indicate facilitory and inhibitory actions of these steroids on serotonin activity, and preliminary neurochemical data, I hypothesize that there are at least two populations of steroid responsive cells. Briefly, the specific aims of this project are 1) to identify and characterize the neurochemical properties of the ovarian steroid target cells in the dorsal raphe and 2) to examine sex differences in these properties, and in serotonergic responsiveness to these steroids. Dual-label immunocytochemistry, in situ hybridization histochemistry, and combined in situ hybridization and immunocytochemistry will be used to investigate expression and regulation of predicted transmitters (aspartate, glutamate, and GABA), receptors (estrogen, progestin, 5-HT2A) and transporters (SERT and VMAT2). Identified sex differences will be examined in a developmental study, through gonadal steroid manipulations, to determine whether such dimorphisms are established prenatally or steroid-mediated during early postnatal development.
