The Blaustein lab investigates the cellular and neuroanatomical mechanisms of ovarian steroid hormone action on reproductive behavior and the interactions between steroid hormones and neurotransmitters. Various studies had suggested that the estrogen receptor-alpha, one of the proteins that mediates many of the actions of estradiol in the brain, was a nuclear-localized protein. This subcellular localization was consistent with its role as a transcriptional regulator. However, immunocytochemical studies revealed a much wider distribution throughout all parts of some neurons, as illustrated in this photomicrograph. In subsequent studies at the electron microscopic level, we obtained evidence for the presence of estrogen receptors in distal dendrites and axon terminals, as well as in neuronal cell nuclei. These results suggest a variety of possible additional modes of action for estradiol, besides actions mediated by estrogen receptors acting as regulators of transcription.