Objectives of the project are as follows: first to identify sexual dimorphisms and the role of gonadal steroids in the regulation of neural and glial signal transduction, proliferation, and survival and in the ontogeny of brain neurotransmitter systems; second, to resolve the mechanisms of both the acute (e.g. enhanced apoptosis) and subacute (e.g. altered neurotransmitter receptor message) neural effects of gonadal steroids; third, to determine the developmental-stage dependent neural consequences of gonadal steroids; and fourth, to identify the subsequent behavioral consequences of perinatal gonadal steroid manipulations. These objectives serve two overall goals: 1) Understanding neuroregulatory mechanisms of gonadal steroids of relevance for affective disorders; and 2) Defining the substrate of differential sensitivity, the process by which the same hormonal stimulus can elicit different responses in different subjects. Findings in the past year include the following: 1) Neurons from E21 female rat ventricular zone and cortical plate show enhanced survival after 14 days compared with those from males, in association with greater expression of MAPK and Akt, but not Bcl-2. These data complement out earlier demonstration that estradiol (E2) preserved neuronal integrity through activation of the PI 3-K/Akt pathway; 2) Sixty minutes culture with 100nM E2 significantly increased the number of cells (neuroblastoma cell line SH-SY5Y) with hyperpolarized mitochondrial membrane potential, effects that were identical to those produced by lithium and that would enhance the actions of cell survival proteins; 3) ERK phosphorylation levels in E21 neurons are increased by a relatively selective ER-beta (estrogen receptor beta) agonist (DPN) in a dose dependent fashion (10 nM-100 nM) but are decreased by an ER-alpha selective agonist (PPT); 4) ER-alpha and PR (progesterone receptor) labelling were observed in pyramidal neurons throughout the layers of the dorsolateral prefrontal cortex of human post-mortem specimens. Expression of PR m-RNA was similar to PR protein, and PR protein was identified as the B isoform. In contrast, the ER identified appeared to be a splice variant of ER alpha. These data suggest that gender and gonadal steroids are significant regulators of cell survival and differentiation in the developing brain, where they undoubtedly play a major role in the formation of gonadal steroid sensitive circuitry. Further, these data help identify additional mechanisms by which gonadal steroids may influence neuronal survival (e.g., effects on mitochondrial regulation of apoptosis) and emphasize the distinct regulatory effects of estradiol acting through alpha or beta receptor subtypes. Finally, the identification of ER and PR in a brain region in humans that mediates both affective and cognitive regulation suggests that both genomic and non-genomic effects of gonadal steroids may contribute to expression of symptoms in patients with affective disorders.
