The goal of this project is to develop and validate an in vitro organotypic primate model system for studying neural plasticity, and to initiate experiments that will clarify the cellular and molecular events underlying hormonal control of neural development in the cerebral cortex of the primate. Both steroid and thyroid hormones influence cognitive abilities and appear to exert profound effects on the structure and neurochemistry of the cortex. Moreover, there are significant differences between the organization and neurochemistry of the cerebral cortex in primates and other mammalian animal models. Thus, it is likely that unique mechanisms participate in regulating cortical development in humans and nonhuman primates. During the past project period, we processed a total of 6 fetuses and prepared over 500 explant cultures. Nearly all of these proved to be viable, and most appeared to remain healthy for at least 30 days in vitro. These cultures showed organotypic patterns of lamination characteristic of developing cortex in vivo and numerous neurons were immunoreactive for glutamate receptors. The presence of interlaminar connections was confirmed by making small implants of the fluorescent tracer DiI into localized regions of the cortical explants. Retrogradely labeled cells occupied positions that corresponded to cell layers, and labeled projection axons passed laterally in the explant through discrete zones as they do in mature tissue. In addition, the morphology of individual neurons appeared to be quite complex and generally was consistent with published reports. We have used this new model system to begin to study the role of sex steroid and thyroid hormones on cortical development. Our initial results suggest that estradiol promotes neurite outgrowth from cortical explants, which was not observed with testosterone. In preparation for an evaluation of the effects of sex steroids on neuronal function, we prepared cultures of primate cortex on glass coverslips using the roller-tube"""""""" culture method and used calcium imaging techniques to assess neuronal responsiveness to glutamate in these cultures. Neurons in the explants showed dose dependant changes in internal calcium concentrations in response to glutamate challenge. Future studies will exploit this novel experimental model system to further characterize hormone and neurotransmitter expression, as well as study hormonal regulation of neuronal signal transduction under defined, pharmacologically controlled conditions.
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