P6: Astroglial diversity in rat dopaminergic nuclei: implications for selective neuronal degeneration and Parkinson's disease

Loss of dopaminergic (DA) neurons of the ventral midbrain are implicated in Parkinson's disease (PD), while those of the hypothalamus (HY) are relatively spared in this disease. The contribution of astroglia to this disease process has yet to be elucidated. This study set out to compare the midbrain and HY nuclei in terms of astroglial diversity and selective DA neuronal degeneration. In order to do this the numbers and phenotypes of the astroglia surrounding midbrain DA neurons will be compared with those in the HY. The first aim was to compare the astroglial composition of embryonic rat ventral mesencephalic (VM) and embryonic rat hypothalamic (HY) cultures. Before doing so it was necessary to ascertain the embryonic age of tissue which yields the greatest amount of DA neurons from HY cultures. This was done by growing cultures from E15, E16, E17, and E18 HY and staining them immunocytochemically for GFAP (an astroglial marker), β-tubulin (a neuronal marker) and TH (a DA neuronal marker). This study found that the highest yield of DA neurons after 6 days in vitro was achieved from E15 HY tissue. Cultures prepared from E15 HY were then compared to cultures prepared from E14 VM (previously shown to give the highest yield of DA neurons) in terms of cellular composition. The next part of this study involved comparing the GFAP and TH positive cells in the substantia nigra to the arcuate nucleus and the zona incerta (DA nuclei of the HY) in adult rat brain. Cell types were identified using immunohistochemistry on cryosections and numbers of each were calculated using the optical disector method. The results of this study will give valuable information on the profile of glial cells surrounding dopaminergic neurons in the SN, which degenerates in PD and the hypothalamic nuclei which are spared in this disease.