Prenatal ethanol exposure can cause the Fetal Alcohol Syndrome, which is characterized by, among other symptoms, microencephaly and mental retardation. Ethanol exposure can reduce neuronal numbers in several brain areas during development, with the cerebellum being one of the most sensitive regions, in which Purkinje and granule neurons are lost. The neuronal loss results, at least in part, from direct effects of ethanol on neuronal survival, but the mechanism of ethanol's action is not known. During development, neurons are subject to apoptosis, a form of programmed cell death that has been attributed to a loss of trophic support. Cells undergoing apoptotic death display characteristic morphological and biochemical changes which distinguish them from cells undergoing necrotic death. Necrotic death can often be equated with excitotxicity, which results from overstimulation of the cells by the excitatory amino acid neurotransmitter, glutamate, acting at the N-methyl-D-aspartate (NMDA) receptor. Ethanol has been shown to modulate apoptosis in certain neuronal populations, and ethanol can also affect necrotic cell death by altering the properties of NMDA receptors. Cerebellar granule neurons, which are lost as a result of in vivo ethanol exposure during development, provide an excellent model in which to study the mechanism by which ethanol affects apoptosis and necrosis during development. In primary culture, these cells undergo apoptotic death in the absence of depolarization, and their survival is promoted by exposure to depolarizing concentrations of K+ or to NMDA, which are thought to mimic the innervation of granule cells by glutamatergic mossy fibers in vivo. Initial results suggest that ethanol reduces the trophic effect of NMDA in these cells, i.e., increases apoptosis. We hypothesize that the ability of ethanol to inhibit NMDA receptor function in the cerebellar granule cells leads to this enhanced apoptotic death. We will characterize the acute and chronic effects of ethanol on NMDA receptor characteristics and function (measured as increases in intracellular CA2+) and on apoptosis (measured with cell morphology, DNA fragmentation, fluorescein flororescence and the ApopTag method), as well as necrosis, in cerebellar granule cells during their development in vitro. We will also evaluate the role of the cyclic AMP system, which has been reported to inhibit apoptosis in cerebellar granule cells, in the trophic effect of NMDA, by measuring NMDA-stimulated cyclic AMP production in the presence and absence of ethanol, and attempting to influence the trophic effect of NMDA with protein kinase A modulators. Understanding the mechanism of ethanol's effects on neuronal death during development may lead to therapies to ameliorate this damage.
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