The long-term goal of the proposed research is to determine the molecular mechanisms by which ethanol produces teratogenic effects on the central nervous system. Specific features of ethanol-induced CNS damage are remarkably consistent among clinical and animal studies, suggesting a common underlying mechanism(s) for these defects. A common characteristic of the damage observed in ethanol-exposed brains is neuronal agenesis and defects in cell migration. Several kinds of studies indicate that at least a subset of ethanol-induced CNS damage may be due to ethanol effects on thyroid hormone function. Independently, studies have indicated that ethanol effects on CNS development may be mediated by blocking the de novo synthesis of retinoic acid. Considering that thyroid hormone receptors are ligand-dependent transcription factors that are known to form functional heterodimers with receptors for retinoic acid, the working hypothesis is that ethanol interferes with the interaction of these two signalling systems at precise times during CNS development. This hypothesis forms the basis for the prediction that brain areas which express both thyroid hormone receptors and receptors for retinoic acid are those that are the most sensitive to the deleterious effects of prenatal ethanol exposure. The first specific aim of the proposed work is to determine whether these receptors are co-expressed by neurons of the cortex and hippocampus during the developmental periods they are known to be sensitive to the deleterious effects of ethanol. To accomplish this, we will use a sensitive dual-label in situ hybridization procedure. Next, we will determine whether alcohol exposure can affect the expression of these receptors in cortex and hippocampus. We will use a model of acute ethanol administration to pregnant females so that we can determine the temporal relationship between the effect of ethanol on CNS damage and alterations in the expression of TRs and RAR/RXRs within known windows of vulnerability to the deleterious effects of ethanol. We will evaluate three doses of ethanol and will control for possible nutritional effects using a """"""""pair-feeding"""""""" paradigm and for possible stress effects by including an untreated group. In addition, we will confirm our findings using a chronic ethanol treatment model for which substantial information exists concerning cortical development. We will also confirm that ethanol effects on expression of TR and RAR/RXR mRNAS affect thyroid hormone and retinoic binding. Finally, we will also determine whether T3 and/or RA can ameliorate the effects of ethanol on CNS damage and on TR and RAR/RXR expression. The proposed experiments will potentially identify a mechanism of FAS. The results could explain why clinical and experimental FAS brains exhibit neuronal agenesis and defective neuronal migration. and why there are windows of vulnerability to the deleterious effects of ethanol. These studies will also leave clear implications to problems of FAS, and these issues can be effectively explored based on the initial, proposed studies.
