The effects of ethanol on a fetus are extensive, devastating, and often permanent. Depending upon the population, ethanol affects as many as 2% of all live births. The most profound effects are on the nervous system. Gestational ethanol exposure causes structural changes in many regions of the brain. The permanent effects of ethanol include (a) a reduction in the number of neurons in the mature brain, (b) aberrant connections formed by surviving neurons, and (c) depression of brain metabolism. Ultimately, these changes manifest as mental retardation and/or alterations in behavior. One region of the brain that appears refractory to ethanol is the ventrobasal nucleus of the thalamus (VB). Not only does exposure to ethanol not affect the final number of neurons, metabolism in this region is also unaltered. The VB is unique in that it includes a period of in situ proliferation in the early postnatal period. A concurrent event is the arrival of corticothalamic afferents, thus, the postnatal neurogenesis in the VB may be important for matching neuronal number in the VB with that in somatosensory cortex. The goal of the present study is to understand the apparent protection this region has against the deleterious effects of prenatal exposure to ethanol. We will test the hypotheses (1) that postnatal neurogenesis in the ventrobasal nucleus of the thalamus (VB) is part of a matching between of connections between the VB and the somatosensory cortex that relies on neurotrophins, and (2) that the apparent refractoriness of the VB results from ethanol-induced changes in postnatal neuronogenesis and neuronal survival, and that neurotrophins play a role in these developmental phenomena. The proposed project consists of two complementary studies. (1) The role of neurotrophins in postnatal proliferation of cells in the VB, and the effect of prenatal exposure to ethanol on the neurotrophin system will be determined. These experiments will utilize the powerful organotypic slice method in which at least a portion of the normal brain connectivity is maintained while allowing manipulation of growth factor concentration. (2) The mechanism of action of the neurotrophins in the developing trigeminal-somatosensory system will be determined. Initial experiments examine the localization of neurotrophin mRNA within the trigeminal-somatosensory system. Subsequent experiments will manipulate neurotrophins and determine (a) the effect of ethanol on the cycling population and (b) the roles of the two distinct mechanisms by which neurotrophins act, long-distance (anterograde/retrograde) communication or local (autocrine/paracrine) processing. In summary, the effect of prenatal exposure to ethanol on the postnatal development of the VB provides (1) an ideal tool to appreciate CNS development, (2) insight into mechanisms underlying neurotrophin-mediated cell proliferation, and (3) further understanding of the neurotoxic effects of ethanol and the etiology of fetal alcohol spectrum disorder (FASD).
The experiments we propose examine the effect of a common environmental teratogen, alcohol, on brain development, specifically on a population of cells that behave in a stem cell-like manner and appear relatively unaffected by exposure to alcohol. Understanding the characteristics of these cells may provide some insight into how some cell populations are affected by alcohol but others are resistant. Eventually such knowledge may be of use in protecting fetuses from alcohol-induced damage.
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