Fetal alcohol exposure in C57BL mice has been found to produce incomplete neural tube closure (iNTC). These iNTCs occur intermittently along the neural axis. The iNTC is hypothesized to reflect and contribute to developmental defects in midline brain structures. It is futher hypothesized that abnormal development of midline structures derails brain developmental cascades regulated in part by serotonin (5-HT), including cortical development. The first three aims will be tested in inbred C57BL mice using a liquid diet, for which preliminary data already demonstrate significant embryonic midline defects.
Aim 1, on developing, and Aim 2 on adult brains will extend our preliminary evidence of alcohol-induced iNTC by investigating the time course of closure of the neural tube.
These aims will also involve quantitative morphometric analysis of associated midline structures such as the septum, subcommissural organ, median eminence, ventricles, and midline brainstem. A key midline structure, the raphe, will be the focus of a detailed developmental study. At the time of neural tube closure, the raphe contains germinal cells for 5-HT.
A specific aim of this proposal is to assess whether iNTC in this region is associated with defects in the development of 5-HT neurons. The first 2 aims will characterize the abnormal development of 5-HT neurons from the embryonic stage (E13) to maturity (P45). The first 2 aims will also evaluate alcohol-induced structural abnormalities in forebrain and cortical development, since it is regulated in part by trophic influences of 5-HT innervation early in cortical plate formation. 5-HT has been implicated in signaling cortical maturation and somatosensory barrel formation. In addition to the well-established direct influence of fetal alcohol exposure on cortical neurogenesis, there may be an interactive effect through defective 5-HT innervation of the cortex. The development of the frontal and somatosensory barrel formation will be evaluated quantitatively using measures of size, neuronal number, and extent of 5-HT innervation.
Aim 3 tests the hypothesis that pharmacological stimulation of 5-HT1A receptors during the prenatal alcohol treatment can protect against midline 5-HT deficits and ameliorate the resulting abnormal developmental cascade of cortical structural defects.
In Aim 4, a test of generality of iNTC and 5-HT defects will be performed by comparing alcohol effects in C57BL mice with effects in a heterogeneous stock using intragastric intubation. The results of the proposed studies will provide direct evidence of the sequelae of alcohol-induced embryonic structural abnormalities of the 5-HT system, and will test the potential to prevent the cascading developmental brain defects by pharmacological interventions.
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