Ethanol Exposure During Pregnancy Persistently Attenuates Cranially Directed Blood Flow in the Developing Fetus: Evidence from Ultrasound Imaging in a Murine Second Trimester Equivalent Model

Ethanol consumption during pregnancy can lead to brain, craniofacial, cardiovascular and limb defects that are collectively termed Fetal Alcohol Spectrum Disorders (FASD) (Abel, 1984; Jones et al., 1973). FASD is a leading non-genetic cause of mental retardation (Abel, 1995). Significant numbers of pregnant women continue to consume ethanol into the second trimester (SAMHSA, 2009), a critical period for fetal neurogenesis and brain angiogenesis. FASD continues to be a significant public health problem, with an estimated incidence of 2–5% of the US population (May et al., 2009). Significant research has focused on the fetal neural basis for the emergence of behavioral deficits associated with maternal ethanol exposure. These studies showed that ethanol directly interferes with several aspects of neural development, including the biology of neural stem cells (Camarillo and Miranda, 2008; Santillano et al., 2005; Vangipuram et al., 2008), neuronal migration (reviewed in (Bearer, 2001)), and the survival and maturation of differentiating neurons (reviewed in (Goodlett and Horn, 2001)). By promoting death (West et al., 2001) and disrupting synaptic connectivity (Carta et al., 2006) of cerebellar neurons for example, ethanol may promote the appearance behavioral deficits like gait disturbances. However, ethanol’s neural effects could additionally be mediated by disturbances within non-neural tissue including developing brain vasculature (Parnell et al., 2007). During the second trimester period, a network of blood vessels within the sub-arachnoid space give rise to microvessels that invade the fetal brain (Norman and O’Kusky, 1986) during the same time period that neural stem cells generate most of the neurons of the brain. This emergent vasculature supports nutrition needs and endocrine control of fetal growth (Fowden and Forhead, 2009) and promotes neural development (Tam and Watts, 2010). Previous research showed that ethanol exposure during the murine first trimester-equivalent period produced a persistent alteration in cardiac physiology (Serrano et al., 2010), which persisted into the critical second trimester window for brain development. In ovine models, chronic fetal ethanol exposure can increase cerebral blood flow under acidaemic and hypercapnic conditions (Parnell et al., 2007) and second trimester exposure alters subsequent cerebral vascular responses to hypoxia and to vasodilatory hormones like VIP (Mayock et al., 2007; Ngai et al., 2008). However, until recently it has been technically difficult to visualize fetal blood flow, particularly in smaller arteries. Modern high-resolution ultrasonography makes possible repeated, non-invasive and real-time analysis of blood flow in sub-millimeter sized vessels like the murine fetal middle cerebral arteries, making it feasible to ask questions about the direct impact of adverse environmental factors like maternal ethanol consumption on fetal cerebral blood flow. In this study, we used this technology to test the hypothesis that single as well as repeated binge-like episodes of maternal ethanol exposure, which are particularly damaging to the fetus (Maier and West, 2001), both immediately and persistently alter cranially-directed fetal blood flow during a period which encompasses blood vessel and neuron formation in the developing brain.