Morphological alteration in rat hippocampal neuronal dendrites following chronic binge prenatal alcohol exposure
Introduction
Prenatal alcohol exposure (PAE) is a leading cause of Fetal Alcohol Spectrum Disorders (FASD), which is described as an array of cognitive, neurobehavioral and physical developmental disabilities (Riley and McGee, 2005, Sokol et al., 2003, Riley et al., 2011). A recent study reported that 1 in 10 pregnant women consumed alcohol in the past month and that 1 in 33 women binge drank during pregnancy (Tan et al., 2015), with 8.4% of newborns exhibiting biochemical evidence of PAE (Bakhireva et al., 2017). The prevalence of FASD is estimated at 2–5% of school-age children in the United States (May et al., 2018, Roozen et al., 2016). PAE-induced developmental deficits can be severe and may persist for a lifetime.
The hippocampus is intricately associated with cognition, behavior, learning and memory. The developing hippocampus is profoundly vulnerable to the teratogenic effects of alcohol (Lebel et al., 2011, Archibald et al., 2001, Gautam et al., 2015). The susceptibility of the hippocampus may vary depending on the dose, duration, timing, and pattern of alcohol exposure. (Ho et al., 1972, Gil-Mohapel et al., 2010, Dudek et al., 2014, Kodituwakku, 2007, Savage et al., 2002). Alcohol exposure during hippocampal development has been shown to alter hippocampal synaptic plasticity (Bhattacharya et al., 2015, Sutherland et al., 1997, Medina, 2011, Fontaine et al., 2016), synaptic activity (Kajimoto et al., 2016, Krawczyk et al., 2016), cellular morphology (Berman and Hannigan, 2000, Ramos et al., 2002), and gene expression (Chen et al., 2013, Chater-Diehl et al., 2016).
Although the hippocampus has been recognized as a vulnerable target of alcohol-induced developmental damage, there is little knowledge related to the morphological alteration of the hippocampal neurons caused by alcohol exposure in vivo, mainly in adults and in neonates (Barnes and Walker, 1981, McMullen et al., 1984, Goeke et al., 2018). Furthermore, the effect of prenatal exposure to alcohol on morphological alteration in the hippocampal fields and the dentate gyrus remains largely unknown in the context of FASD. We recently identified using proteomics and RNA-SEQ that the developing hippocampus is a major target of alcohol exposure in utero (Davis-Anderson et al., 2018, Lunde-Young et al., 2019). Following these high throughput studies, we also recently reported major deficits in hippocampal mTOR signaling, a pathway closely associated with hippocampal neuronal development (Lee et al., 2020). As a logical next step, we herein hypothesized that chronic binge alcohol exposure during pregnancy alters developmental dendritic morphological adaptations. In the present study, utilizing Golgi-Cox staining-based morphological analyses, we evaluated dendrite arborization in the postnatal day 10 (PND) rat hippocampal formation CA1 field, CA2/3 field, and the dentate gyrus (DG) neurons following alcohol exposure in utero.
Section snippets
Prenatal exposure to alcohol increases dendritic complexity of CA1 neurons
Neuronal tracer was applied to visualize the overall dendritic branches of the CA1 neurons (Fig. 1A), and Sholl analysis was utilized to localize the effect of PAE. As shown in Fig. 1B, a significant change in the number of intersections of CA1 neurons were localized at 10–50 µm of the dendrite process from the center of soma (Fig. 1B; F(1, 5) = 19.57, P = 0.0069) in the Alcohol group compared to those in the PF-Cont group. The Alcohol group showed significantly higher number of primary
Discussion
To our knowledge, this is the first study investigating morphological alterations related to dendritic arborization throughout the postnatal rat hippocampal formation, utilizing Golgi-cox staining and neuronal tracing following chronic binge prenatal alcohol exposure. We herein demonstrate that chronic binge prenatal alcohol exposure during pregnancy significantly increased the complexity of dendritic arborization in the hippocampal formation.
Mechanistic perspectives and conclusions
We recently reported that gestational chronic binge alcohol exposure altered hippocampal transcriptome (Lunde-Young et al., 2019), proteome (Davis-Anderson et al., 2018), and signaling pathways, including the mammalian target of rapamycin (mTOR) pathway following first two trimester-equivalent alcohol exposure (Lee et al., 2020). Since mTOR plays a crucial role in regulating protein synthesis in response to synaptic formation and plasticity, abnormalities in mTOR activity may be associated with
Animals
All experimental procedures were in accordance with National Institutes of Health guidelines (NIH Publication No. 85–23, revised 1996) and approved by the Institutional Animal Care and Use Committee at Texas A&M University. Experimental procedures and the prenatal alcohol exposure paradigm were conducted as described previously (Naik et al., 2016, Davis-Anderson et al., 2018, Lunde-Young et al., 2019, Lee et al., 2020, Naik et al., 2020). Briefly, timed-pregnant Sprague Dawley rats purchased
CRediT authorship contribution statement
Jehoon Lee: Formal analysis, Investigation, Methodology, Visualization, Writing - original draft, Writing - review & editing. Vishal Naik: Investigation, Visualization, Writing - review & editing. Marcus Orzabal: Investigation, Writing - review & editing. Raine Lunde-Young: Investigation. Jayanth Ramadoss: Conceptualization, Funding acquisition, Project administration, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This study was supported by National Institutes of Health [AA19446, AA23520, AA23035, HL151497]; Texas A&M University [Tier One Program]; and Texas A&M Presidential Transformational teaching Grant (JR).
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