Effects of ethanol on cultured fetal serotonergic neurons

Molecular pathways in placental-fetal development and disruption

The first trimester of pregnancy ranks high in priority when minimizing harmful exposures, given the wide-ranging types of organogenesis occurring between 4- and 12-weeks' gestation. One way to quantify potential harm to the fetus in the first trimester is to measure a corollary effect on the placenta. Placental biomarkers are widely present in maternal circulation, cord blood, and placental tissue biopsied at birth or at the time of pregnancy termination. Here we evaluate ten diverse pathways involving molecules expressed in the first trimester human placenta based on their relevance to normal fetal development and to the hypothesis of placental-fetal endocrine disruption (perturbation in development that results in abnormal endocrine function in the offspring), namely: human chorionic gonadotropin (hCG), thyroid hormone regulation, peroxisome proliferator activated receptor protein gamma (PPARγ), leptin, transforming growth factor beta, epiregulin, growth differentiation factor 15, small nucleolar RNAs, serotonin, and vitamin D. Some of these are well-established as biomarkers of placental-fetal endocrine disruption, while others are not well studied and were selected based on discovery analyses of the placental transcriptome. A literature search on these biomarkers summarizes evidence of placenta-specific production and regulation of each biomarker, and their role in fetal reproductive tract, brain, and other specific domains of fetal development. In this review, we extend the theory of fetal programming to placental-fetal programming.

Fetal Alcohol Spectrum Disorders: An Overview from the Glia Perspective

Alcohol consumption during pregnancy can produce a variety of central nervous system (CNS) abnormalities in the offspring resulting in a broad spectrum of cognitive and behavioral impairments that constitute the most severe and long-lasting effects observed in fetal alcohol spectrum disorders (FASD). Alcohol-induced abnormalities in glial cells have been suspected of contributing to the adverse effects of alcohol on the developing brain for several years, although much research still needs to be done to causally link the effects of alcohol on specific brain structures and behavior to alterations in glial cell development and function. Damage to radial glia due to prenatal alcohol exposure may underlie observations of abnormal neuronal and glial migration in humans with Fetal Alcohol Syndrome (FAS), as well as primate and rodent models of FAS. A reduction in cell number and altered development has been reported for several glial cell types in animal models of FAS. In utero alcohol exposure can cause microencephaly when alcohol exposure occurs during the brain growth spurt a period characterized by rapid astrocyte proliferation and maturation; since astrocytes are the most abundant cells in the brain, microenchephaly may be caused by reduced astrocyte proliferation or survival, as observed in in vitro and in vivo studies. Delayed oligodendrocyte development and increased oligodendrocyte precursor apoptosis has also been reported in experimental models of FASD, which may be linked to altered myelination/white matter integrity found in FASD children. Children with FAS exhibit hypoplasia of the corpus callosum and anterior commissure, two areas requiring guidance from glial cells and proper maturation of oligodendrocytes. Finally, developmental alcohol exposure disrupts microglial function and induces microglial apoptosis; given the role of microglia in synaptic pruning during brain development, the effects of alcohol on microglia may be involved in the abnormal brain plasticity reported in FASD. The consequences of prenatal alcohol exposure on glial cells, including radial glia and other transient glial structures present in the developing brain, astrocytes, oligodendrocytes and their precursors, and microglia contributes to abnormal neuronal development, reduced neuron survival and disrupted brain architecture and connectivity. This review highlights the CNS structural abnormalities caused by in utero alcohol exposure and outlines which abnormalities are likely mediated by alcohol effects on glial cell development and function.

Prenatal alcohol exposure retards the migration and development of serotonin neurons in fetal C57BL mice

Incomplete neural tube fusion (iNTF), induced by alcohol, in midline floor and roof plates was found in our recent study. In this study, serotonin (5-HT) neurons, known to be born entirely in the midline raphe at brainstem, were examined during their development with fetal alcohol exposure. Weight-matched C57BL mice pregnant dams were divided into three groups on E8: one received ethanol via a chocolate Sustacal liquid diet providing 20% ethanol-derived calories as the sole source of nutrients (ALC); the second received an isocaloric Sustacal liquid diet and was pair-fed to individual dams in the ethanol-fed group (PF); the third was fed ad lib rat chow (Chow). Fetal brains were obtained on E15 and were processed for immunostaining of 5-HT and its trophic factor, S100 beta. The ascending 5-HT neurons, in normal development, appear bilaterally near midline on E12, and by E15, as seen in chow and PF groups, migrate from the midline germinal zone laterally and dorsally to their final position with rich fibers. In contrast, in the E15 ALC group, many 5-HT-im neurons were found remaining in the midline germinal region or had migrated, but with under-differentiated, sparse fibers. There were 20--30% fewer 5-HT-im neurons in ALC as compared to PF and Chow. In addition, the number of S100 beta cells was less in ALC as compared with PF and Chow groups. No difference was found between PF and Chow in number of 5-HT-im or S100 beta-im cells. The 5-HT neurons found compromised in migration and differentiation may, in part, stem from failure of access to floor plate or midline tissue induction and the insufficient support by S100 beta. As 5-HT neurons have been implicated for signaling brain maturation, fewer 5-HT neurons may have lasting effects on the development of brain or, if persistent in the adult, profoundly affect adult brain function.

Deficiency of essential neurotrophic factors in conditioned media produced by ethanol-exposed cortical astrocytes

Prior research in this laboratory has shown that in utero ethanol exposure adversely affects the development of serotonergic neurons. The current study investigated the hypothesis that cortical astrocytes produce trophic factors which are essential for the development of the fetal precursors of serotonergic and other raphe neurons (e.g. rhombencephalic neurons), and that ethanol exposure impairs the production of these factors by astrocytes. The results of these experiments demonstrated that cultured cortical astrocytes produce trophic factors which are necessary for the development of rhombencephalic neurons. Conditioned media obtained from control astrocytes promoted both general neuronal development (increased cell number, cell survival, DNA content, protein content, and neurite outgrowth) and serotonergic neuronal development (increased number of serotonin (5-HT) immunopositive cells and [3H]5-HT uptake). However, the conditioned media produced by ethanol-treated astrocytes (ECM) lacked essential neurotrophic factors. Neuronal cultures maintained in ECM had reduced DNA and neuronal survival, and altered neurite outgrowth. 5-HT immunopositive neurons and [3H]5-HT uptake were also decreased in ECM cultures. Thus, the damaging effects of in utero ethanol exposure on developing serotonergic neurons may be due to impaired production of astroglial neurotrophic factors.

Cortical cell plasma membrane alterations after in vitro alcohol exposure: prevention by GM1 ganglioside

Using choleratoxin/antitoxin immunohistochemistry, this study examined the effects of in vitro alcohol exposure on the morphology of cell plasma membranes in mixed fetal rat cortical cultures, and assessed the neuroprotective effects of exogenous monosialoganglioside (GM1). Gangliosides are involved in critical biological functions, including maintenance of membrane integrity. Plasma membranes are directly affected by alcohol exposure through multiple mechanisms. Results indicate that exposure to alcohol altered plasma membrane morphology as assessed by staining for the surface distribution of membrane GM1. Pretreatment with endogenous GM1 ameliorated the alcohol-induced alterations.

Chronic alcoholics without Wernicke-Korsakoff syndrome or cirrhosis do not lose serotonergic neurons in the dorsal raphe nucleus

Despite the considerable evidence that alcoholics have perturbation of serotonergic function, there is little pathological evidence for alcohol directly affecting the nervous system. The present study aims to assess neuronal loss that occurs as a consequence of alcohol neurotoxicity in the serotonergic dorsal raphe nucleus (DRN). To that end, the brains of eight alcoholics and eight age-matched control cases were carefully screened to eliminate serious liver disease, the sequela of thiamine deficiency, Wernicke-Korsakoff syndrome (WKS), and other pathological abnormalities. Brains were formalin-fixed for 2 weeks, cut, and then immunohistochemically stained using a monoclonal PH8 antibody specific for the rate-limiting enzyme of serotonin synthesis, tryptophan hydroxylase. The morphology of the serotonin-synthesizing neurons and their average size was similar in all cases. However, there was a reduction in the staining intensity of the reaction product in the DRN serotonergic neurons of most alcoholics. Neuronal counts on spaced serial sections revealed that there were an estimated average total of 106,100 +/- 19,500 serotonergic neurons in the DRN of alcoholics and 108,300 +/- 11,800 in the DRN of controls, indicating that in most alcoholics there is no reduction in the number of these neurons. Therefore, the effect of chronic alcohol consumption on the serotonergic system, in the absence of WKS or liver disease, seems to be functional rather than neuropathological.

Effects of ethanol on cultured fetal astroglia

This study investigated the effects of a 4-day ethanol exposure on cultured rhombencephalic astroglia. The contents of astroglial protein and DNA, and astroglial uptake of serotonin (5-HT) were determined. Fetal rhombencephalic astroglia were examined because of this laboratory's evidence that in utero ethanol exposure markedly impairs the development of serotonergic neurons, which are located in this fetal brain area, and because of the recently demonstrated importance of local support glia in neuronal development. The results of these experiments demonstrated that protein was significantly reduced in astroglia cultured in ethanol at either 150 or 300 mg/dl. In addition, these astroglia exhibited decreased [3H]5-HT uptake per well. However, no significant ethanol-associated differences were detected when [3H]5-HT uptake was expressed per mg protein rather than per well. In contrast to the effects of a 4-day ethanol exposure, the acute ethanol exposure did not significantly alter astroglial uptake of [3H]5-HT/well. In addition, the 4-day exposure to 50 to 300 mg/dl of ethanol did not significantly alter astroglial DNA content. In summary, it appears that a 4-day exposure of cultured fetal rhombencephalic astroglia to 150 to 300 mg/dl of ethanol reduces astroglial protein content and astroglial 5-HT uptake. A reduction in total astroglial proteins, potentially including those that act as essential growth factors, could contribute to some of the ethanol-associated alterations in central nervous system development.