Differential sensitivity of cholinergic and GABAergic neurons in chick embryos treated intracerebrally with ethanol at 8 days of embryonic age

Synaptic Plasticity Abnormalities in Fetal Alcohol Spectrum Disorders

The brain's ability to strengthen or weaken synaptic connections is often termed synaptic plasticity. It has been shown to function in brain remodeling following different types of brain damage (e.g., drugs of abuse, alcohol use disorders, neurodegenerative diseases, and inflammatory conditions). Although synaptic plasticity mechanisms have been extensively studied, how neural plasticity can influence neurobehavioral abnormalities in alcohol use disorders (AUDs) is far from being completely understood. Alcohol use during pregnancy and its harmful effects on the developing offspring are major public health, social, and economic challenges. The significant attribute of prenatal alcohol exposure on offspring is damage to the central nervous system (CNS), causing a range of synaptic structural, functional, and behavioral impairments, collectively called fetal alcohol spectrum disorder (FASD). Although the synaptic mechanisms in FASD are limited, emerging evidence suggests that FASD pathogenesis involves altering a set of molecules involved in neurotransmission, myelination, and neuroinflammation. These studies identify several immediate and long-lasting changes using many molecular approaches that are essential for synaptic plasticity and cognitive function. Therefore, they can offer potential synaptic targets for the many neurobehavioral abnormalities observed in FASD. In this review, we discuss the substantial research progress in different aspects of synaptic and molecular changes that can shed light on the mechanism of synaptic dysfunction in FASD. Increasing our understanding of the synaptic changes in FASD will significantly advance our knowledge and could provide a basis for finding novel therapeutic targets and innovative treatment strategies.

The avian embryo as a model for fetal alcohol spectrum disorder

Prenatal alcohol exposure (PAE) remains a leading preventable cause of structural birth defects and permanent neurodevelopmental disability. The chicken (Gallus gallus domesticus) is a powerful embryological research model, and was possibly the first in which the teratogenicity of alcohol was demonstrated. Pharmacologically relevant exposure to alcohol in the range of 20-70 mmol/L (20-80 mg/egg) disrupt the growth of chicken embryos, morphogenesis, and behavior, and the resulting phenotypes strongly parallel those of mammalian models. The avian embryo's direct accessibility has enabled novel insights into the teratogenic mechanisms of alcohol. These include the contribution of IGF1 signaling to growth suppression, the altered flow dynamics that reshape valvuloseptal morphogenesis and mediate its cardiac teratogenicity, and the suppression of Wnt and Shh signals thereby disrupting the migration, expansion, and survival of the neural crest, and underlie its characteristic craniofacial deficits. The genetic diversity within commercial avian strains has enabled the identification of unique loci, such as ribosome biogenesis, that modify vulnerability to alcohol. This venerable research model is equally relevant for the future, as the application of technological advances including CRISPR, optogenetics, and biophotonics to the embryo's ready accessibility creates a unique model in which investigators can manipulate and monitor the embryo in real-time to investigate the effect of alcohol on cell fate.

Supraphysiological acetaldehyde levels suppress growth in chicken embryos

Although exposure to ethanol is known to cause growth inhibition in a developing embryo, the contributing effect of acetaldehyde on growth is not as well documented. In this study, we measured acetaldehyde-induced growth suppression in three different chicken strains: Peterson x Hubbard, HY x Hubbard, and W36 Ginther White Leghorn. The chicken embryo provides a useful model for studying fetal alcohol syndrome (FAS) and has been used extensively in our laboratory. The current study was undertaken to determine whether the chicken embryo could serve as a model for studying the effects of acetaldehyde on growth. Acetaldehyde caused a significant reduction in embryonic weights only at the higher acetaldehyde concentrations. Torso-to-head ratios were unchanged at every acetaldehyde dose for all strains, supporting the suggestion that acetaldehyde-induced growth suppression was generalized in all tissues, rather than being exhibited as a selective decrease of neuronal tissue. All strains experienced a significant decrease in viability only at higher acetaldehyde concentrations, but differences in viability were evident among the strains. These results support findings obtained from previous work done on ethanol-induced differences among chicken strains by supporting the suggestion that the strain of chicken is important when studying the effects of teratogens on growth and viability. More importantly, the supraphysiological concentrations of acetaldehyde necessary to induce growth suppression seem to indicate that the chicken embryo may not be a viable model of FAS for studying the direct effects of acetaldehyde on embryonic growth.

GABA attenuates the neurotoxic effects of ethanol in neuron-enriched cultures from 8-day-old chick embryo cerebral hemispheres

Neuron-enriched cultures were prepared from 8-day-old chick embryo cerebral hemispheres and exposed to ethanol (50 mM), GABA (10(-5) M) and ethanol (50 mM) + GABA (10(-5) M) from day 4 to 8 in culture. At day 8, control, ethanol, GABA and ethanol + GABA-treated cultures were examined morphologically and biochemically. Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities were used as markers for cholinergic and GABAergic neuronal phenotypic expression, respectively. Control cultures showed more numerous and large neuronal aggregates as well as prominent neuritic bundles. Moreover, cultures treated with GABA depicted even more numerous neuronal aggregates with interconnecting neurites as compared to control. In contrast, ethanol-treated cultures exhibited smaller neuronal aggregates with less prominent neuritic bundles than control. However, cultures treated concomitantly with ethanol + GABA exhibited numerous and larger aggregates than cultures treated with ethanol alone. Neuritic bundles which were highly reduced in ethanol-treated cultures became prominent in the presence of GABA. As previously reported, ethanol alone enhanced ChAT and reduced GAD activities. GABA given alone enhanced the expression of both neuronal phenotypes. When GABA was given concomitantly with ethanol the decline in GAD and the rise in ChAT observed in ethanol-treated cultures was restored by GABA to almost control levels. Thus, ethanol-induced alterations in morphology and neuronal phenotypes were counteracted by the neurontrophic effect of GABA.

Early in ovo exposure of chick embryos to ethanol prevents the neuronotrophic effects of intracerebral NGF administration on cholinergic phenotypic expression

We have reported that ethanol administration during early neuroembryogenesis significantly alters neuronal phenotypic expression. In addition, previous findings have indicated that ethanol may interfere with the neurotrophic effects of NGF. In this study, we examined the cholinergic neuronal response to NGF given intracerebrally to embryos at embryonic day 8 (E8) which were exposed to ethanol in ovo via the air sac at E1-3. We found that doses of NGF ranging from 0.01 to 1 ng/2 microliters/embryo given intracerebrally to untreated embryos at E8, and sacrificed at E10, significantly increased choline acetyltransferase (ChAT) activity, the marker for cholinergic neuronal expression. This response was most marked in spinal cord as compared with the low response observed in cerebral hemispheres. In control embryos treated with saline at E1-3 and then receiving NGF intracerebrally at E8, ChAT activity in the spinal cord increased with increasing NGF doses; the highest value was obtained with 0.1 ng NGF. In contrast, in ethanol-treated embryos, ChAT activity was not affected by intracerebral administration of NGF and, in fact, the highest dose (0.1 ng) produced a decrease in ChAT activity. We conclude that: (1) intracerebral administration of NGF produces differential cholinotrophic effects in the embryonic chick CNS; and (2) exposure to ethanol during early neuroembryogenesis interferes with the cholinotrophic effects of NGF.

Ethanol exerts differential effects on high affinity choline uptake in neuron-enriched cultures from 8-day-old chick embryo cerebral hemispheres

Neuronal-enriched cultures were prepared from 8-day-old chick embryo cerebral hemispheres and exposed to ethanol (50 mM) from day 4 to 8 in culture. At day 8, both control and ethanol-treated cultures were processed for [3H]choline uptake in situ. Uptake was performed on cultures containing either Na(+)-plus or Na(+)-free (Li+) HEPES buffer. Total choline uptake as well as Na(+)-dependent and Na(+)-independent choline uptake were calculated. The Km and Vmax were calculated using the Lineweaver-Burke analysis. Our analysis of the data revealed that ethanol-treated cultures exhibited two values for Vmax, one similar to that found in control cultures and one significantly lower than controls. No differences were observed in Km values between control and ethanol-treated cultures. We interpret the low Vmax to represent a population of cholinergic neurons which have been arrested at an immature stage as a result of ethanol insult.