Effects of ethanol on the inner layers of chick retina during development

Assessing CaMPARI as new approach methodology for evaluating neurotoxicity

Developmental exposure to environmental toxicants has been linked to the onset of neurological disorders and diseases. Despite substantial advances in the field of neurotoxicology, there remain significant knowledge gaps in our understanding of cellular targets and molecular mechanisms that mediate the neurotoxicological endpoints associated with exposure to both legacy contaminants and emerging contaminants of concern. Zebrafish are a powerful neurotoxicological model given their high degree sequence conservation with humans and the similarities they share with mammals in micro- and macro-level brain structures. Many zebrafish studies have effectively utilized behavioral assays to predict the neurotoxic potential of different compounds, but behavioral phenotypes are rarely able to predict the brain structures, cell types, or mechanisms affected by chemical exposures. Calcium-modulated photoactivatable ratiometric integrator (CaMPARI), a recently developed genetically-encoded calcium indicator, undergoes a permanent green to red switch in the presence of elevated intracellular Ca2+ concentrations and 405-nm light, which allows for a "snapshot" of brain activity in freely-swimming larvae. To determine whether behavioral results are predictive of patterns of neuronal activity, we assessed the effects of three common neurotoxicants, ethanol, 2,2',3,5',6-pentachlorobiphenyl (PCB 95), and monoethylhexyl phthalate (MEHP), on both brain activity and behavior by combining the behavioral light/dark assay with CaMPARI imaging. We demonstrate that brain activity profiles and behavioral phenotypes are not always concordant and, therefore, behavior alone is not sufficient to understand how toxicant exposure affects neural development and network dynamics. We conclude that pairing behavioral assays with functional neuroimaging tools such as CaMPARI provides a more comprehensive understanding of the neurotoxic endpoints of compounds while still offering a relatively high throughput approach to toxicity testing.

Human Retinal Organoids Provide a Suitable Tool for Toxicological Investigations: A Comprehensive Validation Using Drugs and Compounds Affecting the Retina

Retinal drug toxicity screening is essential for the development of safe treatment strategies for a large number of diseases. To this end, retinal organoids derived from human pluripotent stem cells (hPSCs) provide a suitable screening platform due to their similarity to the human retina and the ease of generation in large-scale formats. In this study, two hPSC cell lines were differentiated to retinal organoids, which comprised all key retinal cell types in multiple nuclear and synaptic layers. Single-cell RNA-Seq of retinal organoids indicated the maintenance of retinal ganglion cells and development of bipolar cells: both cell types segregated into several subtypes. Ketorolac, digoxin, thioridazine, sildenafil, ethanol, and methanol were selected as key compounds to screen on retinal organoids because of their well-known retinal toxicity profile described in the literature. Exposure of the hPSC-derived retinal organoids to digoxin, thioridazine, and sildenafil resulted in photoreceptor cell death, while digoxin and thioridazine additionally affected all other cell types, including Müller glia cells. All drug treatments caused activation of astrocytes, indicated by dendrites sprouting into neuroepithelium. The ability to respond to light was preserved in organoids although the number of responsive retinal ganglion cells decreased after drug exposure. These data indicate similar drug effects in organoids to those reported in in vivo models and/or in humans, thus providing the first robust experimental evidence of their suitability for toxicological studies.

Embryonic ethanol exposure on zebrafish early development

INTRODUCTION

Embryonic exposure to ethanol leads to a condition of physical, behavioral, and cognitive deficiencies named fetal alcohol spectrum disorders (FASD). The most severe variations are in fetal alcohol syndrome (FAS), which is easier to diagnose and not studied in animal models. On the other side, the pFAS (partial fetal alcohol syndrome) includes cases of alcohol-related congenital disabilities and neurodevelopmental disorder with an inconclusive diagnosis. In recent years, the zebrafish has become a valuable model to study FASD and its variations.

METHODS

This study characterizes the zebrafish embryonic and larval development after low and moderate ethanol concentration exposure. Fish eggs were exposed to 0.0%, 0.25%, 0.5%, and 1.0% ethanol at 24 hr postfertilization, and embryonic development was observed every 8 hr up to 120 hpf. It evaluated movements, phenotypic abnormalities, hatching, cardiac function and heartbeat frequency, larvae length at 120 hpf, and the apoptotic cells' fluorescence stained with acridine orange.

RESULTS

Embryonic exposure to 0.5% and 1% ethanol presented reduced body size, decreased heartbeat rate, higher numbers of apoptotic cells, and hatching time differences.

CONCLUSIONS

Our results suggest any ethanol exposure during embryogenesis can be harmful and reinforces zebrafish as a suitable model for fetal alcohol spectrum disorders (FASD).

Retinal structure and function in monkeys with fetal alcohol exposure

Exposure to ethanol in utero leads to several brain development disorders including retinal abnormalities whose underlying cellular pathogenesis remains elusive. We recently reported that fetal alcohol exposure (FAE) in vervet monkeys induces anomalies of full-field electroretinogram (ERG) waveforms that suggest premature aging of the retina. The goal of this study is to characterize the anatomo-functional mechanisms underlying the retinal changes observed in fetal alcohol exposed (FAE) monkeys, and age- and sex-matched normals. First, we examined in vivo the fundus of the eyes, measured intraocular pressure (IOP) and assessed cone activity using flicker ERG. Second, we investigated ex vivo, protein expression and anatomical organization of the retina using Western blotting, classical histology and immunohistochemistry. Our results indicated that the fundus of the eyes showed both, increased vascularization (tessellated fundus) and IOP in FAE monkeys. Furthermore, light-adapted flicker responses above 15 Hz were also significantly higher in FAE monkeys. Although there were no obvious changes in the overall anatomy in the FAE retina, Glial Fibrillary Acidic Protein (GFAP, a potent marker of astrocytes) immunoreactivity was increased in the FAE retinal ganglion cell layer indicating a strong astrogliosis. These alterations were present in juvenile (2 years old) monkeys and persist in adults (8 years old). Moreover, using specific cell type markers, no significant modifications in the morphology of the photoreceptors, horizontal cells, bipolar cells, and amacrine cells were observed. Our data indicate that FAE does indeed induce anatomical changes within the retinal ganglion cell layer that are reflected in the increased photosensitivity of the cone photoreceptors.

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.

Embryonic alcohol exposure promotes long-term effects on cerebral glutamate transport of adult zebrafish

Ethanol is a widely consumed substance throughout the world. During development it can substantially damage the human fetus, whereas the developing brain is particularly vulnerable. The brain damage induced by prenatal alcohol exposure may lead to a variety of long-lasting behavioral and neurochemical problems. However, there are no data concerning the effects of developmental ethanol exposure on the glutamatergic system, where extracellular glutamate acts as signaling molecule. Here we investigated the effect of ethanol exposure for 2h (concentrations of 0.0%, 0.1%, 0.25%, 0.50%, and 1.00%) in embryos at 24h post-fertilization (hpf) by measuring the functionality of glutamate transporters in the brain of adult (4 months) zebrafish. However, ethanol 0.1%, 0.25% and 0.50% decreased transport of glutamate to 81.96%, 60.65% and 45.91% respectively, when compared with the control group. Interestingly, 1.00% was able to inhibit the transport activity to 68.85%. In response to the embryonic alcohol exposure, we found impairment in the function of cerebral glutamate transport in adult fish, contributing to long-term alteration in the homeostasis glutamatergic signaling.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.

Ethanol affects the development of sensory hair cells in larval zebrafish (Danio rerio)

Children born to mothers with substantial alcohol consumption during pregnancy can present a number of morphological, cognitive, and sensory abnormalities, including hearing deficits, collectively known as fetal alcohol syndrome (FAS). The goal of this study was to determine if the zebrafish lateral line could be used to study sensory hair cell abnormalities caused by exposure to ethanol during embryogenesis. Some lateral line sensory hair cells are present at 2 days post-fertilization (dpf) and are functional by 5 dpf. Zebrafish embryos were raised in fish water supplemented with varying concentrations of ethanol (0.75%-1.75% by volume) from 2 dpf through 5 dpf. Ethanol treatment during development resulted in many physical abnormalities characteristic of FAS in humans. Also, the number of sensory hair cells decreased as the concentration of ethanol increased in a dose-dependent manner. The dye FM 1-43FX was used to detect the presence of functional mechanotransduction channels. The percentage of FM 1-43-labeled hair cells decreased as the concentration of ethanol increased. Methanol treatment did not affect the development of hair cells. The cell cycle markers proliferating cell nuclear antigen (PCNA) and bromodeoxyuridine (BrdU) demonstrated that ethanol reduced the number of sensory hair cells, as a consequence of decreased cellular proliferation. There was also a significant increase in the rate of apoptosis, as determined by TUNEL-labeling, in neuromasts following ethanol treatment during larval development. Therefore, zebrafish are a useful animal model to study the effects of hair cell developmental disorders associated with FAS.

Effects of early postnatal alcohol exposure on the developing retinogeniculate projections in C57BL/6 mice

Previous studies on the adverse effects of perinatal exposure to ethanol (EtOH) on the developing visual system mainly focused on retinal and optic nerve morphology. The aim of the present study was to investigate whether earlier reported retinal and optic nerve changes are accompanied by anomalies in eye-specific fiber segregation in the dorsal lateral geniculate nucleus (dLGN). C57BL/6 mice pups were exposed to ethanol by intragastric intubation at either 3 or 4 g/kg from postnatal days (PD) 3-10, the third trimester equivalent to human gestation. Control (C) and intubation control (IC) groups not exposed to ethanol were included. On PD9, retinogeniculate projections were labeled by intraocular microinjections of cholera toxin-β (CTB) either conjugated to Alexa 488 (green) or 594 (red) administrated to the left and right eye, respectively. Pups were sacrificed 24 h after the last CTB injection. The results showed that ethanol exposure decreased the total number of dLGN neurons and significantly reduced the total dLGN projection as well as the contralateral and ipsilateral projection areas.

Effects of early postnatal exposure to ethanol on retinal ganglion cell morphology and numbers of neurons in the dorsolateral geniculate in mice

BACKGROUND

The adverse effects of fetal and early postnatal ethanol intoxication on peripheral organs and the central nervous system are well documented. Ocular defects have also been reported in about 90% of children with fetal alcohol syndrome, including microphthalmia, loss of neurons in the retinal ganglion cell (RGC) layer, optic nerve hypoplasia, and dysmyelination. However, little is known about perinatal ethanol effects on retinal cell morphology. Examination of the potential toxic effects of alcohol on the neuron architecture is important because the changes in dendritic geometry and synapse distribution directly affect the organization and functions of neural circuits. Thus, in the present study, estimations of the numbers of neurons in the ganglion cell layer and dorsolateral geniculate nucleus (dLGN), and a detailed analysis of RGC morphology were carried out in transgenic mice exposed to ethanol during the early postnatal period.

METHODS

The study was carried out in male and female transgenic mice expressing yellow fluorescent protein (YFP) controlled by a Thy-1 (thymus cell antigen 1) regulator on a C57 background. Ethanol (3 g/kg/d) was administered to mouse pups by intragastric intubation throughout postnatal days (PDs) 3 to 20. Intubation control (IC) and untreated control (C) groups were included. Blood alcohol concentration was measured in separate groups of pups on PDs 3, 10, and 20 at 4 different time points, 1, 1.5, 2, and 3 hours after the second intubation. Numbers of neurons in the ganglion cell layer and in the dLGN were quantified on PD20 using unbiased stereological procedures. RGC morphology was imaged by confocal microscopy and analyzed using Neurolucida software.

RESULTS

Binge-like ethanol exposure in mice during the early postnatal period from PDs 3 to 20 altered RGC morphology and resulted in a significant decrease in the numbers of neurons in the ganglion cell layer and in the dLGN. In the alcohol exposure group, out of 13 morphological parameters examined in RGCs, soma area was significantly reduced and dendritic tortuosity significantly increased. After neonatal exposure to ethanol, a decrease in total dendritic field area and an increase in the mean branch angle were also observed. Interestingly, RGC dendrite elongation and a decrease in the spine density were observed in the IC group, as compared to both ethanol-exposed and pure control subjects. There were no significant effects of alcohol exposure on total retinal area.

CONCLUSIONS

Early postnatal ethanol exposure affects development of the visual system, reducing the numbers of neurons in the ganglion cell layer and in the dLGN, and altering RGCs' morphology.

Ethanol-induced microphthalmia is not mediated by changes in retinoic acid or sonic hedgehog signaling during retinal neurogenesis

BACKGROUND

Microphthalmia (reduced eye size), generally accompanied by vision defects, is a hallmark of fetal alcohol spectrum disorder (FASD) in humans. In zebrafish, embryonic ethanol exposure over the time of retinal neurogenesis also results in microphthalmia. This microphthalmia is in part the consequence of reduced retinal cell differentiation, including photoreceptors. Here we pursue 2 signaling pathways implicated in other aspects of FASD pathogenesis: retinoic acid (RA) and Sonic hedgehog (Shh).

METHODS

We evaluated markers for RA and Shh signaling within the eyes of embryos treated with ethanol during the period of retinal neurogenesis. We also performed rescue experiments using administration of exogenous RA and microinjection of cholesterol, which augments Shh signaling.

RESULTS

Using sequential or co-treatments, RA did not rescue ethanol-induced microphthalmia at any concentration tested. In addition, RA itself caused microphthalmia, although the underlying mechanisms were distinct from those of ethanol. Interestingly, RA treatment appeared to recover photoreceptor differentiation in a concentration-dependent manner. This may be an independent effect of exogenous RA, as ethanol treatment alone did not alter RA signaling in the eye. Cholesterol injection also did not rescue ethanol-induced microphthalmia at any concentration tested, and ethanol treatments did not alter expression of shh, or of ptc-2, which is normally regulated by Shh signaling.

CONCLUSIONS

Together these findings indicate that, during the time of retinal neurogenesis, effects of ethanol on eye development are likely independent of the RA and Shh signaling pathways. These studies suggest that FASD intervention strategies based upon augmentation of RA or Shh signaling may not prevent ethanol-induced microphthalmia.

Ocular deficits associated with alcohol exposure during zebrafish development

Approximately 90% of fetal alcohol syndrome cases are accompanied by ocular abnormalities. The zebrafish (Danio rerio) is a well-known developmental model that provides an opportunity for better understanding the histological and cytological effects of developmental exposure to ethanol on the vertebrate eye. The purpose of the present study was to determine the gross, microscopic, and ultrastructual effects of developmental exposure to ethanol in the zebrafish model. Eggs were obtained from WT outbred zebrafish and exposed to 0%, 0.1%, 0.2%, 0.4%, 0.5%, or 1.0% (v/v) ethanol to assess viability and the effect of dose and duration of exposure on eye size. Light and electron microscopy were performed on ethanol-treated and control larvae. Results showed that ethanol treatment decreased viability by about 20% at concentrations of 0.1-0.5% ethanol and by 50% at 1.0% ethanol. Ethanol-related decreases in eye size were recorded at 6 days postfertilization (dpf) and were dose dependent. There were significant decreases in the volumes of the photoreceptor, inner nuclear, and ganglionic layers and in the lens of 9 dpf ethanol-exposed compared with control larvae. Ultrastructural examination showed signs of developmental lags in the ethanol-treated fish as well as abnormal retinal apoptosis in the 6 dpf ethanol-treated larvae compared with their controls. These results demonstrate that the developing zebrafish eye is sensitive to perturbation with ethanol and displays some of the eye deficits present in fetal alcohol syndrome.

Effects of ethanol on photoreceptors and visual function in developing zebrafish

PURPOSE

Children born to mothers who have consumed alcohol during pregnancy have an array of retinal abnormalities and visual dysfunctions. In the past, rodent systems have been used to study the teratogenic effects of ethanol on vertebrate embryonic development. The exact developmental windows in which ethanol causes specific developmental defects have been difficult to determine because rodents and other mammals develop in utero. In this study, we characterized how ethanol affects the function and development of the visual system in an ex utero embryonic system, the zebrafish.

METHODS

Zebrafish embryos were raised in fish water containing various concentrations of ethanol from 2 to 5 days after fertilization. The effects of ethanol on retinal morphology were assessed by histologic and immunohistochemical analyses and those on retinal function were analyzed by optokinetic response (OKR) and electroretinography (ERG).

RESULTS

Zebrafish embryos exposed to moderate and high levels of ethanol during early embryonic development had morphological abnormalities of the eye characterized by hypoplasia of the optic nerve and inhibition of photoreceptor outer segment growth. Ethanol treatment also caused an increased visual threshold as measured by the OKR. Analysis with the ERG indicated that there was a severe reduction of both the a- and b-waves, suggesting that ethanol affects the function of the photoreceptors. Indeed, low levels of ethanol that did not cause obvious morphologic changes in either the body or retina did affect both the OKR visual threshold and the a- and b-wave amplitudes.

CONCLUSIONS

Ethanol affects photoreceptor function at low concentrations that do not disturb retinal morphology. Higher levels of ethanol inhibit photoreceptor development and cause hypoplasia of the optic nerve.

Alterations in circadian rhythm phase shifting ability in rats following ethanol exposure during the third trimester brain growth spurt

BACKGROUND

Disruptions in sleep and feeding rhythms are among the consequences of prenatal alcohol exposure. Previously, we reported that ethanol exposure during the second trimester equivalent in rats produces long-lasting impairments in circadian system functioning. In the present study, we examined the effects of ethanol exposure during the third trimester equivalent brain growth spurt on the development of the circadian clock system.

METHODS

Sprague-Dawley male rat pups were exposed to 6.0 g/kg/d ethanol via an artificial rearing procedure on postnatal days (PD) 4 through 9 (EtOH). An artificially reared gastrostomized control group and a normally reared suckle control group were also included. At 10 to 12 weeks of age, wheel-running behavior was measured continuously under a 12-hour/12-hour light/dark (LD) cycle. Thereafter, subjects were exposed to a 6-hour phase delay of the LD cycle, and the ability to adjust to the new LD cycle was evaluated.

RESULTS

Before the phase delay, onset time of activity and acrophases of activity in all 3 groups were not significantly different from one another. After the 6-hour LD cycle delay, EtOH subjects were slower to adapt to the new cycle compared with both control groups, as measured by both activity onset and acrophase. Throughout the experiment, activity levels of EtOH subjects tended to be higher compared to both controls.

CONCLUSIONS

These data demonstrate that ethanol exposure during the third trimester disrupts the ability to synchronize circadian rhythm to light cues. Disruptions in circadian regulation may cause abnormal behavioral rhythmicity, such as disrupted sleep and feeding patterns, as seen in individuals prenatally exposed to ethanol.

The effect of in ovo ethanol exposure on retina and optic nerve in a chick embryo model system

Ocular anomalies seen in children with fetal alcohol syndrome (FAS) suggest that ocular structures are sensitive to alcohol exposure during their development. This study was designed to investigate the effect of in ovo ethanol (EtOH) exposure on retinal development and myelinization of optic nerve fibers at an ultra structural level in a chick embryo model system. Prior to incubation, fertilized chicken eggs were injected once with 100 microl of either 0.9% NaCl (vehicle control), or EtOH solutions at different doses (10, 30, or 50%, v:v in 0.9% NaCl) into their air sacs and incubated at 37.5 degrees C and saturation humidity. On day 20 embryos were analyzed in terms of their viability and growth and the optic cups including the optic nerves were dissected out. Specimens were processed for electron microscopy (EM). Results showed that, EtOH significantly decreased the viability of chick embryos (P < 0.045), and caused significant prenatal growth retardation (P < 0.004) in a dose-dependant manner. Light microscopy of semi thin sections revealed that prenatal exposure to EtOH resulted in both retinal degeneration and optic nerve hypoplasia (P < 0.001) in a dose-dependant manner. EM revealed that a dose-dependant decrease in the number of myelinated nerve fibers was profound in groups exposed to EtOH (P < 0.001). Furthermore, the myelin coats observed were thinner than those seen in control embryos. In groups exposed to EtOH myelin sheets were unorganized and contained vacuolar structures in between them. The tissue in between the cells and optic nerve fibers, on the other hand, lost its intact appearance with vacuolar and vesicular structures in between them. In addition, the optic nerve fibers contained granular accumulations in EtOH exposed groups. A dose dependent degeneration was also observed in retinas of EtOH exposed groups. The effect of EtOH was profound in pigment epithelium (PE), inner plexiform layer (IPL), and ganglion cell layer (GC). Mitochondrial deficiencies, and alterations in melanin granule number and distribution dominated the defects seen in PE. On the other hand, EM findings of all the affected layers were suggestive of induced cell death in EtOH exposed groups. Thus, this study suggests retinal development with the emphasis on melanin pigmentation in PE and optic nerve myelinization as potential targets of prenatal EtOH exposure and discusses potential mechanisms of EtOH action on these tissues.

Alcohol-Induced Lipid and Morphological Changes in Chick Retinal Development

BACKGROUND

Alcohol exposure causes alterations in the lipid content of different organs and a reduction of long-chain fatty acids. During embryo development, the central nervous system is extremely vulnerable to the teratogenic effects of alcohol, and the visual system is particularly sensitive.

METHODS

White Leghorn chick embryos were injected with 10- and 20-microl alcohol doses into the yolk sac at day 6 of incubation. The lipid composition of the retina was analyzed in embryos at day 7 of incubation (E7), E11, E15, and E18. The percentages of phospholipids, free cholesterol, esterified cholesterol, diacylglycerides, and free fatty acids were estimated by using an Iatroscan thin layer chromatography flame ionization detector. Gas chromatography and mass spectrometry were used to determine fatty acid composition. The morphological study was performed at E7, E11, and E19 by means of semithin and immunohistochemical techniques.

RESULTS

In the retina, alcohol causes the total lipid content to change, with a remarkable increase in free cholesterol and a dramatic decrease in esterified cholesterol. Diacylglycerides and free fatty acids tend to increase. Phosphatidylcholine and phosphatidylethanolamine decrease, whereas phosphatidylserine, sphingomyelin, and phosphatidylinositol increase. The main fatty acids of the retina also undergo changes. At E7, myriotic acid increases, and oleic acid and polyunsaturated fatty acids such as arachidonic acid and docosahexaenoic acid decrease. From E18 onward, there is some recovery, except for fatty acids, which recover earlier. From a morphological point of view, alcohol effects on retinal development are various: increase of intercellular spaces in all cell layers, pyknosis with loss of cellularity in the inner nuclear cell layer and ganglion cell layer, retarded or disorderly cell migration, early cell differentiation, and loss of immunoreactivity for myelin oligodendrocyte-specific protein.

CONCLUSIONS

Acute alcohol exposure during embryo development causes the lipid composition of the retina to change, with a trend to recovery in the last stages. These alterations are in line with the changes observed at a morphological level.

The protective role of squalene in alcohol damage in the chick embryo retina

The developing CNS, and in particular the visual system, is very sensitive to the effects of alcohol. Alcohol causes lipid peroxidation. Squalene, the major olive oil hydrocarbon, is a quencher of singlet oxygen and prevents the corresponding lipid peroxidation. We presumed that squalene can protect against the alcohol-induced damage already observed during the development of the chick retina. Alcohol+squalene was administered directly into the yolk sac of the egg of White Leghorn chicks at day 6 of incubation. The lipid composition of the retina was analyzed in embryos at E7, E11, E15 and E18. The proportions of phospholipids, free and esterified cholesterol, diacylglycerides and free fatty acids were estimated using the Iatroscan TLC/FID procedure. Gas chromatography and mass spectrometry were used to determine the fatty acid composition. The morphological study was carried out at E11 using semithin sections, and by means of immunohistochemical techniques at E19. Comparing the results obtained in control embryos, the administration of alcohol+squalene reduces the effects of alcohol on the total lipid composition of the retina during development. The effects were, in fact, of less magnitude than in embryos treated only with alcohol. The major phospholipid species of alcohol+squalene-treated embryos exhibited total recuperation at E15. As far as fatty acids are concerned, no significant changes were observed with regard to control embryos during development. From a morphological point of view, the retinas of alcohol+squalene-treated embryos show at E11 fewer cellular alterations than the retinas of alcohol-treated embryos. In this respect, the retinas of alcohol+squalene-treated embryos exhibited: a columnar cell arrangement similar to that observed in control retinas; few pycnotic cells and very few alterations in ganglion cell layers and in the optic nerve fibers layer. At E19 the recuperation of the expression of myelin oligodendrocyte specific protein (MOSP) in alcohol+squalene-treated embryos was recorded. Since squalene reduces the deleterious effects caused by alcohol on the lipid composition and the structure of the retina, squalene could act as a naturally occurring agent for the prevention of damage caused by abusive alcohol ingestion during pregnancy.

A critical role of Pax6 in alcohol-induced fetal microcephaly

Maternal alcohol abuse during pregnancy is one of the leading causes of birth defects in humans. Despite extensive studies, the molecular basis is still not clear. Here we transiently exposed Xenopus embryos to alcohol and showed that alcohol dose-dependently produced microcephaly and growth retardation. Moreover, it reduced the expression of several key neural genes (xPax6, xOtx2, xSox3, xSox2, and xNCAM), of which xPax6 was most vulnerable. An alcohol concentration as low as 0.3% could produce more than 90% reduction of xPax6 expression. Consistently, microinjection of xPax6 expression plasmid to Xenopus embryos dose-dependently rescued alcohol-induced microcephaly and restored the expression of xOtx2, xSox3, xSox2, and xNCAM. To test whether reactive oxygen species (ROS) is the upstream signal for alcohol-induced microcephaly and xPax6 suppression, we overexpressed catalase in Xenopus embryos and found that catalase not only decreased alcohol-induced H(2)O(2) formation, but also fully restored Pax6 expression and reversed microcephaly. In contrast, xPax6 and catalase could only provide partial protection against growth retardation. Results from this study illustrate for the first time the critical role of H(2)O(2)-mediated Pax6 suppression in alcohol-induced microcephaly and suggest the presence of additional mechanisms for alcohol-induced fetal growth retardation.

Effects of embryonic exposure to ethanol on zebrafish visual function

Across a variety of species, including humans, it has been shown that embryos exposed to ethanol display eye abnormalities as well as deficiencies in visual physiology and behavior. The purpose of this study was to examine the effects of embryonic exposure to ethanol on visual function in zebrafish. Visual function was assessed physiologically, via electroretinogram (ERG) recordings, and behaviorally, by measuring visual acuity with the optomotor response. Zebrafish larvae were exposed to 1.5% ethanol at various times during development, including the period of maximal eye development. The results show that ethanol effects on visual function were most pronounced when exposure occurred during eye development. ERG recordings from ethanol-exposed larvae differed from normal subjects both in shape of the response waveform and in visual thresholds under both light and dark adaptation; the differences were more pronounced under lower levels of adaptation. Also, ethanol-exposed larvae displayed lower visual acuity as determined from the optomotor response. These results indicate embryonic ethanol exposure affects visual function particularly when exposure occurs during eye development. In addition, these findings illustrate the usefulness of the zebrafish as a viable animal model for studying Fetal Alcohol Syndrome (FAS).

A selective loss of small-diameter myelinated optic nerve axons in rats prenatally exposed to ethanol

Pregnant rats were fed an ethanol-containing liquid diet between gestational days 10 and 21. The optic nerves of their litters at 49 days of age were examined using quantitative stereological procedures. Cross-sectional areas of the optic nerve in ethanol-exposed rats were significantly smaller than those in controls. This was reflected in the reduced number of myelinated fibers, but not of non-myelinated fibers. The size distribution histogram indicated a decreased number of small axonal-diameter myelinated fibers in ethanol-exposed rats. The results suggested optic nerve hypoplasia in ethanol-exposed rats characterized by a selective loss of small-diameter myelinated fibers.

[Fetal alcohol syndrome: nervous system damage and clinical phenotype]

Alcohol is much more slowly eliminated in the fetus than in the mother (< 50%). The ethanol and its derivative the acetaldehyde have a constant dose-effect on the development of the nervous system central. The individual susceptibility to alchol teratogenic effect in utero is responsible of variable clinical phenotype. This teratogenicity is constant during all the development of the central nervous system. The diagnosis of fetal alcohol syndrome (FAS) associates three criteria: delay of pre- and postnatal growth, abnormal development of the central nervous system, craniofacial abnormalities. Cerebral malformations are extremely variable, being to relate to the various stages of development of the nervous system central. Neurochimic abnormalities interest mainly the mono-aminergic system. The backwardness is the best known consequence of SAF (34 to 851%). It is not constant. Facial dysmorphic results of joint abnormalities whose none is pathognomonic but whose grouping is evocative. Psychomotor instability is the most frequent expression on the behavioral phenotype.