Selective fetal malnutrition: the fetal alcohol syndrome

Murine Models for the Study of Fetal Alcohol Spectrum Disorders: An Overview

Prenatal alcohol exposure is associated to different physical, behavioral, cognitive, and neurological impairments collectively known as fetal alcohol spectrum disorder. The underlying mechanisms of ethanol toxicity are not completely understood. Experimental studies during human pregnancy to identify new diagnostic biomarkers are difficult to carry out beyond genetic or epigenetic analyses in biological matrices. Therefore, animal models are a useful tool to study the teratogenic effects of alcohol on the central nervous system and analyze the benefits of promising therapies. Animal models of alcohol spectrum disorder allow the analysis of key variables such as amount, timing and frequency of ethanol consumption to describe the harmful effects of prenatal alcohol exposure. In this review, we aim to synthetize neurodevelopmental disabilities in rodent fetal alcohol spectrum disorder phenotypes, considering facial dysmorphology and fetal growth restriction. We examine the different neurodevelopmental stages based on the most consistently implicated epigenetic mechanisms, cell types and molecular pathways, and assess the advantages and disadvantages of murine models in the study of fetal alcohol spectrum disorder, the different routes of alcohol administration, and alcohol consumption patterns applied to rodents. Finally, we analyze a wide range of phenotypic features to identify fetal alcohol spectrum disorder phenotypes in murine models, exploring facial dysmorphology, neurodevelopmental deficits, and growth restriction, as well as the methodologies used to evaluate behavioral and anatomical alterations produced by prenatal alcohol exposure in rodents.

A comparison of the different animal models of fetal alcohol spectrum disorders and their use in studying complex behaviors

Prenatal ethanol exposure (PNEE) has been linked to widespread impairments in brain structure and function. There are a number of animal models that are used to study the structural and functional deficits caused by PNEE, including, but not limited to invertebrates, fish, rodents, and non-human primates. Animal models enable a researcher to control important variables such as the route of ethanol administration, as well as the timing, frequency and amount of ethanol exposure. Each animal model and system of exposure has its place, depending on the research question being undertaken. In this review, we will examine the different routes of ethanol administration and the various animal models of fetal alcohol spectrum disorders (FASD) that are commonly used in research, emphasizing their strengths and limitations. We will also present an up-to-date summary on the effects of prenatal/neonatal ethanol exposure on behavior across the lifespan, focusing on learning and memory, olfaction, social, executive, and motor functions. Special emphasis will be placed where the various animal models best represent deficits observed in the human condition and offer a viable test bed to examine potential therapeutics for human beings with FASD.

Prenatal substance abuse: short- and long-term effects on the exposed fetus

Prenatal substance abuse continues to be a significant problem in this country and poses important health risks for the developing fetus. The primary care pediatrician's role in addressing prenatal substance exposure includes prevention, identification of exposure, recognition of medical issues for the exposed newborn infant, protection of the infant, and follow-up of the exposed infant. This report will provide information for the most common drugs involved in prenatal exposure: nicotine, alcohol, marijuana, opiates, cocaine, and methamphetamine.

The impact of maternal age on the effects of prenatal alcohol exposure on attention

BACKGROUND

Prenatal exposure to alcohol has a variety of morphologic and neurobehavioral consequences, yet more than 10% of women continue to drink during pregnancy, placing their offspring at risk for fetal alcohol spectrum disorders (FASD). Identification of at-risk pregnancies has been difficult, in part, because the presence and severity of FASD are influenced by factors beyond the pattern of alcohol consumption. Establishing maternal characteristics, such as maternal age, that increase the risk of FASD is critical for targeted pregnancy intervention.

METHODS

We examined the moderating effect of maternal age on measures of attention in 462 children from a longitudinal cohort born to women with known alcohol consumption levels (absolute ounces of alcohol per day at conception) who were recruited during pregnancy. Analyses examined the impact of binge drinking, as average ounces of absolute alcohol per drinking day. Smoking and use of cocaine, marijuana, and opiates were also assessed. At 7 years of age, the children completed the Continuous Performance Test, and their teachers completed the Achenbach Teacher Report Form.

RESULTS

After controlling for covariates, stepwise multiple regression analyses revealed a negative relation between levels of prenatal binge drinking and several measures of attention. The interaction between alcohol consumption and maternal age was also significant, indicating that the impact of maternal binge drinking during pregnancy on attention was greater among children born to older drinking mothers.

CONCLUSION

These findings are consistent with previous findings that children born to older alcohol-using women have more deleterious effects of prenatal alcohol exposure on other neurobehavioral outcomes.

Hippocampal cell loss and neurogenesis after fetal alcohol exposure: insights from different rodent models

Prenatal ethanol exposure is invariably detrimental to the developing central nervous system and the hippocampus is particularly sensitive to the teratogenic effects of ethanol. Prenatal ethanol exposure has been shown to result in hippocampal cell loss, altered neuronal morphology and impaired performance on hippocampal-dependent learning and memory tasks in rodents. The dentate gyrus (DG) of the hippocampus is one of the few brain regions where neurogenesis continues into adulthood. This process appears to have functional significance and these newly generated neurons are believed to play important functions in learning and memory. Recently, several groups have shown that adult hippocampal neurogenesis is compromised in animal models of fetal alcohol spectrum disorders (FASD). The direction and magnitude of any changes in neurogenesis, however, appear to depend on a variety of factors that include: the rodent model used; the blood alcohol concentration achieved; the developmental time point when alcohol was administered; and the frequency of ethanol exposure. In this review we will provide an overview of the different rodent models of FASD that are commonly used in this research, emphasizing each of their strengths and limitations. We will also present an up-to-date summary on the effects of prenatal/neonatal ethanol exposure on adult hippocampal neurogenesis and cell loss, highlighting some of the possible molecular mechanisms that might be involved.

Ethanol and the placenta: A review

OBJECTIVE

In this paper we review published studies of alcohol exposure on placentation, placenta growth and function.

METHODS

We searched PubMed using the MeSH terms: placenta, ethanol, fetal alcohol syndrome and prenatal exposure with delayed effects. We searched the years 1996-2006 and used the references from other articles to expand our search. We limited the search to English only and human only. We excluded studies using choriocarcinoma and animal studies. We grouped the 66 papers into seven topic areas for ease of review.

RESULTS

Alcohol exposure is associated with placental dysfunction, decreased placental size, impaired blood flow and nutrient transport, endocrine changes, increased rates of stillbirth and abruption, umbilical cord vasoconstriction, and low birth weight.

CONCLUSIONS

Prenatal alcohol exposure has a broad range of adverse effects on placental development and function. Additional research on placental development from populations with heavy alcohol exposure should be encouraged. A tissue bank of placentas with detailed assessment of exposure to alcohol, smoking and other relevant data should be considered as a repository to support additional research.

The effect of acute, chronic, and prenatal ethanol exposure on insulin sensitivity

Ethanol has been considered as a lifestyle factor that may influence the risk of type 2 diabetes mellitus. In healthy adults, acute ethanol consumption results in insulin resistance. Acute ethanol consumption causes insulin resistance selectively in skeletal muscle by an indirect mechanism. Possible mediators include triglycerides (TGs), catecholamines, acetaldehyde, alterations in insulin binding, and hepatic insulin sensitizing substance (HISS). Recent studies in rats showed that acute administration of ethanol causes insulin resistance in a dose-dependent manner that is secondary to the blockade of insulin-induced HISS release. Chronic ethanol consumption may improve insulin sensitivity, but the results from the randomized controlled trials are mixed. Differences in ethanol dose, consumption period, and abstention period may account for the discrepant results. Epidemiological studies have suggested that the relationship between ethanol and insulin sensitivity is either an inverted U-shape or a positive linear relationship. Future randomized controlled trials should consider the dose of ethanol and the duration of ethanol consumption and abstention in the experimental design. Chronic prenatal and postnatal (nursing) ethanol exposure results in insulin resistance that is secondary to the absence of HISS release/action with the HISS-independent insulin action and insulin-like growth factor-1 (IGF-1)-mediated glucose disposal action remaining unimpaired. The impaired HISS release may be related to a reduction in hepatic glutathione (GSH) levels. The effect of chronic ethanol consumption on HISS has not been evaluated.

Increased incidence of hepatic insulin-sensitizing substance (HISS)-dependent insulin resistance in female rats prenatally exposed to ethanol

Insulin causes the release of the hepatic insulin-sensitizing substance (HISS) from the liver. Hepatic parasympathetic nerves play a permissive role in the release of HISS. HISS-dependent insulin resistance (HDIR) occurs in the absence of HISS. Fetal ethanol exposure has been shown to cause dose-dependent HDIR in adult male rat offspring. Since female offspring are more severely affected by in utero ethanol toxicity, we hypothesized that fetal alcohol exposure causes higher incidence and more severe HDIR in adult female offspring. Adult female rat offspring prenatally exposed to different concentrations of ethanol (0%, 15%, and 20%) were tested for insulin sensitivity using the rapid insulin sensitivity test (RIST). The RIST index was significantly reduced in the 15% (134.1 ± 16.1 mg/kg) and the 20% (98.7 ± 9.7 mg/kg) group compared with the 0% (220.9 ± 27.6 mg/kg) group. Administration of atropine produced significant additional HDIR in the 15% group (82.9 ± 14.5 mg/kg) but not the 20% group (83.8 ± 20.5 mg/kg) indicating complete HDIR had been produced in this group, contrary to the adult male offspring in a previous study. The results are consistent with the hypothesis that adult-female offspring are more severely affected by in utero ethanol exposure compared with adult-male offspring.Key words: fetal, alcohol, insulin resistance, gender, HISS, teratology, diabetes.

Maternal Age, Alcohol Abuse History, and Quality of Parenting as Moderators of the Effects of Prenatal Alcohol Exposure on 7.5-Year Intellectual Function

BACKGROUND

In contrast to the extensive literature documenting IQ deficits in patients with fetal alcohol syndrome, effects on IQ have not generally been reported for children with alcohol-related neurodevelopmental disorder (ARND). This study examined the role of maternal age, MAST, and quality of parenting in moderating the effects of prenatal alcohol exposure on the WISC-III IQ test in moderate-to-heavily exposed children.

METHODS

A total of 337 inner-city African American children whose mothers were recruited prenatally were administered the WISC-III at 7.5 years. Alcohol exposure was assesed with a timeline follow-back interview administered at every prenatal clinic visit. Moderating effects of the three risk factors were examined by adding interaction terms to regression analyses and dichotomizing the moderators and performing separate regressions on the two groups.

RESULTS

Prenatal alcohol exposure was related to WISC-III Freedom from Distractibility but not to Full Scale IQ for the sample as a whole. However, among children born to older mothers, an alcohol effect emerged on Full Scale IQ and five of seven composite IQ scores. Similarly, adverse effects were seen among children of MAST-positive mothers and children whose parents provided less optimal cognitive stimulation. Each additional ounce of absolute alcohol consumed per day during pregnancy was associated with a 2.9-point decrease in Full Scale IQ and a 5.6-point decrement on Freedom from Distractibility.

CONCLUSIONS

This study is the first to demonstrate IQ effects among children with ARND born to older and MAST-positive mothers, particularly in relation to first-trimester drinking. These findings suggest that there are subgroups of more vulnerable and severely affected children whose intellectual performance is compromised. A moderate- to heavy-drinking mother who has given birth to an unaffected child when she was younger needs to be warned that her risk of having an adversely affected child increases as she grows older.

Comparative effects of developmental thiamine deficiencies and ethanol exposure on the morphometry of the CA3 pyramidal cells

Maternal alcoholism and thiamine deficiency are frequently considered to be the causal agents of the central nervous system (CNS) damage associated with mental retardation in the offspring. For further understanding of pathological mechanisms underlying CNS damage in both disorders, histological studies were undertaken in developing rats to compare the hippocampus CA3 pyramidal cells measurements and density between three patterns of thiamine deficiency and chronic alcohol exposure. Female rats were given thiamine-deficient diet during different periods of gestation and lactation to obtain pre-, peri-, and postnatal thiamine-deficient pups. Twelve percent ethanol/water drinking fluid was given to mothers throughout gestation and lactation to obtain ethanol-exposed pups. Thiamine was administered during developmental ethanol exposure to assess the extent of interference between ethanol and thiamine metabolism. Nondrug-treated dams were allowed ad lib access to food and water during gestation and lactation to yield control pups. Hippocampus histology was performed in 45-day-old rats, and the CA3 pyramidal cells measurements and density assessed and compared between all treatment groups. It appears that the mean nuclear size of pyramidal cells in the field CA3 was significantly reduced in all the treatments compared to the control. While the mean nuclear size decreased more severely in development ethanol exposure than in the three patterns of thiamine deficiency, no significant difference was noted when pre-, peri-, and postnatal thiamine-deficient rats were compared. However, thiamine administration during developmental ethanol exposure partially restored the mean nuclear size. In contrast, comparisons between ethanol-exposed pups and the three patterns of thiamine-deficient pups, exhibited similar intensity in the deficit of CA3 pyramidal cells. Cell loss generated by ethanol treatment was not suppressed by thiamine administration. Common and separate mechanisms underlying the effects of alcohol intoxication and thiamine deficiency on cell death and cell atrophy were suggested.

Sex differences in the human corpus callosum: myth or reality?

It has been claimed that the human corpus callosum shows sex differences, and in particular that the splenium (the posterior portion) is larger in women than in men. Data collected before 1910 from cadavers indicate that, on average, males have larger brains than females and that the average size of their corpus callosum is larger. A meta-analysis of 49 studies published since 1980 reveals no significant sex difference in the size or shape of the splenium of the corpus callosum, whether or not an appropriate adjustment is made for brain size using analysis of covariance or linear regression. It is argued that a simple ratio of corpus callosum size to whole brain size is not an appropriate way to analyse the data and can create a false impression of a sex difference in the corpus callosum. The recent studies, most of which used magnetic resonance imaging (MRI), confirm the earlier findings of larger average brain size and overall corpus callosum size for males. The widespread belief that women have a larger splenium than men and consequently think differently is untenable. Causes of and means to avoid such a false impression in future research are discussed.

What research with animals is telling us about alcohol-related neurodevelopmental disorder

The substantial advances in understanding fetal alcohol syndrome over the past 20 years were made in large part because of research with animals. This review illustrates recent progress in animal research by focusing primarily on the central nervous system effects of prenatal alcohol exposure. Current findings suggest further progress in understanding consequences, risk factors, mechanisms, prevention and treatment will depend on continued research with animals.

Increased vulnerability to alcohol-related birth defects in the offspring of mothers over 30

The risk of fetal alcohol syndrome (FAS) is known to increase with increased maternal age and parity. This study investigated the hypothesis that the deficits in growth and intellectual function seen in non-FAS infants exposed to alcohol at moderate-to-heavy levels are also found disproportionately in the offspring of older mothers. Mothers of 480 African-American, inner-city infants were interviewed at each prenatal clinic visit regarding their use of alcohol during pregnancy. Infants were assessed for physical growth and cognitive development repeatedly through age 13 months. In analyses run separately for the infants of younger and older mothers, alcohol-related deficits were seen most strongly in the offspring of women over 30 years of age. This pattern was not caused by lower levels of drinking by the younger mothers. Age-related increases in maternal body fat-to-water ratio and a faster rate of alcohol metabolism in chronic drinking women may account for the greater vulnerability of the offspring of the older mothers. These data suggest that physiological changes associated with aging and/or chronic drinking may play an important role in the alcohol-related birth defects seen in infants exposed at moderate-to-heavy levels.

Maternal risk factors in fetal alcohol syndrome: provocative and permissive influences

We present an hypothesis integrating epidemiological, clinical case, and basic biomedical research to explain why only relatively few women who drink alcohol during pregnancy give birth to children with alcohol-related birth defects (ARBDs), in particular, Fetal Alcohol Syndrome (FAS). We argue that specific sociobehavioral risk factors, e.g., low socioeconomic status, are permissive for FAS in that they provide the context for increased vulnerability. We illustrate how these permissive factors are related to biological factors, e.g., decreased antioxidant status, which in conjunction with alcohol, provoke FAS/ARBDs in vulnerable fetuses. We propose an integrative heuristic model hypothesizing that these permissive and provocative factors increase the likelihood of FAS/ARBDs because they potentiate two related mechanisms of alcohol-induced teratogenesis, specifically, maternal/fetal hypoxia and free radical formation.

The consequences of prenatal substance use for the developing fetus, newborn, and young child

Although substance use has been a worldwide problem at all levels of society since ancient times, recent attention has been focused on the use of legal and illegal substances by the pregnant woman. Almost all drugs taken by the pregnant woman are known to cross the placenta and have some effect on the fetus. This article reviews the effects of the drugs most frequently used by pregnant women in the United States--nicotine, alcohol, marijuana, opiates, and cocaine--on the fetus and neonate; when possible, information regarding long-term medical problems is included.

Prenatal malnutrition and development of the brain

In this review, we have summarized various aspects as to how prenatal protein malnutrition affects development of the brain and have attempted to integrate several broad principles, concepts, and trends in this field in relation to our findings and other studies of malnutrition insults. Nutrition is probably the single greatest environmental influence both on the fetus and neonate, and plays a necessary role in the maturation and functional development of the central nervous system. Prenatal protein malnutrition adversely affects the developing brain in numerous ways, depending largely on its timing in relation to various developmental events in the brain and, to a lesser extent, on the type and severity of the deprivation. Many of the effects of prenatal malnutrition are permanent, though some degree of amelioration may be produced by exposure to stimulating and enriched environments. Malnutrition exerts its effects during development, not only during the so-called brain growth spurt period, but also during early organizational processes such as neurogenesis, cell migration, and differentiation. Malnutrition results in a variety of minimal brain dysfunction-type syndromes and ultimately affects attentional processes and interactions of the organism with the environment, in particular producing functional isolation from the environment, often leading to various types of learning disabilities. In malnutrition insult, we are dealing with a distributed, not focal, brain pathology and various developmental failures. Quantitative assessments show distorted relations between neurons and glia, poor formation of neuronal circuits and alterations of normal regressive events, including cell death and axonal and dendritic pruning, resulting in modified patterns of brain organization. Malnutrition insult results in deviations in normal age-related sequences of brain maturation, particularly affecting coordinated development of various cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter systems. It is obvious that such diffuse type "lesions" can be adequately assessed only by interdisciplinary studies across a broad range of approaches, including morphological, biochemical, neurophysiological, and behavioral analyses.

Effect of dietary calcium on the colonic luminal environment

Dietary supplementation with calcium may prevent the development of colorectal cancer. This mechanism may be related to fatty acid and bile salt chelation in the small bowel forming non-toxic calcium-soap compounds. Calcium may also act locally or systemically on the colonic mucosa. Faecal concentrations of free fatty acids and free bile acids were measured in 17 Sprague-Dawley rats (weighing 472 (39 g)) whose daily calcium intake had been trebled by enriching the chow and adding calcium lactate (24 g/l) to the drinking water. Mean (SEM) faecal concentrations of free bile acids were 33% less than in 19 controls (1.23 (0.15) v 1.82 (0.20) mg/g; p less than 0.001), whereas free fatty acid concentrations were 117% higher (14.68 (3.59) v 6.76 (2.41) mg/g; p less than 0.02). The 'direct' effect of calcium was assessed by organ culture of rat colonic explants in three different concentrations of calcium. Crypt cell production rate (measured by a stathmokinetic technique), which was (mean (SEM)) 4.80 (0.23) cells/crypt/h in control medium (Ca2+ = 2.14 mmol/l), fell by 43% when calcium concentration was doubled (p less than 0.05) and by a further 43% when the concentration was trebled (p less than 0.02). Calcium binds free fatty acids but not free bile acids intraluminally. Calcium has a direct antitropic action on colonic crypts.

The consequences of maternal substance abuse for the child exposed in utero

The marked increase in substance abuse in the United States represents a significant risk to the development of children exposed in utero to tobacco, alcohol, and illicit drugs. This paper reviews the current literature exploring the effects of the major substances of abuse on in utero and childhood development.

Gestational alcoholism and fetal zinc accretion in Long-Evans rats

An animal study was conducted to examine the effects of alcohol consumption on placental transfer of zinc during late gestation. Throughout pregnancy, rat dams were fed a nutritionally adequate diet with 30% of total kcal as alcohol. On days 18 and 21 of pregnancy, zinc-65 was injected subcutaneously into the dams and the dams were killed 24 hours later; tissues were removed for analyses. Maternal serum, liver, kidney, and heart zinc decreased with gestational age while total fetal zinc increased. Neither the decrease in maternal organ zinc nor fetal accretion were affected by alcohol consumption. Placental zinc concentration also declined with developmental age and was not influenced by alcohol consumption. The decrease in placental zinc was accompanied by a decrease in zinc associated with 4-10-kD proteins of placental cytosol. Our results suggest that zinc flux during late rat gestation is a well-regulated process that is not influenced by alcohol consumption. Coordination of the transfer apparently is influenced by maternal blood concentration of zinc, placental zinc-binding proteins, and fetal demand for zinc.