Effects of the maternal consumption of alcohol on alcohol selection in rats

Prenatal Alcohol Exposure as a Case of Involuntary Early Onset of Alcohol Use: Consequences and Proposed Mechanisms From Animal Studies

Prenatal alcohol exposure has been found to be an important factor determining later consumption of this drug. In humans, despite the considerable diversity of variables that might influence alcohol consumption, longitudinal studies show that maternal alcohol intake during gestation is one of the best predictors of later alcohol use from adolescence to young adulthood. Experimental studies with animals also provide abundant evidence of the effects of prenatal alcohol exposure on later alcohol intake. In addition to increased consumption, other effects include enhanced palatability and attractiveness of alcohol flavor as well as sensitization to its sensory and reinforcing effects. Most of these outcomes have been obtained after exposing rats to binge-like administrations of moderate alcohol doses during the last gestational period when the fetus is already capable of detecting flavors in the amniotic fluid and learning associations with aversive or appetitive consequences. On this basis, it has been proposed that one of the mechanisms underlying the increased acceptance of alcohol after its prenatal exposure is the acquisition (by the fetus) of appetitive learning via an association between the sensory properties of alcohol and its reinforcing pharmacological effects. It also appears that this prenatal appetitive learning is mediated by the activation of the opioid system, with fetal brain acetaldehyde playing an important role, possibly as the main chemical responsible for its activation. Here, we review and analyze together the results of all animal studies testing these hypotheses through experimental manipulation of the behavioral and neurochemical elements of the assumed prenatal association. Understanding the mechanisms by which prenatal alcohol exposure favors the early initiation of alcohol consumption, along with its role in the causal pathway to alcohol disorders, may allow us to find strategies to mitigate the behavioral effects of this early experience with the drug. We propose that prenatal alcohol exposure is regarded as a case of involuntary early onset of alcohol use when designing prevention policies. This is particularly important, given the notion that the sooner alcohol intake begins, the greater the possibility of a continued history of alcohol consumption that may lead to the development of alcohol use disorders.

Prenatal exposure to ethanol stimulates hypothalamic CCR2 chemokine receptor system: Possible relation to increased density of orexigenic peptide neurons and ethanol drinking in adolescent offspring

Clinical and animal studies indicate that maternal consumption of ethanol during pregnancy increases alcohol drinking in the offspring. Possible underlying mechanisms may involve orexigenic peptides, which are stimulated by prenatal ethanol exposure and themselves promote drinking. Building on evidence that ethanol stimulates neuroimmune factors such as the chemokine CCL2 that in adult rats is shown to colocalize with the orexigenic peptide, melanin-concentrating hormone (MCH) in the lateral hypothalamus (LH), the present study sought to investigate the possibility that CCL2 or its receptor CCR2 in LH is stimulated by prenatal ethanol exposure, perhaps specifically within MCH neurons. Our paradigm of intraoral administration of ethanol to pregnant rats, at low-to-moderate doses (1 or 3g/kg/day) during peak hypothalamic neurogenesis, caused in adolescent male offspring twofold increase in drinking of and preference for ethanol and reinstatement of ethanol drinking in a two-bottle choice paradigm under an intermittent access schedule. This effect of prenatal ethanol exposure was associated with an increased expression of MCH and density of MCH(+) neurons in LH of preadolescent offspring. Whereas CCL2(+) cells at this age were low in density and unaffected by ethanol, CCR2(+) cells were dense in LH and increased by prenatal ethanol, with a large percentage (83-87%) identified as neurons and found to colocalize MCH. Prenatal ethanol also stimulated the genesis of CCR2(+) and MCH(+) neurons in the embryo, which co-labeled the proliferation marker, BrdU. Ethanol also increased the genesis and density of neurons that co-expressed CCR2 and MCH in LH, with triple-labeled CCR2(+)/MCH(+)/BrdU(+) neurons that were absent in control rats accounting for 35% of newly generated neurons in ethanol-exposed rats. With both the chemokine and MCH systems believed to promote ethanol consumption, this greater density of CCR2(+)/MCH(+) neurons in the LH of preadolescent rats suggests that these systems function together in promoting alcohol drinking during adolescence.

Pharmacological ceramide reduction alleviates alcohol-induced steatosis and hepatomegaly in adiponectin knockout mice

Hepatosteatosis, the ectopic accumulation of lipid in the liver, is one of the earliest clinical signs of alcoholic liver disease (ALD). Alcohol-dependent deregulation of liver ceramide levels as well as inhibition of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPAR-α) activity are thought to contribute to hepatosteatosis development. Adiponectin can regulate lipid handling in the liver and has been shown to reduce ceramide levels and activate AMPK and PPAR-α. However, the mechanisms by which adiponectin prevents alcoholic hepatosteatosis remain incompletely characterized. To address this question, we assessed ALD progression in wild-type (WT) and adiponectin knockout (KO) mice fed an ethanol-containing liquid diet or isocaloric control diet. Adiponectin KO mice relative to WT had increased alcohol-induced hepatosteatosis and hepatomegaly, similar modest increases in serum alanine aminotransferase, and reduced liver TNF. Restoring circulating adiponectin levels using recombinant adiponectin ameliorated alcohol-induced hepatosteatosis and hepatomegaly in adiponectin KO mice. Alcohol-fed WT and adiponectin KO animals had equivalent reductions in AMPK protein and PPAR-α DNA binding activity compared with control-fed animals. No difference in P-AMPK/AMPK ratio was detected, suggesting that alcohol-dependent deregulation of AMPK and PPAR-α in the absence of adiponectin are not primary causes of the observed increase in hepatosteatosis in these animals. By contrast, alcohol treatment increased liver ceramide levels in adiponectin KO but not WT mice. Importantly, pharmacological inhibition of de novo ceramide synthesis in adiponectin KO mice abrogated alcohol-mediated increases in liver ceramides, steatosis, and hepatomegaly. These data suggest that adiponectin reduces alcohol-induced steatosis and hepatomegaly through regulation of liver ceramides, but its absence does not exacerbate alcohol-induced liver damage.

Prenatal ethanol exposure increases ethanol intake and reduces c-Fos expression in infralimbic cortex of adolescent rats

Prenatal ethanol exposure significantly increases later predisposition for alcohol intake, but the mechanisms associated with this phenomenon remain hypothetical. This study analyzed (Experiment 1) ethanol intake in adolescent inbred WKAH/Hok Wistar rats prenatally exposed to ethanol (2.0g/kg) or vehicle, on gestational days 17-20. Subsequent Experiments (2, 3 and 4) tested several variables likely to underlie the effect of gestational ethanol on adolescent ethanol preference, including ethanol-induced locomotor activation (LMA), ethanol-induced emission of ultrasonic vocalizations (USVs) after exposure to a rough exteroceptive stimulus, and induction of the immediate early gene C-fos in brain areas associated with processing of reward stimuli and with the retrieval and extinction of associative learning. Prenatal ethanol induced a two-fold increase in ethanol intake. Adolescents exhibited significant ethanol-induced LMA, emitted more aversive than appetitive USVs, and postnatal ethanol administration significantly exacerbated the emission of USVs. These effects, however, were not affected by prenatal ethanol. Adolescents prenatally exposed to ethanol as fetuses exhibited reduced neural activity in infralimbic cortex (but not in prelimbic cortex or nucleus accumbens core or shell), an area that has been implicated in the extinction of drug-mediated associative memories. Ethanol metabolism was not affected by prenatal ethanol. Late gestational exposure to ethanol significantly heightened drinking in the adolescent offspring of an inbred rat strain. Ethanol-induced LMA and USVs were not associated with differential ethanol intake due to prenatal ethanol exposure. Prenatal ethanol, however, altered basal neural activity in the infralimbic prefrontal cortex. Future studies should analyze the functionality of medial prefrontal cortex after prenatal ethanol and its potential association with predisposition for heightened ethanol intake.

The effect of gestational ethanol exposure on voluntary ethanol intake in early postnatal and adult rats

Clinical and epidemiological studies provide strong data for a relationship between prenatal ethanol exposure and the risk for abuse in adolescent and young adult humans. However, drug-acceptance results in response to fetal exposure have differed by study, age at evaluation, and experimental animal. In the present study, the authors tested whether voluntary ethanol intake was enhanced in both the infantile and adult rat (15 and 90 days of age, respectively), as a consequence of chronic fetal drug experience. Experimental rats were exposed in utero by administering ethanol to a pregnant dam in a liquid diet during gestational Days 6-20. Compared with those for isocaloric pair-fed and ad lib chow control animals, the results for experimental animals demonstrated that fetal exposure significantly increased infantile affinity for ethanol ingestion without affecting intake patterns of an alternative fluid (water). Heightened affinity for ethanol was absent in adulthood. Moreover, the results argue against malnutrition as a principal factor underlying the infantile phenomenon. These data add to a growing literature indicative of heightened early postnatal acceptance patterns resulting from maternal use or abuse of ethanol during pregnancy.

Experience-induced fetal plasticity: the effect of gestational ethanol exposure on the behavioral and neurophysiologic olfactory response to ethanol odor in early postnatal and adult rats

Human fetal ethanol exposure is strongly associated with ethanol avidity during adolescence. Evidence that intrauterine olfactory experience influences chemosensory-guided postnatal behaviors suggests that an altered response to ethanol odor resulting from fetal exposure may contribute to later abuse risk. Using behavioral and neurophysiological methods, the authors tested whether ethanol exposure via the dam's diet resulted in an altered responsiveness to ethanol odor in infant and adult rats. Compared with controls, (a) fetal exposure tuned the neurophysiologic response of the olfactory epithelium to ethanol odor at some expense to its responsiveness to other odorants in infantile rats--this effect was absent in adults; (b) the neural effect in infantile rats was paralleled by an altered behavioral response to ethanol odor that was specific to this odorant--this effect was also absent in adults; and (c) a significant component of the infantile behavioral effect was attributable to ethanol's effect on the olfactory neural modality. These data provide evidence for an important relationship between prenatal ethanol experience and postnatal behavioral responsiveness to the drug that is modulated or determined by olfactory function.

Increased ethanol intake after prenatal ethanol exposure: studies with animals

This review analyses the most relevant studies in which ethanol intake was measured after prenatal exposure to the drug. Despite the variety in methodology, in most such studies this prenatal experience induced a higher consumption of ethanol. Several variables that may affect the expression of this phenomenon are discussed, such as gender, age at testing, period of ethanol exposure, ethanol dose and conditions during the test. The mechanisms proposed in all these studies to explain the increased ethanol intake effect are also discussed. Some of these mechanisms are related to the teratological effects of the drug on the neurochemical systems involved in the reinforcing effects of abuse drugs, as well as on the regulatory systems of stress response. Another explanation of this phenomenon is also proposed in terms of associative learning. Specifically, the increased ethanol intake effect may be the result of a conditioned preference for ethanol acquired by the fetus when exposed to the drug during the last days of gestation.

Fetal or Infantile Exposure to Ethanol Promotes Ethanol Ingestion in Adolescence and Adulthood: A Theoretical Review

BACKGROUND

Despite good evidence that ethanol abuse in adulthood is more likely the earlier human adolescents begin drinking, it is unclear why the early onset of drinking occurs in the first place. A review of experimental studies with animals complemented by clinical, epidemiologic and experimental studies with humans supports the idea that precipitating conditions for ethanol abuse occur well before adolescence, in terms of very early exposure to ethanol as a fetus or infant. Experimental studies with animals indicate, accordingly, that ethanol intake during adolescence or adulthood is potentiated by much earlier exposure to ethanol as a fetus or infant.

METHODS

Two broad theoretical frameworks are suggested to explain the increase in affinity for ethanol that follows very early exposure to ethanol, one based on effects of mere exposure and the other on associative conditioning. Studied for 50 years or more in several areas of psychology, "effects of mere exposure" refers to enhanced preference expressed for flavors, or just about any stimuli, that are relatively familiar. An alternative framework, in terms of associative conditioning, is guided by this working hypothesis: During ethanol exposure the fetus or infant acquires an association between ethanol's orosensory (odor/taste) and pharmacological consequences, causing the animal subsequently to seek out ethanol's odor and taste.

RESULTS AND CONCLUSIONS

The implication that ethanol has rewarding consequences for the fetus or young infant is supported by recent evidence with perinatal rats. Paradoxically, several studies have shown that such early exposure to ethanol may in some circumstances make the infant treat ethanol-related events as aversive, and yet enhanced intake of ethanol in adolescence is nevertheless a consequence. Alternative interpretations of this paradox are considered among the varied circumstances of early ethanol exposure that lead subsequently to increased affinity for ethanol.

Long lasting effects of rearing by an ethanol-consuming dam on voluntary ethanol consumption by rats

For exposure to alcohol early in life to potentiate alcohol abuse in adolescence or adulthood, consequences of early exposure to alcohol must be of considerable duration. In two experiments using Norway rats as subjects, we examined effects of exposure during weaning to a dam consuming ethanol on adolescents' later affinity for ethanol. In a preliminary experiment, we offered rat pups a choice between 8% ethanol and water for 7 days immediately after they were weaned at 26 days of age. Pups whose dam had ingested 8% ethanol for 6 days either immediately or 1 week before we weaned them drank more ethanol than pups whose dam drank only water during the same period. Independent groups of rats reared by a dam consuming 8% ethanol from postnatal days 18 to 26 and tested 1, 2, 4 or 6 weeks later all drank significantly more 8% ethanol at testing than did pups whose dam drank only water. Our data also provided confirmation of previous reports of an experience-independent greater affinity for ethanol in younger rats.

Prenatal ethanol exposure has differential effects on fetal growth and skeletal ossification

There is increasing evidence suggesting that the intrauterine environment may influence long-term bone health and the risk of developing osteoporosis in later life. Alcohol (ethanol) is one factor whose presence in the prenatal environment has long-term consequences for the offspring, including permanent growth retardation. Moreover, prenatal ethanol exposure retards both fetal and postnatal bone development. It is unknown if ethanol's effects on skeletal development result from generalized growth retardation or effects specific to skeletal development. Furthermore, the level of ethanol exposure required to produce skeletal effects is unknown. The objectives of this study were to determine (1) if ethanol exerts specific effects on fetal skeletal development that are independent from its effects on general growth, and (2) the level of prenatal ethanol exposure required to affect fetal growth and skeletal ossification. Rats were fed isocaloric diets with ethanol (15%, 25%, or 36% ethanol-derived calories (EDC), approximating low, moderate, and high exposure levels), or without ethanol (pair-fed, PF, or control, C groups), prior to and throughout 21 days of gestation. The degree of E-induced delay in development was determined by comparison of E fetuses on d21 gestation to C fetuses on d17-d21 gestation. Prenatal ethanol exposure at 36% EDC decreased fetal body weight, length, and skeletal ossification compared with PF and C fetuses on d21 gestation. Importantly, effects on ossification, but not body weight or length, were also seen at the more moderate dose of 25% EDC, and the number of bones affected and the severity of effects on ossification tended to increase with dose of ethanol. Comparison of E fetuses on d21 gestation with C fetuses from d17 to 21 gestation indicated that the ethanol-induced delay in development differed for weight and skeletal ossification, and was not uniform among skeletal sites. Taken together, these data suggest that prenatal ethanol exposure has effects on fetal skeletal development that are independent of those on overall fetal growth, and that these effects occur even at moderate levels of maternal drinking. Effects of prenatal ethanol exposure on fetal skeletal development could potentially increase the offspring's risk of osteoporosis later in life.

Ethanol consumption by rat dams during gestation, lactation and weaning increases ethanol consumption by their adolescent young

In two experiments, we examined effects of ethanol consumption in rat dams during gestation, lactation, and weaning on voluntary ethanol consumption by their adolescent young. We found that exposure to an ethanol-ingesting dam throughout gestation, lactation, and weaning enhanced voluntary ethanol consumption by 26- to 33-day-old adolescents. We systematically examined effects on adolescent ethanol intake or requiring dams to drink ethanol during various periods in their pups' development. We found that exposure to an ethanol-consuming dam during weaning enhanced adolescent ethanol consumption and exposure to a dam drinking ethanol during either gestation or while nursing enhanced adolescents' ethanol consumption only if pups also had access to ethanol during the weaning period.

Effects of in utero administration of alcohol on glutathione levels in brain and liver

Previous studies in our laboratory have shown that the ontogenic development of gamma-glutamyltranspeptidase (gamma-GTP) activity is delayed by the in utero administration of alcohol. gamma-GTP is responsible for the degradation and recycling of glutathione (GSH) via the gamma-glutamyl cycle. In this study, we examined the effects of the in utero administration of alcohol on GSH levels in gestational age 21-day-old (g21) rats. Pregnant rats were placed on a liquid diet containing either 35% ethanol-derived calories (35% EDC) or a pair-fed (PF) diet or a lab chow (LC) diet starting on day 1 of gestation and maintained on their respective diets until gestational day 21. On gestational day 21, the pups were delivered by Cesarean section and brains and livers removed and prepared for analysis of GSH, gamma-GTP, or gamma-glutamyl-cysteine synthetase (gamma-GCSyn). GSH levels in brain and liver were found to be significantly lower in the offspring of the 35% EDC-treated mothers than from the PF and LC controls. gamma-GTP activity was higher in brain and liver of the 35% EDC group than the PF group. gamma-GCSyn, the enzyme involved in the rate-limiting step of GSH synthesis, was not affected in liver, but was found to be decreased in brain of the 35% EDC and PF groups when compared with the LC group. GSH is involved in many cellular reactions that appear to protect the cell from damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of in utero administration of alcohol on alcohol sensitivity in adult rats

In utero exposure to alcohol has been associated with many physical deficits and behavioral abnormalities. The purpose of these studies was to determine the effects of in utero administration of alcohol on behaviors related to tolerance and sensitivity to alcohol in adult rats. Pregnant rats were maintained on a liquid diet containing alcohol [35% ethanol-derived calories (EDC)] throughout pregnancy. Offspring manifested physical characteristics of Fetal Alcohol Syndrome. The 35% EDC group was able to stay on a wooden dowel longer and at higher blood alcohol concentrations than were pair-fed controls. Following a hypnotic dose of alcohol, rats in the 35% EDC group slept longer than pair-fed controls. A greater alcohol-induced hypothermic effect was seen in females in the 35% EDC group than in controls. Treatment did not affect rate of metabolism of alcohol. These studies suggest that in utero administration of alcohol may be a factor in determining an individual's sensitivity and tolerance to alcohol and possibly their preference for alcohol.

The effects of prenatal alcohol exposure on radial arm maze performance in adult rats

The hippocampal formation is sensitive to the in utero exposure to ethanol. It is one brain area thought to play an important role in spatial memory. We examined radial arm maze performance in rats exposed to ethanol prenatally. Pregnant rats were placed into the following treatment groups: LC, 17% EDC (ethanol-derived calories), 35% EDC, PF 35% or PF 17%. The LC group was fed lab chow and water ad lib, the 17% EDC and 35% EDC groups were fed a liquid diet containing either 3.3% or 6.7% v/v ethanol, respectively. Pair-fed controls were fed the same volume of an isocaloric diet as was consumed by their respective ethanol-treated groups. At birth, litters were culled to six and cross fostered to untreated surrogate mothers. Testing was initiated at 60 days of age and continued until the test criterion was satisfied. One-half of the rats in the 35% EDC group did not reach criterion. The remainder of the 35% EDC group and the 17% EDC rats attained criterion but required twice as many trials as their respective pair-fed controls. These results suggest that in utero administration of ethanol affects spatial memory capacity in rat, an observation consistent with other deficits seen in hippocampus of rats prenatally exposed to ethanol.

Effects of prenatal alcohol on gamma-glutamyl transpeptidase in various brain regions

Prenatal exposure of rats to alcohol produces morphological, biochemical, behavioral and physiological abnormalities. The enzyme gamma-glutamyl transpeptidase activity is increased when an animal is exposed to alcohol chronically. We examined the effect of the in utero exposure to alcohol on the regional brain distribution of gamma-GTP. Pregnant rats were placed into the following treatment groups: LC (ad lib lab chow and water), PF (pair-fed), 10% EDC (ethanol derived calories), 20% EDC and 35% EDC. The LC group was fed lab chow and water ad lib, the PF, 10% EDC, 20% EDC and 35% EDC groups were fed a liquid diet containing either 0%, 2%, 4% or 6.7% v/v ethanol, respectively. All the treatment groups received the same volume of an isocaloric diet as was consumed by the 35% EDC group. At birth, litters were culled to six and cross fostered to untreated surrogate mothers. Pups were sacrificed at 30 days of age and brains dissected into 8 regions. Each brain region was homogenized and divided into soluble and membrane bound fractions by centrifugation and digestion with deoxycholic acid. gamma-GTP activity was then measured. It was determined that the in utero exposure to alcohol produces an increase in brain gamma-GTP activity. The increase in gamma-GTP activity in some areas of brain is maintained at least until the animals are 30 days old. Alcohol treatment had no effect on the activity associated with the soluble form of enzyme. However, the activity associated with the membrane bound form of the enzyme was increased in several brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prenatal alcohol exposure on neonatal sleep-wake behaviour and adult alcohol consumption in rats

Our previous experiments showed that suppression of early postnatal active (REM) sleep increases alcohol intake in adult rats. To study the effects of prenatal alcohol exposure on neonatal sleep-wake behaviour and adult alcohol consumption pregnant rat dams were given 7% to 12% alcohol, 1% sucrose solution, or tap water as a sole liquid throughout gestation. Sleep-wake behaviour of the pups was studied at 6, 8, 12 and 15 days of age by using a movement sensitive mattress. The offspring who were exposed to alcohol in utero had significantly less active sleep and more wakefulness from total recording time than the controls. Their quiet state was also interrupted more often by waking episodes. At the age of 2 months voluntary alcohol intake of the rats exposed prenatally to alcohol was elevated compared to the controls. These findings suggest that early postnatal active sleep and the neurotransmitter systems regulating it may be the means by which in utero alcohol exposure affects adult alcohol drinking.