Alterations in neuronal development in the substantia nigra pars compacta following in utero ethanol exposure: immunohistochemical and Golgi studies

Prenatal Ethanol Exposure and Postnatal Environmental Intervention Alter Dopaminergic Neuron and Microglia Morphology in the Ventral Tegmental Area During Adulthood

BACKGROUND

Prenatal ethanol exposure (PE) impairs midbrain dopaminergic (DA) neuron function, which might contribute to various cognitive and behavioral deficits, including attention deficits and increased addiction risk, often observed in individuals with fetal alcohol spectrum disorders. Currently, the underlying mechanisms for PE-induced deficits are unclear. PE could lead to neuroinflammation by activating microglia, which play an important role in synaptic function. In the present study, we investigated PE effects on microglial activation and DA neuron density and morphology in the ventral tegmental area (VTA). Since postnatal environmental enrichment can reduce neuroinflammation and ameliorate several PE-induced behavioral deficits, we examined if a postnatal environmental intervention strategy using neonatal handling and postweaning complex housing could reverse PE effects on VTA DA neurons and microglia.

METHODS

Pregnant rats received 0 or 6 g/kg/d ethanol by 2 intragastric intubations on gestation days 8 to 20. After birth, rats were reared in the standard laboratory or enriched condition. Male adult rats (8 to 12 weeks old) were used for immunocytochemistry.

RESULTS

The results showed that PE decreased VTA DA neuron body size in standardly housed rats. Moreover, there was a significant decrease in numbers of VTA microglial branches and junctions in PE rats, suggesting morphological activation of microglia and possible neuroinflammation. The PE effects on microglia were normalized by postnatal environmental intervention, which also decreased the numbers of microglial branches and junctions in control animals, possibly via reduced stress.

CONCLUSIONS

Our findings show an association between PE-induced morphological activation of microglia and impaired DA neuron morphology in the VTA. Importantly, postnatal environmental intervention rescues possible PE-induced microglial activation. These data support that environmental intervention can be effective in ameliorating cognitive and behavioral deficits associated with VTA DA neuron dysfunctions, such as attention deficits and increased addiction risk.

Sex-specific effects of developmental alcohol exposure on cocaine-induced place preference in adulthood

Fetal Alcohol Syndrome (FAS) is associated with high rates of drug addiction in adulthood. One possible basis for increased drug use in this population is altered sensitivity to drug-associated contexts. This experiment utilized a rat model of FASD to examine behavioral and neural changes in the processing of drug cues in adulthood. Alcohol was given by intragastric intubation to pregnant rats throughout gestation and to rat pups during the early postnatal period (ET group). Controls consisted of a non-treated group (NC) and a pair-fed group given the intubation procedure without alcohol (IC). On postnatal day (PD) 90, rats from all treatment groups were given saline, 0.3mg/kg, 3.0mg/kg, or 10.0mg/kg cocaine pairings with a specific context in the conditioned place preference (CPP) paradigm. While control animals of both sexes showed cocaine CPP at the 3.0 and 10.0mg/kg doses, ET females also showed cocaine CPP at 0.3mg/kg. This was accompanied by a decrease in c-Fos/GAD₆₇ cells in the nucleus accumbens (NAc) shell and GAD₆₇-only cells in the NAc shell and PFC at this 0.3mg/kg dose. ET males failed to show cocaine CPP at the 3.0mg/kg dose. This was associated with an increase in c-Fos only-labeled cells in the NAc core and PFC at this 3.0mg/kg dose. These results suggest that developmental alcohol exposure has a sexually-dimorphic effect on cocaine's conditioning effects in adulthood and the NAc.

Prenatal Ethanol Exposure Persistently Alters Endocannabinoid Signaling and Endocannabinoid-Mediated Excitatory Synaptic Plasticity in Ventral Tegmental Area Dopamine Neurons

Prenatal ethanol exposure (PE) leads to increased addiction risk which could be mediated by enhanced excitatory synaptic strength in ventral tegmental area (VTA) dopamine (DA) neurons. Previous studies have shown that PE enhances excitatory synaptic strength by facilitating an anti-Hebbian form of long-term potentiation (LTP). In this study, we investigated the effect of PE on endocannabinoid-mediated long-term depression (eCB-LTD) in VTA DA neurons. Rats were exposed to moderate (3 g/kg/d) or high (6 g/kg/d) levels of ethanol during gestation. Whole-cell recordings were conducted in male offspring between 4 and 10 weeks old.We found that PE led to increased amphetamine self-administration. Both moderate and high levels of PE persistently reduced low-frequency stimulation-induced eCB-LTD. Furthermore, action potential-independent glutamate release was regulated by tonic eCB signaling in PE animals. Mechanistic studies for impaired eCB-LTD revealed that PE downregulated CB1 receptor function. Interestingly, eCB-LTD in PE animals was rescued by metabotropic glutamate receptor I activation, suggesting that PE did not impair the synthesis/release of eCBs. In contrast, eCB-LTD in PE animals was not rescued by increasing presynaptic activity, which actually led to LTP in PE animals, whereas LTD was still observed in controls. This result shows that the regulation of excitatory synaptic plasticity is fundamentally altered in PE animals. Together, PE leads to impaired eCB-LTD at the excitatory synapses of VTA DA neurons primarily due to CB1 receptor downregulation. This effect could contribute to enhanced LTP and the maintenance of augmented excitatory synaptic strength in VTA DA neurons and increased addiction risk after PE.SIGNIFICANCE STATEMENT Prenatal ethanol exposure (PE) is among many adverse developmental factors known to increase drug addiction risk. Increased excitatory synaptic strength in VTA DA neurons is a critical cellular mechanism for addiction risk. Our results show that PE persistently alters eCB signaling and impairs eCB-LTD at the excitatory synapses, an important synaptic plasticity that weakens synaptic strength. These effects combined with PE-induced anti-Hebbian long-term potentiation reported in a previous study could result in the maintenance of enhanced excitatory synaptic strength in VTA DA neurons, which in turn contributes to PE-induced increase in addiction risk. Our findings also suggest that restoring normal eCB signaling in VTA DA neurons could be a useful strategy for treating behavioral symptoms caused by PE.

Amphetamine sensitization and cross-sensitization with acute restraint stress: impact of prenatal alcohol exposure in male and female rats

RATIONALE

Individuals with fetal alcohol spectrum disorder (FASD) are at increased risk for substance use disorders (SUD). In typically developing individuals, susceptibility to SUD is associated with alterations in dopamine and hypothalamic-pituitary-adrenal (HPA) systems, and their interactions. Prenatal alcohol exposure (PAE) alters dopamine and HPA systems, yet effects of PAE on dopamine-HPA interactions are unknown. Amphetamine-stress cross-sensitization paradigms were utilized to investigate sensitivity of dopamine and stress (HPA) systems, and their interactions following PAE.

METHODS

Adult Sprague-Dawley offspring from PAE, pair-fed, and ad libitum-fed control groups were assigned to amphetamine-(1-2 mg/kg) or saline-treated conditions, with injections every other day for 15 days. Fourteen days later, all animals received an amphetamine challenge (1 mg/kg) and 5 days later, hormones were measured under basal or acute stress conditions. Amphetamine sensitization (augmented locomotion, days 1-29) and cross-sensitization with acute restraint stress (increased stress hormones, day 34) were assessed.

RESULTS

PAE rats exhibited a lower threshold for amphetamine sensitization compared to controls, suggesting enhanced sensitivity of dopaminergic systems to stimulant-induced changes. Cross-sensitization between amphetamine (dopamine) and stress (HPA hormone) systems was evident in PAE, but not in control rats. PAE males exhibited increased dopamine receptor expression (medial prefrontal cortex (mPFC)) compared to controls.

CONCLUSIONS

PAE alters induction and expression of sensitization/cross-sensitization, as reflected in locomotor, neural, and endocrine changes, in a manner consistent with increased sensitivity of dopamine and stress systems. These results provide insight into possible mechanisms that could underlie increased prevalence of SUD, as well as the impact of widely prescribed stimulant medications among adolescents with FASD.

Excitatory synaptic function and plasticity is persistently altered in ventral tegmental area dopamine neurons after prenatal ethanol exposure

Prenatal ethanol exposure (PE) is one of the developmental factors leading to increased addiction propensity (risk). However, the neuronal mechanisms underlying this effect remain unknown. We examined whether increased excitatory synaptic transmission in ventral tegmental area (VTA) dopamine (DA) neurons, which is associated with drug addiction, was impacted by PE. Pregnant rats were exposed to ethanol (0 or 6 g/kg/day) via intragastric intubation from gestational day 8-20. Amphetamine self-administration, whole-cell recordings, and electron microscopy were performed in male offspring between 2 and 12-week-old. The results showed enhanced amphetamine self-administration in PE animals. In PE animals, we observed a persistent augmentation in calcium-permeable AMPA receptor (CP-AMPAR) expression, indicated by increased rectification and reduced decay time of AMPAR-mediated excitatory postsynaptic currents (AMPAR-EPSCs), enhanced depression of AMPAR-EPSCs by NASPM (a selective CP-AMPAR antagonist), and increased GluA3 subunits in VTA DA neuron dendrites. Increased CP-AMPAR expression in PE animals led to enhanced excitatory synaptic strength and the induction of CP-AMPAR-dependent long-term potentiation (LTP), an anti-Hebbian form of LTP. These observations suggest that, in PE animals, increased excitatory synaptic strength in VTA DA neurons might be susceptible to further strengthening even in the absence of impulse flow. The PE-induced persistent increase in CP-AMPAR expression, the resulting enhancement in excitatory synaptic strength, and CP-AMPAR-dependent LTP are similar to effects observed after repeated exposure to drugs of abuse, conditions known to increase addiction risk. Therefore, these mechanisms could be important neuronal substrates underlying PE-induced enhancement in amphetamine self-administration and increased addiction risk in individuals with fetal alcohol spectrum disorders.

Fetal alcohol spectrum disorders and cognitive functions of young children

Fetal alcohol spectrum disorder (FASD) is one of the main causes of mental retardation worldwide. Nearly 1% of children in North America are affected from antenatal exposure to ethanol. Its economic burden in industrialized countries is increasing. It is estimated that, in the United States, 4.0 billion dollars are annually expended in the treatment and rehabilitation of these patients. As a pathologic entity, they present with a broad symptomatology. Fetal alcohol syndrome (FAS) is the most readily recognized clinical manifestation of these disorders. Various factors seem to contribute in the pathogenesis of FASD-related cognitive disorders. During the last 20 years, several potential pretranslational and posttranslational factors have been extensively studied in various experimental animal models. Research has specifically focused on several neurotransmitters, insulin resistance, alterations of the hypothalamic-pituitary-adrenal (HPA) axis, abnormal glycosylation of several proteins, oxidative stress, nutritional antioxidants, and various epigenetic factors. The purpose of the present review is to summarize the clinical manifestations of this disorder during childhood and adolescence and to summarize the possible pathophysiologic and epigenetic pathways that have been implicated in the pathophysiology of FASD.

Basal regulation of HPA and dopamine systems is altered differentially in males and females by prenatal alcohol exposure and chronic variable stress

Effects of prenatal alcohol exposure (PAE) on central nervous system function include an increased prevalence of mental health problems, including substance use disorders (SUD). The hypothalamic-pituitary-adrenal (HPA) and dopamine (DA) systems have overlapping neurocircuitries and are both implicated in SUD. PAE alters both HPA and dopaminergic activity and regulation, resulting in increased HPA tone and an overall reduction in tonic DA activity. However, effects of PAE on the interaction between HPA and DA systems have not been investigated. The present study examined PAE effects on basal regulation of central stress and DA systems in key brain regions where these systems intersect. Adult Sprague-Dawley male and female offspring from prenatal alcohol-exposed (PAE), pairfed (PF), and ad libitum-fed control (C) groups were subjected to chronic variable stress (CVS) or remained as a no stress (non-CVS) control group. Corticotropin releasing hormone (CRH) mRNA, as well as glucocorticoid and DA receptor (DA-R) expression were measured under basal conditions 24h following the end of CVS. We show, for the first time, that regulation of basal HPA and DA systems, and likely, HPA-DA interactions, are altered differentially in males and females by PAE and CVS. PAE augmented the typical attenuation in weight gain during CVS in males and caused increased weight loss in females. Increased basal corticosterone levels in control, but not PAE, females suggest that PAE alters the profile of basal hormone secretion throughout CVS. CVS downregulated basal CRH mRNA in the prefrontal cortex and throughout the bed nucleus of the stria terminalis (BNST) in PAE females but only in the posterior BNST of control females. PAE males and females exposed to CVS exhibited more widespread upregulation of basal mineralocorticoid receptor mRNA throughout the hippocampus, and an attenuated decrease in DA-R expression throughout the nucleus accumbens and striatum compared to CVS-exposed control males and females. Overall, these findings enhance our understanding of PAE effects on the cross-talk between HPA and DA systems, and provide insight into possible mechanisms underlying mental health problems that are related to stress and DA signaling, including SUD, which have a high prevalence among individuals with FASD.

Effects of ethanol exposure during early pregnancy in hyperactive, inattentive and impulsive behaviors and MeCP2 expression in rodent offspring

Prenatal exposure to alcohol has consistently been associated with adverse effects on neurodevelopment, which is collectively called fetal alcohol spectrum disorder (FASD). Increasing evidence suggest that prenatal exposure to alcohol increases the risk of developing attention deficit/hyperactivity disorder-like behavior in human. In this study, we investigated the behavioral effects of prenatal exposure to EtOH in offspring mice and rats focusing on hyperactivity and impulsivity. We also examined changes in dopamine transporter and MeCP2 expression, which may underlie as a key neurobiological and epigenetic determinant in FASD and hyperactive, inattentive and impulsive behaviors. Mouse or rat offspring born from dam exposed to alcohol during pregnancy (EtOH group) showed hyper locomotive activity, attention deficit and impulsivity. EtOH group also showed increased dopamine transporter and norepinephrine transporter level compared to control group in the prefrontal cortex and striatum. Prenatal exposure to EtOH also significantly decreased the expression of MeCP2 in both prefrontal cortex and striatum. These results suggest that prenatal exposure to EtOH induces hyperactive, inattentive and impulsive behaviors in rodent offspring that might be related to global epigenetic changes as well as aberration in catecholamine neurotransmitter transporter system.

New insights on neurobiological mechanisms underlying alcohol addiction

Alcohol dependence/addiction is mediated by complex neural mechanisms that involve multiple brain circuits and neuroadaptive changes in a variety of neurotransmitter and neuropeptide systems. Although recent studies have provided substantial information on the neurobiological mechanisms that drive alcohol drinking behavior, significant challenges remain in understanding how alcohol-induced neuroadaptations occur and how different neurocircuits and pathways cross-talk. This review article highlights recent progress in understanding neural mechanisms of alcohol addiction from the perspectives of the development and maintenance of alcohol dependence. It provides insights on cross talks of different mechanisms and reviews the latest studies on metaplasticity, structural plasticity, interface of reward and stress pathways, and cross-talk of different neural signaling systems involved in binge-like drinking and alcohol dependence.

Differentiation state-dependent effects of in vitro exposure to atrazine or its metabolite diaminochlorotriazine in a dopaminergic cell line

AIMS

This study sought to determine the impact of in vitro exposure to the herbicide atrazine (ATR) or its major mammalian metabolite diaminochlorotriazine (DACT) on dopaminergic cell differentiation.

MAIN METHODS

N27 dopaminergic cells were exposed for 24 or 48 h to ATR or DACT (12-300 μM) and their effects on cell viability, ATP levels, ADP:ATP ratio and differentiation markers, such as soma size and neurite outgrowth, were assessed.

KEY FINDINGS

Overall, intracellular ATP levels and soma size (decreased by ATR at ≥12 μM; 48 h) were the two parameters most sensitive to ATR exposure in undifferentiated and differentiating dopaminergic cells, respectively. At the morphological level, ATR, but not DACT, increased the percentage of morphologically abnormal undifferentiated N27 cells. On the other hand, exposure to DACT (300 μM; 48 h), but not ATR, increased the ADP:ATP ratio regardless of the differentiation state and it moderately disrupted thin neurite outgrowth. Only the highest concentration of ATR or DACT (300 μM) was cytotoxic after a longer exposure (48 h) and undifferentiated N27 cells were the least sensitive to the cytotoxic effects of ATR or DACT.

SIGNIFICANCE

Our results suggest that the energy perturbation and morphological disruption of dopaminergic neuronal differentiation induced by ATR and, to a lesser extent, DACT, may be associated with reported neurological deficits caused by developmental ATR exposure in rodents.

Chronic ethanol exposure changes dopamine D2 receptor splicing during retinoic acid-induced differentiation of human SH-SY5Y cells

There is evidence for ethanol-induced impairment of the dopaminergic system in the brain during development. The dopamine D2 receptor (DRD2) and the dopamine transporter (DAT) are decisively involved in dopaminergic signaling. Two splice variants of DRD2 are known, with the short one (DRD2s) representing the autoreceptor and the long one (DRD2l) the postsynaptic receptor. We searched for a model to investigate the impact of chronic ethanol exposure and withdrawal on the expression of these proteins during neuronal differentiation. RA-induced differentiation of human neuroblastoma SH-SY5Y cells seems to represent such a model. Our real-time RT-PCR, Western blot, and immunocytochemistry analyses of undifferentiated and RA-differentiated cells have demonstrated the enhanced expression of both splice variants of DRD2, with the short one being stronger enhanced than the long one under RA-treatment, and the DRD2 distribution on cell bodies and neurites under both conditions. In contrast, DAT was down-regulated by RA. The DAT is functional both in undifferentiated and RA-differentiated cells as demonstrated by [(3)H]dopamine uptake. Chronic ethanol exposure during differentiation for up to 4 weeks resulted in a delayed up-regulation of DRD2s. Ethanol withdrawal caused an increased expression of DRD2l and a normalization of DRD2s. Thus the DRD2s/DRD2l ratio was still disturbed. The dopamine level was increased by RA-differentiation compared to controls and was diminished under RA/ethanol treatment and ethanol withdrawal compared to RA-only treated cells. In conclusion, chronic ethanol exposure impairs differentiation-dependent adaptation of dopaminergic proteins, specifically of DRD2s. RA-differentiating SH-SY5Y cells are suited to study the impact of chronic ethanol exposure and withdrawal on expression of dopaminergic proteins during neuronal differentiation.

Timing of moderate level prenatal alcohol exposure influences gene expression of sensory processing behavior in rhesus monkeys

Sensory processing disorder, characterized by over- or under-responsivity to non-noxious environmental stimuli, is a common but poorly understood disorder. We examined the role of prenatal alcohol exposure, serotonin transporter gene polymorphic region variation (rh5-HTTLPR), and striatal dopamine (DA) function on behavioral measures of sensory responsivity to repeated non-noxious sensory stimuli in macaque monkeys. Results indicated that early gestation alcohol exposure induced behavioral under-responsivity to environmental stimuli in monkeys carrying the short (s) rh5-HTTLPR allele compared to both early-exposed monkeys homozygous for the long (l) allele and monkeys from middle-to-late exposed pregnancies and controls, regardless of genotype. Moreover, prenatal timing of alcohol exposure altered the relationship between sensory scores and DA D₂R availability. In early-exposed monkeys, a positive relationship was shown between sensory scores and DA D₂R availability, with low or blunted DA function associated with under-responsive sensory function. The opposite pattern was found for the middle-to-late gestation alcohol-exposed group. These findings raise questions about how the timing of prenatal perturbation and genotype contributes to effects on neural processing and possibly alters neural connections.

Ethanol inhibits muscarinic receptor-induced axonal growth in rat hippocampal neurons

BACKGROUND

In utero alcohol exposure can lead to fetal alcohol spectrum (FAS) disorders characterized by cognitive and behavioral deficits. In vivo and in vitro studies have shown that ethanol alters neuronal development. One mechanism through which ethanol has been shown to exert its effects is the perturbation of activated signaling cascades. The cholinergic agonist carbachol has been shown to induce axonal outgrowth through intracellular calcium mobilization, protein kinase C (PKC) activation, and ERK1/2 phosphorylation. This study investigated the effect of ethanol on the differentiation of rat hippocampal pyramidal neurons induced by carbachol as a possible mechanism involved in the developmental neurotoxicity of ethanol.

METHODS

Prenatal rat hippocampal pyramidal neurons were treated with ethanol (50 to 75 mM) in the presence or absence of carbachol for 24 hours. Neurite outgrowth was assessed spectrophotometrically; axonal length was measured in neurons fixed and immunolabeled with the neuron-specific betaIII tubulin antibody; cytotoxicity was analyzed using the thiazolyl blue tetrazolium bromide assay. The effect of ethanol on carbachol-stimulated intracellular calcium mobilization was assessed utilizing the fluorescent calcium probe, Fluo-3AM. The PepTag(R) assay for nonradioactive detection of PKC from Promega was used to measure PKC activity, and ERK1/2 activation was determined by densitometric analysis of Western blots probed for phospo-ERK1/2.

RESULTS

Ethanol treatment (50 to 75 mM) caused an inhibition of carbachol-induced axonal growth, without affecting neuronal viability. Neuron treatment for 15 minutes with ethanol did not inhibit the carbachol-stimulated rise in intracellular calcium, while inhibiting PKC activity at the highest tested concentration and ERK1/2 phosphorylation at both the concentrations used in this study. On the other hand, neuron treatment for 24 hours with ethanol significantly inhibited carbachol-induced increase in intracellular calcium.

CONCLUSIONS

Ethanol inhibited carbachol-induced neurite outgrowth by inhibiting PKC and ERK1/2 activation. These effects may be, in part, responsible for some of the cognitive deficits associated with in utero alcohol exposure.

The effect of acute and chronic exposure to ethanol on the developing encephalon: a review

OBJECTIVES: to compare the acute and chronic effects of ethanol on the neural development, by analysis of the ontogenetic neural structure of mammals. METHODS: searches were performed in the following electronic databases: MEDLINE, SciElo, PubMed, LILACS, CAPES periodical, and the Open Journal System. The descriptors used were: "chronic ethanol toxicity", "chronic alcohol toxicity", "acute ethanol toxicity", "acute alcohol", "neural ontogenic development", "neuronal migration disturbances", "neural structure". The following inclusion criteria were used: articles published between 2003 and 2007, some classic articles in the field and an important neuropsychology textbook. RESULTS: the analysis of papers revealed that, although several studies of the chronic effects of ethanol exposure on the mammalian nervous system have been conducted, only a few have investigated the acute effects of ethanol on specific days of gestation, and these studies have revealed important disorders relating to the cerebral tissue. CONCLUSIONS: it should be recommended that women refrain from the consumption of ethanol during gestational phase to protect the fetus' health. Furthermore, the acute consumption of ethanol by women nearing the eighth or ninth week of gestation has been shown to be potentially harmful to the nervous tissue of the fetus.

Combined exposure to nicotine and ethanol throughout full gestation results in enhanced acquisition of nicotine self-administration in young adult rat offspring

RATIONALE

Epidemiological evidence shows positive correlation between either maternal cigarette smoking or alcohol consumption on subsequent drug-taking behavior in offspring. However, the consequences of full gestational exposure to both drugs have not been studied experimentally despite concurrent use frequently reported among women of childbearing age. Such comorbid gestational drug exposure may increase susceptibility to acquiring cigarette smoking (i.e., nicotine self-administration), a major gateway drug.

OBJECTIVES

We developed a noninvasive rat model for exposure to both nicotine (2-6 mg kg(-1) day(-1)) and EtOH (4 g/kg gavage) that continued throughout pregnancy and postnatal (P) days 2-12, the rodent equivalent of the human third trimester, a critical brain developmental period. Offspring with this full gestational exposure to both drugs (Nic+EtOH) were compared to controls: nicotine alone, EtOH alone, pair-fed (comparable nutrition and handling), and ad libitum chow-fed. At P60-90, offspring had unlimited chronic access to acquire i.v. nicotine self-administration.

RESULTS

There were no differences in gender ratio, stillbirths, birth weights, righting reflex, eye opening age, or weight gain. However, Nic+EtOH offspring of both genders acquired nicotine self-administration (15 or 30 microg kg(-1) injection(-1)) more rapidly, at a higher percentage, and at a higher level than offspring in the other cohorts.

CONCLUSION

Full gestational Nic+EtOH exposure produced no overt alterations in standard postnatal measures but resulted in an enhanced acquisition of nicotine self-administration in young adult offspring.

Effects of Prenatal Ethanol Exposure on the Excitability of Ventral Tegmental Area Dopamine Neurons in Vitro

Prenatal ethanol exposure leads to a persistent reduction in the number of spontaneously active dopaminergic (DA) neurons (DA neuron population activity) in the ventral tegmental area (VTA) in developing and adult animals. This effect might contribute to the dysfunction of the mesolimbic/cortical DA system and attention problems in children with fetal alcohol spectrum disorders. To characterize the underlying cellular mechanism for prenatal ethanol exposure-induced reduction in VTA DA neuron population activity, we used the whole-cell patch-clamp technique to study the membrane properties of putative VTA DA neurons in brain slices in 2- to 3-week-old control and prenatal ethanol-exposed animals. The results show that prenatal ethanol exposure did not impair the spontaneous pacemaker activity in putative VTA DA neurons but reduced the frequency of evoked action potentials. In addition, prenatal ethanol exposure led to a reduction in hyperpolarization-induced cation current (I(h)) and an up-regulation of somatodendritic DA autoreceptors. The above prenatal ethanol exposure-induced changes could decrease the excitability of VTA DA neurons. However, they do not seem to play a role in reduced VTA DA neuron population activity in vivo, an effect thought to be mediated by excessive excitation leading to depolarization inactivation. Taken together, the above results indicate that prenatal ethanol exposure-induced reduction in VTA DA neuron population activity in vivo is not caused by changes in the intrinsic pacemaker activity or other membrane properties and could instead be caused by altered inputs to VTA DA neurons.

Different adaptations in ventral tegmental area dopamine neurons in control and ethanol exposed rats after methylphenidate treatment

BACKGROUND

Methylphenidate (MPH) is a psychostimulant effective in treating attention-deficit/hyperactivity disorder (ADHD). Repeated MPH treatment may increase substance abuse risk because of adaptations in dopaminergic (DA) function associated with sensitization to subsequent stimulant exposure. However, this possibility is based on observations in normal animals and may not apply to animals with attention problems linked to compromised DA function such as prenatal ethanol exposed (PE) animals.

METHODS

The electrical activity of ventral tegmental area (VTA) DA neurons was studied after the cessation of repeated MPH treatment at a threshold dose (1 mg/kg/day for 3 weeks) in PE and control rats.

RESULTS

In control rats, there was a continuous increase in VTA DA neuron excitability post-MPH treatment, characterized by a transient increase in population activity (1 day posttreatment) followed by decreased population activity (30-60 days posttreatment) in most of the animals due to depolarization inactivation. In PE rats, MPH treatment decreased the excessive excitability of VTA DA neurons and resulted in prolonged normalization in the population activity (1-60 days posttreatment). These changes were not mediated by altered sensitivity of somatodendritic DA autoreceptors.

CONCLUSIONS

Repeated MPH treatment produced distinctly different effects on VTA DA neuron activity in control and PE animals. These results suggest that repeated MPH treatment for ADHD may not lead to increased substance abuse risk in special populations such as individuals with fetal alcohol spectrum disorder.

Moderate-level prenatal alcohol exposure alters striatal dopamine system function in rhesus monkeys

BACKGROUND

Moderate prenatal alcohol exposure can cause impairments even in the absence of gross morphological defects associated with fetal alcohol syndrome. The basal ganglia, which include the dopamine-rich striatum, are sensitive to fetal alcohol-induced injury. In this study, we manipulated the timing of moderate-level alcohol exposure and compared the risk of adverse effects on striatal dopamine (DA) system function in rhesus monkeys.

METHODS

Thirty-five young adult rhesus monkeys (Macaca mulatta) from four groups of females were assessed: (1) an early alcohol-exposed group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 0 through 50; (2) a middle-to-late gestation alcohol-exposed group (n=7), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 50 through 135; (3) a continuous-exposure group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on days 0 through 135; and (4) controls (n=10), in which mothers voluntarily consumed an isocaloric control solution on gestational days 0 through 50, 50 through 135, or 0 through 135. We studied striatal DA system function by positron emission tomography in separate scans for trapping of [(18)F]fallypride and 6-[(18)F]fluoro-m-tyrosine to assess striatal DA D2 receptor (D2R) binding and DA synthesis, respectively, via dopadecarboxylase activity.

RESULTS

Moderate-level alcohol exposure during early gestation and continuous exposure throughout gestation (early + middle-to-late exposure) reduced the striatal D2R binding to DA synthesis ratio, whereas middle-to-late alcohol gestation exposure increased the striatal D2R binding to DA synthesis ratio. The continuous-exposure group showed the largest effect. Moreover, the D2R binding/DA synthesis ratio was related to neonatal neurobehavior measures in control monkeys, but these relationships were disrupted in the fetal alcohol-exposed monkeys.

CONCLUSION

These results suggest that the vulnerability of the DA system to the effects of moderate doses of alcohol during gestation depend on the timing of the alcohol exposure. Early-gestation moderate alcohol exposure resulted in a reduction or blunting of dopaminergic function in adulthood, whereas middle to late exposure (without early exposure) either induced the opposite pattern or heightened dopaminergic function. Continuously exposed monkeys showed the largest effect, suggesting that the sooner women stop drinking, the better it is for the fetus.

Prenatal ethanol preferentially enhances reactivity of the dopamine D1 but not D2 or D3 receptors in offspring

Reports of prenatal ethanol (ETOH) effects on the dopamine system are inconsistent. In an attempt to clarify this issue, dams were given 35% ethanol-derived calories as the sole nutrient source in a liquid diet from the 10th through the 20th day of gestation (ETOH). Controls were pair-fed (PF) an isocaloric liquid diet or given ad libitum access to laboratory chow (LC). Prenatal exposure to both liquid diets reduced body weight of offspring relative to LC controls, more so for ETOH than for PF exposure. Prenatal ETOH also decreased litter size and viability, relative to both LC and PF control groups. On postnatal days 21-23, male and female offspring were given an injection of saline vehicle or one of eight specific dopamine receptor agonists or antagonists. Immediately after injection subjects were placed in individual observation cages, and over the following 30 min, eight behaviors (square entries, grooming, rearing, circling, sniffing, yawning, head and oral movements) were observed and quantified. No prenatal treatment effects on drug-induced behaviors were observed for dopamine D2 (Apomorphine, DPAT or Quinpirole) or D3 (PD 152255, Nafadotride, Apo or Quin effects on yawning) receptor agonists or antagonists, or for the vehicle control. In contrast, prenatal treatment effects were seen with drugs affecting the dopamine D1 receptor. Both D1 agonists (SKF 38393) and antagonists (SCH 23390 and high doses of spiperone) altered behaviors, especially oral and sniffing behaviors, in a manner which suggested enhanced dopamine D1 drug sensitivity in both ETOH and PF offspring relative to LC controls. These results suggest that at this age, both sexes experience a prenatal undernutrition-linked increase in the behavioral response to dopamine D1 agonists and antagonists, which can be intensified by gestational exposure to alcohol.

Disruption of cholesterol homeostasis in the developing brain as a potential mechanism contributing to the developmental neurotoxicity of ethanol: an hypothesis

While excess cholesterol may have deleterious consequences, as in the case of atherosclerosis, too little cholesterol may endanger the development of the brain. Different degrees of mental retardation are often observed in inborn errors of cholesterol synthesis, such as the Smith-Lemli-Opitz syndrome or in maternal phenylketonuria, where the metabolite of accumulating phenylalanine, phenylacetate, is an inhibitor of cholesterol synthesis. Lack of cholesterol during brain development as a consequence of these genetic defects leads to severe brain damage, microencephaly and mental retardation, which are also hallmarks of the fetal alcohol syndrome (FAS). The brain relies on the in situ synthesis of cholesterol, which occurs mostly in astrocytes. Astrocyte-produced cholesterol is utilized for cell proliferation, or is released, via astrocyte-secreted high density lipoprotein-like particles containing apolipoprotein E, outside the cell, where it is taken up and utilized by neurons for dendrite outgrowth and to form synapses. We propose the hypothesis that ethanol may disrupt cholesterol homeostasis during brain development, and that this effect may be responsible, at least in part, for the central nervous system dysfunctions observed in the FAS, which include altered astrocyte proliferation, neuronal death and diminished synaptic contacts.

Ethanol withdrawal influences survival and morphology of developing rat hippocampal neurons in vitro

BACKGROUND

Previous studies in this laboratory have shown that, like their counterparts in vivo, fetal rat hippocampal pyramidal neurons in culture develop abnormally small dendritic arbors when exposed to ethanol. This study asked whether ethanol's inhibitory effects on dendritic development differ when the duration of ethanol exposure and timing of withdrawal are varied to correspond with early versus later stages of development and whether ethanol withdrawal influences survival of these neurons.

METHODS

We compared neurons exposed continuously for 6 or 14 days to ethanol (70 mM) with neurons transferred from ethanol-containing medium to control medium either 1 day after adding ethanol (before dendrites elongated) or 6 days after adding ethanol (after dendrites began elongating). We then performed morphometric and cell density analyses at 6 and 14 days using digital images of neurons immunostained with microtubule-associated protein 2 (MAP2) to visualize dendrites.

RESULTS

Continuous exposure to ethanol decreased the length and number of dendrites formed but had no effect on neuron survival compared with controls without ethanol. Dendritic length was less inhibited when ethanol was withdrawn after 1 day, but the number of dendrites per cell was unchanged compared with neurons continuously exposed to ethanol. Withdrawal from ethanol at 1 day slightly enhanced the survival of neurons assessed at 14 days compared with neurons in control medium and with neurons exposed continuously to ethanol. In contrast, withdrawal from ethanol at 6 days severely decreased the number of neurons at 14 days.

CONCLUSIONS

These results suggest that dendrites can achieve normal length when ethanol exposure is limited to only 1 day and withdrawal occurs before dendrites begin elongating. However, a persistent reduction in dendrite number results in smaller overall dendritic arbor size. Although continuous exposure to ethanol has little effect on neuron survival in these cultures, and exposure limited to 1 day followed by withdrawal can be neuroprotective against cell death associated with increased time in culture, longer exposure before withdrawal can trigger cell death.

Methylphenidate Restores Ventral Tegmental Area Dopamine Neuron Activity in Prenatal Ethanol-Exposed Rats by Augmenting Dopamine Neurotransmission

Altered neurotransmission in the mesolimbic dopamine (DA) system has been suggested to be the underlying cause of attention problems commonly observed in children with fetal alcohol spectrum disorder (FASD). Methylphenidate is effective in treating attention problems in children with FASD. However, the underlying mechanism is currently unknown. We have shown previously that reduced ventral tegmental area (VTA) DA neuron activity in prenatal ethanol-exposed animals can be normalized by DA agonist treatment. In the present study, we investigated the possibility that similar mechanism mediates the effect of methylphenidate using the in vivo extracellular single-unit recording technique in anesthetized animals. We observed that reduced VTA DA neuron activity in prenatal ethanol-exposed animals was normalized by methylphenidate. The effect of methylphenidate was mediated by increased extracellular levels of DA instead of norepinephrine because this effect was not altered by the coadministration of prazosin, an alpha(1) receptor antagonist, and was mimicked by the application of DA transporter blockers, nomifensine and 1-2(-[bis(4-flurophenyl)methoxy]ethyl)-4-(3-phenyl)piperazine dihydrochloride (GBR 12909). These observations support our hypothesis that depolarization inactivation is the cause of prenatal ethanol exposure-induced reduction in VTA DA neuron activity. We speculate that methylphenidate normalized the activity of VTA DA neurons by increasing extracellular DA levels in the VTA and the activation of somatodendritic DA autoreceptors. As a result, the depolarization inactivation was removed by hyperpolarization. The normalized VTA DA neuron activity in prenatal ethanol-exposed animals may contribute to a restoration of DA neurotransmission and the therapeutic effect of methylphenidate in attention problems in children with FASD.

Prenatal ethanol exposure alters the postnatal development of the spontaneous electrical activity of dopamine neurons in the ventral tegmental area

Prenatal ethanol exposure causes a persistent reduction in the spontaneous electrical activity of dopamine (DA) neurons in the ventral tegmental area (VTA) in adult animals. Because DA neuron activity matures into adult pattern during postnatal development, it is possible that reduced activity in VTA DA neurons after prenatal ethanol exposure is caused by impaired postnatal development. This possibility was investigated in the present study using the in vivo extracellular single-unit recording and brain stimulation techniques. The results show an age-dependent decrease in the number of spontaneously active VTA DA neurons from 2 to 4 weeks of age in both the control and prenatal ethanol-exposed animals. In ethanol-exposed animals, the age-dependent decrease was more prominent after 3 weeks of age, resulting in lower numbers of spontaneously active VTA DA neurons in 4-week-old and adult animals. In both the control and ethanol-exposed animals, there were age-dependent increases in the firing rates and burst firing activity of VTA DA neurons after 2 weeks of age. Ethanol exposure led to slightly lower firing rates in 4-week-old and adult animals and did not impact the burst firing pattern in any age groups. There were no changes in axon conduction velocity and antidromic spike characteristics of VTA DA neurons. These results indicate that reduced activity of VTA DA neurons during adulthood after prenatal ethanol exposure does not begin prenatally. Instead, it is a result of impaired postnatal development manifested only when animals reach 4 weeks of age. These results suggest that early intervention may be an effective treatment strategy for attention deficit/hyperactivity disorder, a behavioral dysfunction related to the abnormalities of DA systems and often observed in children with fetal alcohol spectrum disorder.

Neurodevelopmental liabilities in alcohol dependence: central serotonin and dopamine dysfunction

Alcoholism is a complex disorder with symptoms ranging from abuse to dependence, often comorbid with depression, antisocial personality, or anxiety. Neurodevelopmental causes of the disorder are unknown but inferences are possible from current knowledge. Neurobiological studies implicate multiple brain changes, which may be characterized as premorbid or morbid. These studies have also examined specific aspects of the alcohol dependence syndrome, including alcohol reinforcement and craving. Here, we review the evidence for vulnerability factors in alcohol dependence, with an emphasis on central serotonin (5-HT) and dopamine (DA). Serotonin dysfunction likely contributes to the development of alcoholism since studies of alcohol-preferring rodents show decreased 5-HT function on many measures. We have shown that serotonin-enhancing drugs reduce consumption and craving in mild to moderate alcoholics, yet similar studies in severely dependent individuals remain inconclusive. Studies indicate that serotonin dysfunction may contribute to the development of dependence via impaired impulse control and/or mood regulation. The mesocorticolimbic dopamine pathway represents another important pathophysiological target in alcoholism. Differences in D(2) receptor density, dopamine sensitivity, and gene expression have been linked to consumption, reinforcement, craving, and relapse. However, while DA agonists reduce self-administration in animals, we found no effect in humans with long-acting bromocriptine, a D(2) agonist. Dopamine may contribute differentially to the development of dependence via its effects on alcohol wanting, reinforcement, and reward memory. Although animal experiments show consistent roles for serotonin and dopamine in alcohol dependence, human studies are not always concordant. Such discrepancies highlight the complexity of dependence-related behaviors in humans and of identifying vulnerabilities to alcoholism.

Prenatal alcohol exposure decreases the number of nitric oxide synthase positive neurons in rat superior colliculus and periaqueductal gray

Because nitric oxide (NO) is involved in the development and refinement of axonal projections and synapses, it is of interest to know if developmental alcohol exposures affect NO producing neurons. Pregnant rats were fed artificial liquid diet throughout gestation as the only fluid or caloric source. The diet for experimental dams contained ethanol (6.7% v/v) while the pair-fed diet for control dams contained isocaloric maltose-dextrin instead of ethanol. This ethanol diet regime is known to produce peak blood alcohol concentrations of approximately 140 mg%. Cells stained histochemically for nitric oxide synthase (NOS) were counted at postnatal day 15 (P15) and 35 (P35) in cross-sections of the stratum griseum superficiale (SGS) of the superior colliculus (SC) and in the dorsolateral column of the periaqueductal gray (dlPAG). Compared to control tissues, alcohol caused the following effects: In the SC, the areal density of NOS+ neurons was decreased 24% at P15 but a similar decrease in means at P35 was not statistically significant (P=0.10); soma size was unaffected at either P15 or P35. In the dlPAG, both the areal density and the total number of NOS+ neurons per section were unaffected at P15 but were decreased at P35 (33% and 37% decreases); soma size was unaffected at either P15 or P35. The decrease in NOS+ neurons in the SC at P15 could be expected to have a negative impact on the refinement of neuronal connections while the decreases in NOS+ neurons in the dlPAG at P35 likely represent more permanent effects that could alter the function of that nucleus.

Ethanol inhibits development of dendrites and synapses in rat hippocampal pyramidal neuron cultures

Evidence suggests that some neuropathologic manifestations of Fetal Alcohol Syndrome (FAS) result from the disruption of neuromorphogenesis and synapse formation in the hippocampus. Prior research in this laboratory has shown that ethanol in the medium during the first 24 h in culture increases the number of minor processes (the precursors of axons and dendrites) and accelerates the rate at which axons are formed in low-density cultures of embryonic rat hippocampal neurons. The current study examined the effects of ethanol on the subsequent development of dendrites and synapses in these cultures. Quantitative morphometric analysis utilized double-immunofluorescent staining for MAP2 and synapsin I to visualize dendrites and synaptic specializations, respectively. Six days of ethanol (200, 400 or 600 mg/dl) in the medium, beginning at the time of plating, resulted in decreases in total dendritic length per cell, dendrite number per cell, length of individual dendrites and synapse number per innervated dendrite but had no effect on cell survival. The decrease in synapse number was correlated with dendrite length, suggesting that ethanol's effects on synapse number are secondary to its effects on dendritogenesis. Taken together with our previous findings, these results are the first to demonstrate that ethanol has differential effects on axonal and dendritic growth in a culture model of neurons that are vulnerable to ethanol-induced cytoarchitectural abnormalities during development in vivo.

Effects of chronic ethanol consumption on SER of Purkinje neurons in old F344 rats

The purpose of this study was to determine whether the observed swelling of smooth endoplasmic reticulum (SER) profiles in Purkinje dendrites in our old ethanol-fed F344 rats: (1) represented measurable dilatation, (2) was present in dendritic shafts and spines, and (3) was reversed following recovery from ethanol. Of the 45 rats in 3 treatment groups (chow-fed, pair-fed, and ethanol-fed), 30 rats were euthanized after 40 weeks, and 15 were maintained on rat chow for an additional 20-week recovery period. Electron microscopy of cerebellar preparations was used to analyze morphological alterations in SER profile size within the dendritic shafts and spines of Purkinje neurons. Results showed significant SER dilatation following 40 weeks of ethanol consumption, which disappeared after ethanol withdrawal.

Loss of nicotine-induced effects on locomotor activity in fetal alcohol-exposed rats

Previous evidence from our laboratory showed that systemic injection of nicotine enhanced attention and memory in control rats, but not fetal alcohol-exposed (FAE) rats. The present study examined the effects of nicotine on two measures of locomotor activity in FAE rats. Subjects were 2-month-old male offspring of Sprague-Dawley rats fed a 35% ethanol-derived caloric diet, a pair-fed sucrose diet, or a chow-fed diet during the last 2 weeks of gestation. The two experiments examined the effects of intraperitoneal injection of saline or nicotine (0.25 or 0.75 mg/kg) on rearing in an operant chamber and locomotor activity in an open field for 60 min. The high dose of nicotine produced a decrease in rearing in the first 10-min period, followed by a later increase in rearing in the pair-fed and chow-fed groups, but not the FAE group. Nicotine also produced an elevation of locomotor activity in the open field in only the two control groups. These findings provide additional evidence that FAE rats show less behavioral responsiveness to nicotine.

Fetal alcohol-exposed rats exhibit differential response to cholinergic drugs on a delay-dependent memory task

Fetal alcohol exposure in human and rodents produces a number of cognitive deficits including impairments in learning and memory. Recent evidence in our laboratory has shown that fetal alcohol-exposed (FAE) rats respond differently to systemic administration of cholinergic drugs when tested for vigilance and locomotor activity. The present study examined the effects of muscarinic and nicotinic agonists and antagonists on memory performance in a delayed alternation task. Subjects were male offspring of Sprague-Dawley rats fed a 35% ethanol-derived caloric diet, pair-fed with sucrose, or chow-fed with lab chow during the last 2 weeks of gestation. Rats (3 months old) were food-deprived prior to training in the T-maze. Rats were first trained in the alternation task at no delay for five sessions. Rats were then trained at longer delays (20, 60, 180 s) until all groups showed similar performance for two consecutive sessions. Each animal was then tested following systemic injections of the cholinergic antagonists scopolamine and mecamylamine (60-s delay) and the cholinergic agonists pilocarpine and nicotine (180-s delay). Rats received saline injections on alternate days of testing. The results revealed that FAE rats exhibited no impairments in alternation performance at the no delay and 20-s delay, but showed impairments on both the 60- and 180-s delays during the initial sessions. However, with additional training, FAE rats showed performance similar to that of control groups at these delays. Following both pilocarpine and nicotine injections, control groups, but not the FAE group, showed significant memory enhancement in the alternation task. Following scopolamine injections, the FAE rats showed a significant impairment, while control groups showed a nonsignificant decrease in performance. All three groups showed impairments in the alternation task following administration of mecamylamine compared to saline treatment. These findings suggest that alterations in the cholinergic system in FAE rats may underlie some of the cognitive deficits observed with prenatal alcohol exposure.

Neurotrophic factors BDNF and GDNF protect embryonic chick spinal cord motoneurons from ethanol neurotoxicity in vivo

Maternal consumption of ethanol is widely recognized as a leading cause of mental and physical deficits. Many populations of the central nervous system are affected by the teratogenic effects of ethanol. Neurotrophic factors (NTFs) have been shown to protect against ethanol neurotoxicity in culture, although there have been no demonstrations of such protection in vivo, in specific neuronal populations. Previous studies have demonstrated that ethanol is toxic to developing chick embryo motoneurons when administered from embryonic day 10 (E10) to E15. NTFs such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) have been shown to support developing spinal cord motoneurons, and when exogenously applied, decrease naturally occurring cell death, and protect against axotomy. The concurrent delivery of BDNF or GDNF with ethanol to the embryonic chick from E10 to E15 was designed to examine the capacity of these NTFs to provide in vivo neuroprotection for this ethanol-sensitive motoneuron population. Analysis of motoneuron numbers indicated that both BDNF and GDNF provided protection to developing spinal cord motoneurons from ethanol toxicity, restoring motoneuron numbers to control levels. This study represents the first demonstration of in vivo neuroprotection from ethanol toxicity with respect to specific neuronal populations.

Fetal alcohol exposure and temporal vulnerability regional differences in alcohol-induced microencephaly as a function of the timing of binge-like alcohol exposure during rat brain development

In humans, microcephaly (small head for body size) is a common feature of fetal alcohol syndrome. An analogous measure, termed microencephaly (small brain for body size), can be used for evaluating the detrimental effects of the differential timing of alcohol exposure on brain development in animal model systems. Timed-pregnant rats were exposed to binge-like alcohol during either the first 10 days (first trimester equivalent) or second 10 days of gestation (second trimester equivalent), or the combination of first and second trimesters equivalent for prenatal treatments. Offspring from some of the animals exposed to alcohol during the combined first and second trimesters equivalent were raised artificially from postnatal day (P) 4 through P9 (part of the third trimester equivalent), and also received binge-like alcohol during this period, producing animals that were exposed to alcohol during all three trimesters equivalent. Offspring from untreated dams were also raised artificially and received alcohol only from P4 to P9, thus creating animals that were exposed to alcohol only during part of the third trimester equivalent. All pups were perfused on P10. Appropriate controls (nutritional and normally reared) were used for every alcohol treatment combination. Peak blood alcohol concentrations were not different among the treatment groups for a given sampling time. Significant somatic growth deficits occurred in offspring exposed to alcohol for the equivalent of all three trimesters, compared with offspring exposed to alcohol during other periods. Brain growth in offspring also was significantly affected by the timing of alcohol exposure. The whole brain, forebrain, and cerebellum to body weight ratios of pups exposed to alcohol during the third trimester had more significant brain growth deficits than pups in groups exposed to alcohol during other times of brain development. Although alcohol exposure during the third trimester had a significant detrimental impact on overall brain growth, significant differences in temporal vulnerability were also found for the brainstem to body weight ratios. Offspring of dams exposed to alcohol during the first trimester had the same magnitude of deficit as those exposed to alcohol during the third trimester, and those two groups were significantly deficient compared with the groups exposed to alcohol at other times, suggesting some differential vulnerability of this region to alcohol-induced injury at different times of development. This study is the first thorough examination of microencephaly and gross regional vulnerability of the developing brain as related to temporal factors of alcohol exposure in an animal model system, and the results support and expand on the findings of the available clinical literature. Furthermore, our results substantiate claims that the cessation of alcohol before the third trimester can lessen the severity of some alcohol-related birth deficits.

Ethanol consumption following recovery from unilateral damage to the forelimb area of the sensorimotor cortex: reinstatement of deficits and prevention of dendritic pruning

Unilateral injury to the forelimb-representation area of the sensorimotor cortex (FL-SMC) in adult rats results in use-dependent proliferation of dendritic processes, followed by partial pruning, of layer V pyramidal neurons of the contralateral homotopic cortex. In development, 'exuberant' growth of neurons is often followed by pruning, a process that has been associated with a glutamatergic-NMDA receptor mechanism. A related mechanism may play a role in injury-related pruning of dendrites in adults. The N-methyl-D-aspartate (NMDA) receptor antagonist MK801, administered throughout the pruning phase to adult animals with FL-SMC lesions, prevents dendritic pruning and disrupts behavioral recovery. Ethanol (ETOH) also acts as an NMDA receptor antagonist. It has been shown to reduce NMDA-active ion currents, inhibit NMDA-evoked electrophysiological responses, and decrease glutamate-binding in the hippocampus and cortex. ETOH also affects neuromorphology in the developing and adult cerebellum, hippocampus, and cortex. Ethanol's involvement with NMDA receptor function and its influence on dendritic morphology led us to examine its effect on dendritic pruning and behavioral recovery following unilateral FL-SMC lesions. Lesioned animals were exposed to moderate doses of ethanol in a liquid diet only during the period of dendritic pruning. As with MK801, ETOH prevented pruning and reinstated chronic behavioral asymmetries.

Ethanol influences on the chick embryo spinal cord motor system. II. Effects of neuromuscular blockade and period of exposure

The study described below was performed as a continuation of a previous study in which we found reduced motoneuron number in lumbar spinal cord of the chick embryo following chronic ethanol administration from embryonic day 4 (E4) to E11. We sought to determine whether this reduction was due to primary ethanol toxicity or to enhancement of naturally occurring cell death (NOCD) and to determine whether administration of ethanol at a later period of development could also reduce motoneuron number. Earlier studies have shown that curare suspends NOCD in the chick embryo. By administering both ethanol and curare to these embryos from E4 to E11 and examining the lumbar spinal cord on E12, we determined that ethanol was directly toxic to motoneurons and reduced motoneuron number in the absence of NOCD. By administering ethanol from E10 to E15 and examining the lumbar spinal cord on E16, we determined that ethanol can reduce motoneuron number without altering spinal cord length during more than one stage of chick embryo development, and that ethanol toxicity is not dependent on NOCD. In addition, we demonstrated that ethanol does not affect the neurotrophic content of chick muscle when it is administered from E10 to E15.

Hearing, speech, language, and vestibular disorders in the fetal alcohol syndrome: a literature review

Fetal alcohol syndrome (FAS) is characterized in part by mental impairment, as well as craniofacial and ocular anomalies. These conditions are traditionally associated with childhood hearing disorders, because they all have a common embryonic origin in malformations of the first and second branchial arches, and have similar critical periods of vulnerability to toxic insult. A review of human and animal research indicates that there are four types of hearing disorders associated with FAS. These are: (1) a developmental delay in auditory maturation, (2) sensorineural hearing loss, (3) intermittent conductive hearing loss due to recurrent serous otitis media, and (4) central hearing loss. The auditory and vestibular systems share the same peripheral apparatuses (the inner ear and eighth cranial nerve) and are embryologically and structurally similar. Consequently, vestibular disorders in FAS children might be expected. The evidence for vestibular dysfunction in FAS is ambiguous, however. Like other syndromes associated with craniofacial anomalies, hearing disorders, and mental impairment, FAS is also characterized by a high prevalence of speech and language pathology. Hearing disorders are a form of sensory deprivation. If present during early childhood, they can result in permanent hearing, language, and mental impairment. Early identification and intervention to treat hearing, language, and speech disorders could therefore result in improved outcome for the FAS child. Specific recommendations are made for intervention and future research.

Effects of acute prenatal ethanol exposure on Bergmann glia cells early postnatal development

The effects of acute ethanol exposure during the prenatal phase of Bergmann glia cell (Bgc) generation were evaluated in three postnatal days. Ethanol exposed rats showed Bgc with reduced soma size, decreased number and width of their fibers, and increased fiber length, when compared with control animals. These differences, however, were significant at postnatal day 12. Our results demonstrate that acute, prenatal exposure to ethanol during critical stages of brain development disrupts Bgc early postnatal development.

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.

Ethanol exposure alters the development of serotonergic neurons in chick spinal cord

Exposure to ethanol is known to alter the development of the serotonergic system. However, previous studies have examined large populations of cells and have not determined the effects of ethanol on individual serotonergic neurons. In the present study, the effects of various concentrations of ethanol on the development of single serotonergic neurons in the chick embryo spinal cord were determined using immunohistochemical techniques. Between embryonic day 7 (E7) and E14, ethanol administrations produced in ovo alcohol concentrations of: a) low dose, 30-60 mg/dl, b) medium dose, 150-200 mg/dl or c) high dose, 240-300 mg/dl. In animals exposed to the medium and high ethanol doses, the normal developmental increase in cross-sectional area of the somata was not observed. At all stages examined, the numbers of primary and nonprimary processes were significantly lower in ethanol-treated groups compared to controls. These data indicate that ethanol exposure induces dose-dependent alterations in the development of identified spinal cord neurons. The ethanol-induced changes may be involved in the motor dysfunction observed after embryonic ethanol exposure.

Prenatal alcohol exposure and the effects of environmental enrichment on hippocampal dendritic spine density

The effects of environmental enrichment on synaptic spine density in hippocampal area CAI were examined in rats exposed prenatally to alcohol. Pregnant dams were given ethanol via intragastric intubation (6 g/kg/day) from gestational days 8 through 19, or given isocaloric sucrose. An untreated control group was also used. After weaning, offspring from the three groups were then reared for 10 weeks in either isolated (caged alone, not handled) or enriched (group housed with "toys," handled) conditions. Animals were then sacrificed, the brains Golgi impregnated, and CAI pyramidal cell apical and basilar spine densities quantified. Among isolated animals there were no significant differences between control and alcohol-exposed groups. In general, environmental enrichment increased apical or basilar spine densities in untreated and sucrose controls. However, in prenatal alcohol-exposed animals, environmental enrichment did not increase spine densities. Because the environmental enrichment acted postnatally, these findings suggest that the effects of prenatal alcohol exposure included decreased neural plasticity enduring into early adulthood. Such a reduction in neuroanatomical plasticity in hippocampus may be associated with cognitive impairments found following prenatal alcohol exposure.

Influence of prenatal ethanol exposure on cholinergic development in the rat striatum

This study investigated the influence of ethanol exposure throughout gestation on cholinergic development within the rat striatal region. Pregnant Long-Evans rats were maintained on three diets throughout gestation: A liquid diet in which ethanol accounted for 35-39% of the total calories, a similar diet with the isocaloric substitution of sucrose for ethanol, and a lab chow control diet. At postnatal days 14 and 60 (P14 and P60), the striatal regions of the offspring were analyzed for the number of cholinergic neurons, via choline acetyltransferase (ChAT) immunostaining. The area of the striatum was also measured in these animals. At P14, P21, and P60, ChAT activity was assessed in the same region. These analyses revealed a significant increase in the number of cholinergic striatal neurons at P14 in the animals which had been exposed prenatally to ethanol. This increase was transient, however, with equal numbers of ChAT-positive cells found in all three groups by adulthood (P60). The brain weights of the ethanol-exposed animals were significantly reduced at P14 and P21, but were comparable to controls by P60. There were no significant differences in the striatal area or the overall volume of the region assessed, however, at either P14 or P60. Although there were some increases in ChAT activity across the ages viewed (most notably between P14 and P21), there were no effects of diet on ChAT activity at any age assessed. It is proposed that the increased numbers of cholinergic neurons could be a function of errors in migration, enhanced neurogenesis, diminished cell death, alterations in gene expression, or increased cell survival as a result of alterations in neurotrophic factor production or availability.

Perturbation of target-directed neurite outgrowth in embryonic CNS co-cultures grown in the presence of ethanol

Studies were conducted to determine the influence of ethanol on target-directed fiber outgrowth in culture, using embryonic chick spinal cord-muscle, and fetal rat septal-hippocampal co-cultured explants. Process extension from the spinal cord and septal explants in control cultures was selectively oriented toward the appropriate target tissue. Ethanol in the culture medium (500 mg/dl) eliminated this target-oriented outgrowth in both systems, although the overall extent of neurite outgrowth was not affected. In an effort to further characterize the source of this disruption, target explants were grown alone, with and without ethanol, and the target-conditioned culture media was subsequently harvested and placed on newly plated spinal cord or septal explants, to determine whether ethanol decreased the target production of soluble substances. To determine whether deposition of substrate-bound materials by the target tissue was affected by ethanol, spinal cord or septal explants were plated in wells which had previously been occupied by the appropriate target tissue. These studies revealed that ethanol significantly inhibited production of soluble and substrate-bound materials by muscle explants, but not by hippocampal explants. It was concluded that the ethanol-induced loss of target-directed neurite outgrowth in the spinal cord explants could be accounted for primarily by the attenuated production of neurotropic/neurotropic substances by the muscle tissue. The loss of target-directionality in the septal explants appeared to be due to other factors, possibly related to ethanol-induced compromise of the capacity of the septal neurons to respond appropriately to target-derived neurotrophic/neurotropic substances. The implications of these results for the fetal alcohol syndrome are considered.

Effects of prenatal alcohol exposure on the postnatal morphology of the rat oculomotor nucleus

Morphological development of the rat oculomotor nucleus was investigated on postnatal day 15 following a prenatal ethanol exposure. Analysis of toluidine blue stained plastic sections showed that the prenatal alcohol exposure caused a decrease in the density of neurons and an increase in the density of astrocytes in the center of the nucleus. There was an alcohol-induced reduction in the overall size of the cross-sectional region of the oculomotor nucleus, but no effect on the number of neurons per unit area of that total oculomotor region, indicating a delay or alteration of the migration of neurons to their normal clustered position in the center of the nucleus. The areas of the neuronal cell nucleus and nucleolus were not affected by the alcohol exposure. Analysis of Golgi-Cox-impregnated multipolar neurons showed that the alcohol exposure caused a reduction in area of the cell soma; a reduction in the number of dendritic branches; and a reduction in the complexity of the dendritic arbor relative to distance from the soma, based on concentric ring analysis. The results of this study demonstrate that gestational alcohol exposure can retard the maturation of the oculomotor nucleus.

Ethanol influences on the chick embryo spinal cord motor system: analyses of motoneuron cell death, motility, and target trophic factor activity and in vitro analyses of neurotoxicity and trophic factor neuroprotection

A series of in vivo and in vitro experiments were conducted to determine the influence of prenatally administered ethanol on several aspects of the developing chick embryo spinal cord motor system. Specifically, we examined: (1) the effect of chronic ethanol administration during the natural cell death period on spinal cord motoneuron numbers; (2) the influence of ethanol on ongoing embryonic motility; (3) the effect of ethanol exposure on neurotrophic activity in motoneuron target tissue (limb bud); and (4) the responsiveness of cultured spinal cord neurons to ethanol, and the potential of target-derived neurotrophic factors to ameliorate ethanol neurotoxicity. These studies revealed the following: Chronic prenatal ethanol exposure reduces the number of motoneurons present in the lateral motor column after the cell death period [embryonic day 12 (E12)]. Ethanol tends to inhibit embryonic motility, particularly during the later stages viewed (E9-E11). Chronic ethanol exposure reduces the neurotrophic activity contained in target muscle tissue. Such diminished support could contribute to the observed motoneuron loss. Direct exposure of spinal cord neurons to ethanol decreases neuronal survival and process outgrowth in a dose-dependent manner, but the addition of target muscle extract to ethanol-containing cultures can ameliorate this ethanol neurotoxicity. These studies demonstrate ethanol toxicity in a population not previously viewed in this regard and suggest a mechanism that may be related to this cell loss (i.e., decreased neurotrophic support).

Combined pre- and postnatal ethanol exposure alters the development of Bergmann glia in rat cerebellum

The development and maturation of Bergmann glial cells in the rat cerebellum was evaluated on postnatal day 15 by glial fibrillary acidic protein (GFAP) immunocytochemistry, following combined gestational and 10-day postnatal ethanol exposure (a full three trimester human equivalency). GFAP-positive Bergmann glial fibers of lobules I, III, VIb, VII and X of the cerebellar vermis were examined and counted in the molecular layer (ML), the external granular layer (EGL) and the external limiting membrane (ELM). Ethanol exposure reduced: (1) the number of GFAP-positive fibers (per unit length of folia surface) at all three levels; (2) the percentage of mature fibers; and (3) the cross-sectional area in all lobules examined. When data from the five lobules were pooled, there were 7% fewer GFAP-positive fibers in the ML, 15% fewer in the EGL and 20% fewer in the ELM; the percentage of mature fibers was reduced by 16%; and the cross-sectional areas of lobules were reduced by 16%. The altered development of Bergmann glia could be one of the factors causing delayed migration of granular neurons and reductions in the number of granule cells reported in other studies following developmental ethanol exposures and could help to explain some of the motor dysfunctions reported in FAS victims.