Prenatal ethanol exposure, generalized learning impairment, and medial prefrontal cortical deficits in rats

How prenatal exposures shape the infant brain: Insights from infant neuroimaging studies

Brain development during the prenatal period is rapid and unparalleled by any other time during development. Biological systems undergoing rapid development are at higher risk for disorganizing influences. Therefore, certain prenatal exposures impact brain development, increasing risk for negative neurodevelopmental outcome. While prenatal exposures have been associated with cognitive and behavioral outcomes later in life, the underlying macroscopic brain pathways remain unclear. Here, we review magnetic resonance imaging (MRI) studies investigating the association between prenatal exposures and infant brain development focusing on prenatal exposures via maternal physical health factors, maternal mental health factors, and maternal drug and medication use. Further, we discuss the need for studies to consider multiple prenatal exposures in parallel and suggest future directions for this body of research.

Corticostriatal Circuit Models of Cognitive Impairments Induced by Fetal Exposure to Alcohol

The term fetal alcohol spectrum disorder includes a group of diseases caused by fetal alcohol exposure (FAE). Patients with fetal alcohol spectrum disorder display heterogeneous socioemotional and cognitive deficits, particularly in the domain of executive function, that share symptoms with other neuropsychiatric disorders. Despite the availability of several preclinical models, the developmental brain defects causally linked to behavioral deficits induced by FAE remain poorly understood. Here, we first review the effects of FAE on corticostriatal development and its impact on both corticostriatal pathway function and cognitive abilities. We propose three non-mutually exclusive circuit models of corticostriatal dysfunctions to account for some of the FAE-induced cognitive deficits. One model posits that associative-sensorimotor imbalance causes hyper goal-directed behavior, and a second model implies that alteration of prefrontal-striatal behavioral suppression circuits results in loss of behavioral inhibition. A third model suggests that local striatal circuit deficits affect striatal neuronal ensemble function to impair action selection and performance. Finally, we discuss how preclinical approaches applied to these circuit models could offer potential rescue strategies for executive function deficits in patients with fetal alcohol spectrum disorder.

Midline Thalamic Damage Associated with Alcohol-Use Disorders: Disruption of Distinct Thalamocortical Pathways and Function

The thalamus, a significant part of the diencephalon, is a symmetrical and bilateral central brain structure. The thalamus is subdivided into three major groups of nuclei based on their function: sensorimotor nuclei (or principal/relay nuclei), limbic nuclei and nuclei bridging these two domains. Anatomically, nuclei within the thalamus are described by their location, such as anterior, medial, lateral, ventral, and posterior. In this review, we summarize the role of medial and midline thalamus in cognition, ranging from learning and memory to flexible adaptation. We focus on the discoveries in animal models of alcohol-related brain damage, which identify the loss of neurons in the medial and midline thalamus as drivers of cognitive dysfunction associated with alcohol use disorders. Models of developmental ethanol exposure and models of adult alcohol-related brain damage and are compared and contrasted, and it was revealed that there are similar (anterior thalamus) and different (intralaminar [adult exposure] versus ventral midline [developmental exposure]) thalamic pathology, as well as disruptions of thalamo-hippocampal and thalamo-cortical circuits. The final part of the review summarizes approaches to recover alcohol-related brain damage and cognitive and behavioral outcomes. These approaches include pharmacological, nutritional and behavioral interventions that demonstrated the potential to mitigate alcohol-related damage. In summary, the medial/midline thalamus is a significant contributor to cognition function, which is also sensitive to alcohol-related brain damage across the life span, and plays a role in alcohol-related cognitive dysfunction.

Chronic alcohol exposure during critical developmental periods differentially impacts persistence of deficits in cognitive flexibility and related circuitry

Cognitive flexibility in decision making depends on prefrontal cortical function and is used by individuals to adapt to environmental changes in circumstances. Cognitive flexibility can be measured in the laboratory using a variety of discrete, translational tasks, including those that involve reversal learning and/or set-shifting ability. Distinct components of flexible behavior rely upon overlapping brain circuits, including different prefrontal substructures that have separable impacts on decision making. Cognitive flexibility is impaired after chronic alcohol exposure, particularly during development when the brain undergoes rapid maturation. This review examines how cognitive flexibility, as indexed by reversal and set-shifting tasks, is impacted by chronic alcohol exposure in adulthood, adolescent, and prenatal periods in humans and animal models. We also discuss areas for future study, including mechanisms that may contribute to the persistence of cognitive deficits after developmental alcohol exposure and the compacting consequences from exposure across multiple critical periods.

CE-123, a novel dopamine transporter inhibitor, attenuates locomotor hyperactivity and improves cognitive functions in rat model of fetal alcohol spectrum disorders

Perinatal alcohol exposure can lead to fetal alcohol spectrum disorders (FASD), usually first diagnosed in childhood, that are characterized by hyperactivity, impulsivity and learning and memory disability, among others. To test the hypothesis that dopamine signaling is one of the main factors underlying these impairments, a new atypical dopamine transporter (DAT) inhibitor, CE-123 (1, 3 or 10 mg/kg) was assessed for its potential to overcome the ethanol-induced behavioral effects in a rat model of FASD. In the present study, neonatal rats were exposed to alcohol intubations across the neonatal period (postnatal day (PND)4-9, the third trimester equivalent of human gestation) and, after weaning, the animals (male rats) were assigned randomly to three groups. The first group was tested at PND21 (hyperactivity test). A second group was tested at PND45 (anxiety test), at PND47 (locomotor activity test), at PND49 (spatial cognitive test in the Barnes maze) and PND50 (reversal learning in the Barnes maze). The third group was tested at PND50 (dopamine receptor mRNA expression). Our results support the hypothesis that dopamine signaling is associated with FASD because the dopamine (D1, D2 and D5) receptor mRNA expression was altered in the striatum, hippocampus and prefrontal cortex in adult rats exposed to ethanol during neonatal period. CE-123 (3 and 10 mg/kg) inhibited the hyperactivity and ameliorated (10 mg/kg) the impairment of reversal learning in alcohol-exposed rats. Thus, these findings provide support that CE-123 may be a useful intervention for same of the deficits associated with neonatal ethanol exposure.

Nucleus reuniens of the midline thalamus of a rat is specifically damaged after early postnatal alcohol exposure

Individuals diagnosed with fetal alcohol spectrum disorders often show behavioral impairments in executive functioning. Mechanistic studies have implicated coordination between the prefrontal cortex and the hippocampus (through thalamic nucleus reuniens) as essential for such executive functions. This study is the first to report the long-term neuroanatomical alterations to the ventral midline thalamus after alcohol exposure on postnatal days 4-9 (a rodent model of binge drinking during the third-trimester of human pregnancy). Alcohol added to a milk formula was administered to female Long-Evans rat pups on postnatal days 4-9 (5.25 g/kg/day of ethanol, intragastric intubation). Control animals were intubated without the administration of liquid. In adulthood, brains were immunohistochemically labeled for a neuronal marker (NeuN) conjugated with Cy3 fluorophore and stained with Hoechst33342 to visualize nuclei. Total non-neuronal cell number (NeuN/Hoechst) and neuron number (NeuN/Hoechst), and total volume were estimated using unbiased stereology in two neighboring midline thalamic nuclei: reuniens and rhomboid. Estimates were analyzed using linear mixed modeling to account for animal and litter as clustering variables. A 21% reduction in the total neuron number (resulting in altered neuron-to-non-neuron ratio) and an 18% reduction in total volume were found exclusively in thalamic nucleus reuniens in rats exposed to ethanol. Non-neuronal cell number was not changed in reuniens. No ethanol-induced changes on any measures were observed in rhomboid nucleus. These specific neuroanatomical alterations provide a necessary foundation for further examination of circuit-level alterations that occur in fetal alcohol spectrum disorder.

Moderate prenatal alcohol exposure impairs cognitive control, but not attention, on a rodent touchscreen continuous performance task

A common feature associated with fetal alcohol spectrum disorders is the inability to concentrate on a specific task while ignoring distractions. Human continuous performance tasks (CPT), measure vigilance and cognitive control simultaneously while these processes are traditionally measured separately in rodents. We recently established a touchscreen 5-choice CPT (5C-CPT) that measures vigilance and cognitive control simultaneously by incorporating both target and nontargets and showed it was sensitive to amphetamine-induced improvement in humans and mice. Here, we examined the effects of moderate prenatal alcohol exposure (PAE) in male and female mice on performance of the 5-choice serial reaction time task (5-CSRTT), which contained only target trials, and the 5C-CPT which incorporated both target and nontarget trials. In addition, we assessed gait and fine motor coordination in behavioral naïve PAE and control animals. We found that on the 5-CSRTT mice were able to respond to target presentations with similar hit rates regardless of sex or treatment. However, on the 5C-CPT PAE mice made significantly more false alarm responses vs controls. Compared with control animals, PAE mice had a significantly lower sensitivity index, a measure of ability to discriminate appropriate responses to stimuli types. During 5C-CPT, female mice, regardless of treatment, also had increased mean latency to respond when correct and omitted more target trials. Gait assessment showed no significant differences in PAE and SAC mice on any measure. These findings suggest that moderate exposure to alcohol during development can have long lasting effects on cognitive control unaffected by gross motor alterations.

An Emergent Discriminative Learning Is Elicited During Multifrequency Testing

In auditory-conditioned fear learning, the freezing response is independent of the sound frequencies used, but the frequency of the conditioned sound is considered distinct from those of unrelated sounds based on electrophysiological responses in the auditory system. Whether an emergent discriminative learning underlies auditory fear conditioning and which nuclei and pathways are involved in it remain unclear. Using behavioral and electrophysiological assays, we found that the response of medial prefrontal cortex (mPFC) neurons to a conditioned auditory stimulus (CS) was enhanced relative to the response to unrelated frequencies (UFs) after auditory fear conditioning, and mice could distinguish the CS during multifrequency testing, a phenomenon called emergent discriminative learning. After silencing the mPFC with muscimol, emergent discriminative learning was blocked. In addition, the pure tone responses of mPFC neurons were inhibited after injection of lidocaine in the ipsilateral primary auditory cortex (A1), and the emergent discriminative learning was blocked by silencing both sides of A1 with muscimol. This study, therefore, provides evidence for an emergent discriminative learning mediated by mPFC and A1 neurons after auditory fear conditioning.

[Experimental approaches to the investigation of behavioral disorders associated with prenatal alcohol exposure]

Fetal alcohol spectrum disorders (FASD) is an umbrella term which covers a wide range of deficits in prenatal and postnatal growth, anatomy and CNS functions produced by prenatal alcohol exposure. The most severe form of FASD is fetal alcohol syndrome (FAS) characterized by additional specific craniofacial and brain malformations. Despite a high prevalence and extensive clinical studies, the fundamental mechanisms of FASD are still poorly understood. Thereby, experimental models, which allow better control for both socio-environmental and genetic factors, are critical to our understanding of FASD. The review is focused on the effects of exposure to alcohol during the prenatal period in animal models. The authors outline that prenatally alcohol-induced changes in motor and executive functions, learning and memory, stress reactivity and affective state are remarkably parallel between animals and humans. Finally, the authors consider a potential impact of postnatal social and environmental factors on the outcome in experimental models of FASD.

Functional Connectivity and Metabolic Alterations in Medial Prefrontal Cortex in a Rat Model of Fetal Alcohol Spectrum Disorder: A Resting-State Functional Magnetic Resonance Imaging and in vivo Proton Magnetic Resonance Spectroscopy Study

Prenatal ethanol exposure alters brain structure, functional connectivity, and behavior in humans and rats. Behavioral changes include deficits in executive function, which requires cooperative activity between the frontal cortices and other brain regions. In this study, we analyzed the functional connectivity and neurochemical levels of the prefrontal cortex (PFC) using resting-state functional magnetic resonance imaging (rsfMRI) and proton magnetic resonance spectroscopy (1H-MRS) in ethanol-exposed (Eth) and control (Ctr) rats. Pregnant Long-Evans rats were fed a liquid diet containing ethanol (2.1-6.46% v/v ethanol) from gestational days 6 to 21 (Eth). Ctr animals received an isocaloric, isonutritive liquid diet. In young adulthood, male and female offspring underwent in vivo MRI using a 7.0-Tesla system. 1H-MRS from the PFC and whole brain rsfMRI were obtained on the animals. Seed-based functional connectivity analysis was performed with seeds placed in the PFC, matching the voxel of MRS. Male, but not female, Eth rats showed less functional connectivity between PFC and dorsal striatum than Ctr animals. In Eth males glucose levels were significantly lower, and in Eth females lower levels of phosphorylcholine but an increased gamma-aminobutyric acid/glutamate ratio were observed in the PFC compared with Ctr animals. Prenatal ethanol alters brain metabolism and functional connectivity of the PFC in a sex-dependent manner.

Prenatal alcohol exposure disrupts male adolescent social behavior and oxytocin receptor binding in rodents

Social behavior deficits resulting from prenatal alcohol exposure (PAE) emerge early in life and become more pronounced across development. Maturational changes associated with adolescence, including pubertal onset, can have significant consequences for social behavior development, making adolescence a unique period of increased vulnerability to social behavior dysfunction. Unfortunately, little is known about the underlying neurobiology supporting PAE-related social behavior impairments, particularly in the context of adolescence, when the transition to a more complex social environment may exacerbate existing deficits in social behavior function. Here we perform a comprehensive evaluation of social behavior development in PAE animals during two different periods in adolescence using three separate but related tests of social behavior in increasingly complex social contexts: the social interaction test, the social recognition memory test (i.e. habituation-dishabituation test), and the social discrimination test. Additionally, we investigated the underlying neurobiology of the oxytocin (OT) and vasopressin (AVP) systems following PAE, given their well-documented role in mediating social behavior. Our results demonstrate that compared to controls, early adolescent PAE animals showed impairments on the social recognition memory test and increased OT receptor binding in limbic networks, while late adolescent PAE animals exhibited impairments on the social discrimination test and increased OTR binding in forebrain reward systems. Taken together, these data indicate that PAE impairs adolescent social behavior - especially with increasing complexity of the social context - and that impairments are associated with altered development of the OT but not the AVP system.

Meta-Analyses of Externalizing Disorders: Genetics or Prenatal Alcohol Exposure?

BACKGROUND

Externalizing disorders are heritable precursors to alcohol dependence, common in children of alcoholics (COA), and in children with prenatal alcohol exposure (PAE). Pregnancies involving alcohol exposure sufficient to affect the fetus may involve women with genetic risk for alcohol dependence. We hypothesized that known PAE will increase the odds of having an externalizing disorder compared to COA.

METHODS

The odds ratios of 3 externalizing disorders (attention-deficit hyperactivity disorder [ADHD], conduct disorder [CD], and oppositional defiant disorder [ODD]) were obtained for 2 domains: (i) PAE and (ii) COA, by estimating the logged odds ratio (LOR) for each study. Permutation tests were implemented to compare LORs for PAE versus COA studies within each disorder, including PAE versus an alcohol dependent (AD) mother and PAE versus an AD father.

RESULTS

In PAE studies, the odds of ADHD and CD were elevated. Rates of all 3 disorders were elevated in COA studies. Permutation tests revealed that the mean LOR for ADHD was significantly higher in PAE studies compared to: COA (p = 0.01), AD mother (p < 0.05), and AD father (p = 0.03). No differences were found for ODD (p = 0.09) or CD (p = 0.21).

CONCLUSIONS

These results provide compelling evidence of an increased risk of ADHD in those with PAE beyond that due to parental alcohol dependence or a genetic liability, consistent with a unique etiology most likely due to direct alcohol exposure during prenatal development.

Choline and Working Memory Training Improve Cognitive Deficits Caused by Prenatal Exposure to Ethanol

Prenatal ethanol exposure is associated with deficits in executive function such as working memory, reversal learning and attentional set shifting in humans and animals. These behaviors are dependent on normal structure and function in cholinergic brain regions. Supplementation with choline can improve many behaviors in rodent models of fetal alcohol spectrum disorders and also improves working memory function in normal rats. We tested the hypothesis that supplementation with choline in the postnatal period will improve working memory during adolescence in normal and ethanol-exposed animals, and that working memory engagement during adolescence will transfer to other cognitive domains and have lasting effects on executive function in adulthood. Male and female offspring of rats fed an ethanol-containing liquid diet (ET; 3% v/v) or control dams given a non-ethanol liquid diet (CT) were injected with choline (Cho; 100 mg/kg) or saline (Sal) once per day from postnatal day (P) 16–P30. Animals were trained/tested on a working memory test in adolescence and then underwent attentional set shifting and reversal learning in young adulthood. In adolescence, ET rats required more training to reach criterion than CT-Sal. Choline improved working memory performance for both CT and ET animals. In young adulthood, ET animals also performed poorly on the set shifting and reversal tasks. Deficits were more robust in ET male rats than female ET rats, but Cho improved performance in both sexes. ET male rats given a combination of Cho and working memory training in adolescence required significantly fewer trials to achieve criterion than any other ET group, suggesting that early interventions can cause a persistent improvement.

Preserved cortical asymmetry despite thinner cortex in children and adolescents with prenatal alcohol exposure and associated conditions

Prenatal alcohol exposure (PAE) is associated with reduced overall brain volume. Although this has been reported consistently across studies, the status of cortical thickness after PAE is more variable. The cortex is asymmetric in typical controls, but it is unclear whether the left and right counter parts of the cortical gray matter are unevenly influenced in postpartum brain development after PAE. Brain MRI was acquired in a newly recruited sample of 157 participants (PAE: N = 78, 5.5-18.9 years, 40 females and controls: N = 79, 5.8-18.5 years, 44 females) across four Canadian sites in the NeuroDevNet project. The PAE group had other confounds such as psychiatric co-morbidity, different living environment, and so on, not present in the control group. In agreement with previous studies, the volumes of all brain structures were reduced in PAE compared to controls, including gray and white matter of cerebrum and cerebellum, and all deep gray matter including the hippocampus, amygdala, thalamus, caudate, putamen, and pallidum. The PAE group showed reductions in global and regional cortical thickness, while the pattern and degree of cortical thickness asymmetry were preserved in PAE participants with the greatest rightward asymmetry in the lateral parietal lobe and the greatest leftward asymmetry in the lateral frontal cortex. This persistent asymmetry reflects that the homologous left and right cortical regions followed typical relative developmental patterns in the PAE group despite being thinner bilaterally than controls. Hum Brain Mapp 39:72-88, 2018. © 2017 Wiley Periodicals, Inc.

Behavioral deficits induced by third-trimester equivalent alcohol exposure in male C57BL/6J mice are not associated with reduced adult hippocampal neurogenesis but are still rescued with voluntary exercise

Prenatal alcohol exposure can produce permanent alterations in brain structure and profound behavioral deficits. Mouse models can help discover mechanisms and identify potentially useful interventions. This study examined long-term influences of either a single or repeated alcohol exposure during the third-trimester equivalent on survival of new neurons in the hippocampus, behavioral performance on the Passive avoidance and Rotarod tasks, and the potential role of exercise as a therapeutic intervention. C57BL/6J male mice received either saline or 5g/kg ethanol split into two s.c. injections, two hours apart, on postnatal day (PD)7 (Experiment 1) or on PD5, 7 and 9 (Experiment 2). All mice were weaned on PD21 and received either a running wheel or remained sedentary from PD35-PD80/81. From PD36-45, mice received i.p. injections of 50mg/kg bromodeoxyuridine (BrdU) to label dividing cells. Behavioral testing occurred between PD72-79. Number of surviving BrdU+ cells and immature neurons (doublecortin; DCX+) was measured at PD80-81. Alcohol did not affect number of BrdU+ or DCX+ cells in either experiment. Running significantly increased number of BrdU+ and DCX+ cells in both treatment groups. Alcohol-induced deficits on Rotarod performance and acquisition of the Passive avoidance task (Day 1) were evident only in Experiment 2 and running rescued these deficits. These data suggest neonatal alcohol exposure does not result in long-term impairments in adult hippocampal neurogenesis in the mouse model. Three doses of ethanol were necessary to induce behavioral deficits. Finally, the mechanisms by which exercise ameliorated the neonatal alcohol induced behavioral deficits remain unknown.

The impact of prenatal alcohol exposure on social, cognitive and affective behavioral domains: Insights from rodent models

Fetal Alcohol Spectrum Disorders (FASD) are characterized by deficits in working memory, response inhibition, and behavioral flexibility. However, the combination and severity of impairments are highly dependent upon maternal ethanol consumption patterns, which creates a complex variety of manifestations. Rodent models have been essential in identifying behavioral endpoints of prenatal alcohol exposure (PAE). However, experimental model outcomes are extremely diverse based on level, pattern, timing, and method of ethanol exposure, as well as the behavioral domain assayed and paradigm used. Therefore, comparisons across studies are difficult and there is currently no clear comprehensive behavioral phenotype of PAE. This lack of defined cognitive and behavioral phenotype is a contributing factor to the difficulty in identifying FASD individuals. The current review aims to critically examine preclinical behavioral outcomes in the social, cognitive, and affective domains in terms of the PAE paradigm, with a special emphasis on dose, timing, and delivery, to establish a working model of behavioral impairment. In addition, this review identifies gaps in our current knowledge and proposes future areas of research that will advance knowledge in the field of PAE outcomes. Understanding the complex behavioral phenotype, which results from diverse ethanol consumption will allow for development of better diagnostic tools and more critical evaluation of potential treatments for FASD.

Alcohol exposure in utero perturbs retinoid homeostasis in adult rats

BACKGROUND

Maternal alcohol exposure and adult alcohol intake have been shown to perturb the metabolism of various micro- and macro-nutrients, including vitamin A and its derivatives (retinoids). Therefore, it has been hypothesized that the well-known detrimental consequences of alcohol consumption may be due to deregulations of the metabolism of such nutrients rather than to a direct effect of alcohol. Alcohol exposure in utero also has long-term harmful consequences on the health of the offspring with mechanisms that have not been fully clarified. Disruption of tissue retinoid homeostasis has been linked not only to abnormal embryonic development, but also to various adult pathological conditions, including cancer, metabolic disorders and abnormal lung function. We hypothesized that prenatal alcohol exposure may permanently perturb tissue retinoid metabolism, predisposing the offspring to adult chronic diseases.

METHODS

Serum and tissues (liver, lung and prostate from males; liver and lung from females) were collected from 60-75 day-old sprague dawley rats born from dams that were: (I) fed a liquid diet containing 6.7% alcohol between gestational day 7 and 21; or (II) pair-fed with isocaloric liquid diet during the same gestational window; or (III) fed ad libitum with regular rat chow diet throughout pregnancy. Serum and tissue retinoid levels were analyzed by reverse-phase high-performance liquid chromatography (HPLC). Serum retinol-binding protein (RBP) levels were measured by western blot analysis, and liver, lung and prostate mRNA levels of lecithin-retinol acyltransferase (LRAT) were measured by qPCR.

RESULTS

Retinyl ester levels were significantly reduced in the lung of both males and females, as well as in the liver and ventral prostate of males born from alcohol-fed dams. Tissue LRAT mRNA levels remained unchanged upon maternal alcohol treatment.

CONCLUSIONS

Prenatal alcohol exposure in rats affects retinoid metabolism in adult life, in a tissue- and sex-dependent manner. We propose that the alcohol-induced perturbations of vitamin A metabolism may predispose to detrimental consequnces on adult health.

Moderate prenatal alcohol exposure enhances GluN2B containing NMDA receptor binding and ifenprodil sensitivity in rat agranular insular cortex

Prenatal exposure to alcohol affects the expression and function of glutamatergic neurotransmitter receptors in diverse brain regions. The present study was undertaken to fill a current gap in knowledge regarding the regional specificity of ethanol-related alterations in glutamatergic receptors in the frontal cortex. We quantified subregional expression and function of glutamatergic neurotransmitter receptors (AMPARs, NMDARs, GluN2B-containing NMDARs, mGluR1s, and mGluR5s) by radioligand binding in the agranular insular cortex (AID), lateral orbital area (LO), prelimbic cortex (PrL) and primary motor cortex (M1) of adult rats exposed to moderate levels of ethanol during prenatal development. Increased expression of GluN2B-containing NMDARs was observed in AID of ethanol-exposed rats compared to modest reductions in other regions. We subsequently performed slice electrophysiology measurements in a whole-cell patch-clamp preparation to quantify the sensitivity of evoked NMDAR-mediated excitatory postsynaptic currents (EPSCs) in layer II/III pyramidal neurons of AID to the GluN2B negative allosteric modulator ifenprodil. Consistent with increased GluN2B expression, ifenprodil caused a greater reduction in NMDAR-mediated EPSCs from prenatal alcohol-exposed rats than saccharin-exposed control animals. No alterations in AMPAR-mediated EPSCs or the ratio of AMPARs/NMDARs were observed. Together, these data indicate that moderate prenatal alcohol exposure has a significant and lasting impact on GluN2B-containing receptors in AID, which could help to explain ethanol-related alterations in learning and behaviors that depend on this region.

An fMRI study of behavioral response inhibition in adolescents with and without histories of heavy prenatal alcohol exposure

Heavy prenatal alcohol exposure results in a range of deficits, including both volumetric and functional changes in brain regions involved in response inhibition such as the prefrontal cortex and striatum. The current study examined blood oxygen level-dependent (BOLD) response during a stop signal task in adolescents (ages 13-16 y) with histories of heavy prenatal alcohol exposure (AE, n=21) and controls (CON, n=21). Task performance was measured using percent correct inhibits during three difficulty conditions: easy, medium, and hard. Group differences in BOLD response relative to baseline motor responding were examined across all inhibition trials and for each difficulty condition separately. The contrast between hard and easy trials was analyzed to determine whether increasing task difficulty affected BOLD response. Groups had similar task performance and demographic characteristics, except for full scale IQ scores (AE<CON). The AE group demonstrated greater BOLD response in frontal, sensorimotor, striatal, and cingulate regions relative to controls, especially as task difficulty increased. When contrasting hard vs. easy inhibition trials, the AE group showed greater medial/superior frontal and cuneus BOLD response than controls. Results were unchanged after demographics and FAS diagnosis were statistically controlled. This was the first fMRI study to utilize a stop signal task, isolating fronto-striatal functioning, to assess response inhibition and the effects task difficulty in adolescents with prenatal alcohol exposure. Results suggest that heavy prenatal alcohol exposure disrupts neural function of this circuitry, resulting in immature cognitive processing and motor-association learning and neural compensation during response inhibition.

Sex differences in cognitive impairment and Alzheimer's disease

Studies have shown differences in specific cognitive ability domains and risk of Alzheimer's disease between the men and women at later age. However it is important to know that sex differences in cognitive function during adulthood may have their basis in both organizational effects, i.e., occurring as early as during the neuronal development period, as well as in activational effects, where the influence of the sex steroids influence brain function in adulthood. Further, the rate of cognitive decline with aging is also different between the sexes. Understanding the biology of sex differences in cognitive function will not only provide insight into Alzheimer's disease prevention, but also is integral to the development of personalized, gender-specific medicine. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of sex differences in cognitive function from young to old, and examines the effects of sex hormone treatments on Alzheimer's disease in men and women.

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

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

Examination of age-dependent effects of fetal ethanol exposure on behavior, hippocampal cell counts, and doublecortin immunoreactivity in rats

Ethanol is known as a potent teratogen having adverse effects on brain and behavior. However, some of the behavioral deficits caused by fetal alcohol exposure and well expressed in juveniles ameliorate with maturation may suggest some kind of functional recovery occurring during postnatal development. The aim of this study was to reexamine age-dependent behavioral impairments in fetal-alcohol rats and to investigate the changes in neurogenesis and gross morphology of the hippocampus during a protracted postnatal period searching for developmental deficits and/or delays that would correlate with behavioral impairments in juveniles and for potential compensatory processes responsible for their amelioration in adults. Ethanol was delivered to the pregnant dams by intragastric intubation throughout 7-21 gestation days at daily dose of 6 g/kg. Isocaloric intubation and intact control groups were included. Locomotor activity, anxiety, and spatial learning tasks were applied to juvenile and young-adult rats from all groups. Unbiased stereological estimates of hippocampal volumes, the total number of pyramidal and granular cells, and double cortin expressing neurons were carried out for postnatal days (PDs) PD1, PD10, PD30, and PD60. Alcohol insult during second trimester equivalent caused significant deficits in the spatial learning in juvenile rats; however, its effect on hippocampal morphology was limited to a marginally lower number of granular cells in dentate gyrus (DG) on PD30. Thus, initial behavioral deficits and the following functional recovery in fetal-alcohol subjects may be due to more subtle plastic changes within the hippocampal formation but also in other structures of the extended hippocampal circuit. Further investigation is required.

Cyr S, Jablonski S, Hunt P, Klintsova A, Stanton M. Effects of exercise and environmental complexity on deficits in trace and contextual fear conditioning produced by neonatal alcohol exposure in rats

In rodents, voluntary exercise and environmental complexity increases hippocampal neurogenesis and reverses spatial learning and long-term potentiation deficits in animals prenatally exposed to alcohol. The present experiment extended these findings to neonatal alcohol exposure and to delay, trace, and contextual fear conditioning. Rats were administered either 5.25 g/kg/day alcohol via gastric intubation or received sham-intubations (SI) between Postnatal Day (PD) 4 and 9 followed by either free access to a running wheel on PD 30-41 and housing in a complex environment on PD 42-72 (wheel-running plus environmental complexity; WREC) or conventional social housing (SHSH) from PD 30 to 72. Adult rats (PD 80 ± 5) received 5 trials/day of a 10-s flashing-light conditioned stimulus (CS) paired with .8 mA footshock either immediately (delay conditioning) or after a 10-s trace interval (trace conditioning) for 2 days. Neonatal alcohol exposure impaired context and trace conditioning, but not short-delay conditioning. The WREC intervention did not reverse these deficits, despite increasing context-related freezing in ethanol-exposed and SI animals.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

The effect of low-to-moderate-dose ethanol consumption on rat mammary gland structure and function and early postnatal growth of offspring

High levels of alcohol consumption during pregnancy can lead to growth deficits in early postnatal life. However, the effects of low-to-moderate alcohol consumption during pregnancy are less clearly defined. The aim of this study was to determine whether low-to-moderate ethanol (EtOH) consumption throughout pregnancy in the rat alters maternal mammary gland morphology and milk protein levels, thereby affecting lactation and the growth of pups after birth. Sprague-Dawley rats were fed an ad libitum liquid diet ± 6% vol/vol EtOH throughout pregnancy. Mammary glands from dams were collected at embryonic day (E) 20 or postnatal day (PN) 1, and expression of milk proteins (α-lactalbumin, β-casein, and whey acidic protein) was examined. In addition, relative amounts of alveoli, lactiferous ducts, adipose tissue, and blood vessels were determined at PN1. A subset of rats gave birth, and offspring growth and milk intake were recorded. Mammary gland weight was unaltered by EtOH, and stereological analysis showed no differences in gland structure compared with control. Although there were no significant changes in mammary gland gene expression at the RNA level, protein levels of α-lactalbumin were increased and whey acidic protein were decreased by EtOH. Offspring of EtOH-fed dams consumed less milk than controls in the lactational period; however, this did not alter their early postnatal growth. Overall, it appears that low-to-moderate-dose prenatal EtOH exposure does not significantly alter mammary gland development but may alter the composition of the various proteins found within the milk in a manner that maintains overall pup growth.

Hippocampal-dependent Pavlovian conditioning in adult rats exposed to binge-like doses of ethanol as neonates

Binge-like postnatal ethanol exposure produces significant damage throughout the brain in rats, including the cerebellum and hippocampus. In the current study, cue- and context-mediated Pavlovian conditioning were assessed in adult rats exposed to moderately low (3E; 3g/kg/day) or high (5E; 5g/kg/day) doses of ethanol across postnatal days 4-9. Ethanol-exposed and control groups were presented with 8 sessions of trace eyeblink conditioning followed by another 8 sessions of delay eyeblink conditioning, with an altered context presented over the last two sessions. Both forms of conditioning rely on the brainstem and cerebellum, while the more difficult trace conditioning also requires the hippocampus. The hippocampus is also needed to gate or modulate expression of the eyeblink conditioned response (CR) based on contextual cues. Results indicate that the ethanol-exposed rats were not significantly impaired in trace EBC relative to control subjects. In terms of CR topography, peak amplitude was significantly reduced by both doses of alcohol, whereas onset latency but not peak latency was significantly lengthened in the 5E rats across the latter half of delay EBC in the original training context. Neither dosage resulted in significant impairment in the contextual gating of the behavioral response, as revealed by similar decreases in CR production across all four treatment groups following introduction of the novel context. Results suggest ethanol-induced brainstem-cerebellar damage can account for the present results, independent of the putative disruption in hippocampal development and function proposed to occur following postnatal ethanol exposure.

An NCAM mimetic, FGL, alters hippocampal cellular morphometry in young adult (4 month-old) rats

The neural cell adhesion molecule, NCAM, is ubiquitously expressed within the CNS and has roles in development, cognition, neural plasticity and regulation of the immune system. NCAM is thus potentially an important pharmacological target for treatment of brain diseases. A cell adhesion mimetic FGL, a 15 amino-acid peptide derived from the second fibronectin type-III module of NCAM, has been shown to act as a neuroprotective agent in experimental disease and ageing models, restoring hippocampal/cognitive function and markedly alleviating deleterious changes in the CNS. However, the effects of FGL on the hippocampus of young healthy rats are unknown. The present study has examined the cellular neurobiological consequences of subcutaneous injections of FGL, on hippocampal cell morphometry in young (4 month-old) rats. We determined the effects of FGL on hippocampal volume, pyramidal neuron number/density (using unbiased quantitative stereology), and examined aspects of neurogenesis (using 2D morphometric analyses). FGL treatment reduced total volume of the dorsal hippocampus (associated with a decrease in total pyramidal neuron numbers in CA1 and CA3), and elevated the number of doublecortin immunolabeled neurons in the dentate gyrus, indicating a likely influence on neurogenesis in young healthy rats. These data indicate that FGL has a specific age dependent effect on the hippocampus, differing according to the development and maturity of the CNS.

Effects of ethanol during adolescence on the number of neurons and glia in the medial prefrontal cortex and basolateral amygdala of adult male and female rats

Human adolescents often consume alcohol in a binge-like manner at a time when changes are occurring within specific brain structures, such as the medial prefrontal cortex (mPFC) and the basolateral nucleus of the amygdala (BLN). In particular, the number of neurons and glia is changing in both of these areas in the rat between adolescence and adulthood (Markham et al., 2007; Rubinow and Juraska, 2009). The current study investigated the effects of ethanol exposure during adolescence on the number of neurons and glia in the adult mPFC and BLN in Long-Evans male and female rats. Saline or 3g/kg ethanol was administered between postnatal days (P) 35-45 in a binge-like pattern, with 2days of injections followed by 1 day without an injection. Stereological analyses of the ventral mPFC (prelimbic and infralimbic areas) and the BLN were performed on brains from rats at 100 days of age. Neuron and glia densities were assessed with the optical disector and then multiplied by the volume to calculate the total number of neurons and glia. In the adult mPFC, ethanol administration during adolescence resulted in a decreased number of glia in males, but not females, and had no effect on the number of neurons. Adolescent ethanol exposure had no effects on glia or neuron number in the BLN. These results suggest that glia cells in the prefrontal cortex are particularly sensitive to binge-like exposure to ethanol during adolescence in male rats only, potentially due to a decrease in proliferation in males or protective mechanisms in females.

Altered spatial learning and delay discounting in a rat model of human third trimester binge ethanol exposure

Ethanol exposure during perinatal development can cause cognitive abnormalities including difficulties in learning, attention, and memory, as well as heightened impulsivity. The purpose of this study was to assess performance in spatial learning and impulsive choice tasks in rats subjected to an intragastric intubation model of binge ethanol exposure during human third trimester-equivalent brain development. Male and female Sprague-Dawley rat pups were intubated with ethanol (5.25 g/kg/day) on postnatal days 4-9. At adolescence (between postnatal days 35-38), these rats and sham intubated within-litter controls were trained in both spatial and cued versions of the Morris water maze. A subset of the male rats was subsequently tested on a delay-discounting task to assess impulsive choice. Ethanol-exposed rats were spatially impaired relative to controls, but performed comparably to controls on the cued version of the water maze. Ethanol-exposed rats also showed greater preference for large delayed rewards on the delay discounting task, but no evidence for altered reward sensitivity or perseverative behavior. These data demonstrate that early postnatal intermittent binge-like ethanol exposure has prolonged, detrimental, but selective effects on cognition, suggesting that even relatively brief ethanol exposure late in human pregnancy can be deleterious for cognitive function.

Acute and long-term Purkinje cell loss following a single ethanol binge during the early third trimester equivalent in the rat

BACKGROUND

In the rat, binge-like ethanol (EtOH) exposure during the early neonatal period (a developmental period equivalent to the human third trimester) can result in a permanent deficit of cerebellar Purkinje cells (Pcells). However, the consequences of a moderate binge alcohol exposure on a single day during this postnatal period have not been established. This is an issue of importance as many pregnant women binge drink periodically at social drinking levels. This study aimed to identify both the acute and long-term effects of exposure to a single alcohol binge that achieved a mean peak blood EtOH concentration of approximately 250 mg/dl during early postnatal life using a rat model of fetal alcohol spectrum disorders.

METHODS

Acute apoptotic Pcell death 10 hours after a moderate dose binge EtOH exposure from postnatal days (PDs) 0 to 10 was assessed using active caspase-3 immunolabeling. Acute Pcell apoptosis was quantified in cerebellar vermal lobules I-X using the physical disector method. Long-term effects were assessed at PD 60 using stereological methods to determine total Pcell numbers in the vermis, lobule III, and lobule IX, following a moderate dose binge EtOH exposure at PDs 0, 2, or 4.

RESULTS

Acute apoptosis was induced by EtOH on PDs 1 to 8 in a time and lobular-dependent manner. For EtOH exposure on PD 2, significant long-term Pcell loss occurred in lobule III. EtOH exposure on PD 4 resulted in significant long-term Pcell loss throughout the entire vermis.

CONCLUSIONS

These results indicate that a single, early EtOH episode of moderate dose can create significant and permanent Pcell loss in the developing cerebellum.

Alcohol exposure in utero leads to enhanced prepubertal mammary development and alterations in mammary IGF and estradiol systems

Exposure to alcohol during fetal development increases susceptibility to mammary cancer in adult rats. This study determined if early changes in mammary morphology and the insulin-like growth factor (IGF)/estradiol axis are involved in the mechanisms that underlie this increased susceptibility. Pregnant Sprague-Dawley rats were fed a liquid diet containing 6.7% ethanol (alcohol), an isocaloric liquid diet (pair-fed), or rat chow ad libitum from days 11 to 21 of gestation. At birth, female pups were cross-fostered to ad libitum-fed control dams. Offspring were euthanized at postnatal days (PND) 20, 40, or 80. Animals were injected with BrdU before euthanasia, then mammary glands, serum, and livers were collected. Mammary glands from animals exposed to alcohol in utero displayed increased epithelial cell proliferation and aromatase expression at PND 20 and 40. Mammary IGF-I mRNA was higher in alcohol-exposed animals relative to controls at PND 20, while mammary IGFBP-5 mRNA was lower in this group at PND 40. Hepatic IGF-I mRNA expression was increased at all time points in alcohol-exposed animals, however, circulating IGF-I levels were not altered. These data indicate that alcohol exposure in utero may advance mammary development via the IGF and estradiol systems, which could contribute to increased susceptibility to mammary cancer later in life.

Executive function and memory in children with Fetal Alcohol Spectrum Disorder

A complex relation exists between memory and executive functioning (EF), particularly when learning and recalling multifaceted or extensive information ( Moscovitch & Winocur, 2002 ). A common instrument for evaluating this relationship is the Rey-Osterrieth Complex Figure (ROCF; Rey, 1941 ; Osterrieth, 1944 ). The ROCF has proved particularly useful in pediatric research; however, little research has been conducted among children with Fetal Alcohol Spectrum Disorders (FASD). Seventy children (35 FASD, 35 control), aged 6 to 12 years, were tested using the ROCF. All participants with FASD had received a diagnosis according to the Canadian guidelines for FASD ( Chudley et al., 2005 ) using the 4-digit diagnostic code ( Astley, 2004 ). Significant group differences were revealed with children with FASD demonstrating substantial difficulties in organization, accuracy, and memory. Among children with FASD, a distinctive profile emerged, lending support to the argument that children with FASD experience deficits in EF and memory throughout their development. Information from the present study will not only help to improve understanding of functioning in this population but also provide insight into how to deal with EF and memory deficits in terms of testing, treatment, and intervention.

Selective effects of perinatal ethanol exposure in medial prefrontal cortex and nucleus accumbens

Ethanol exposure during development is the leading known cause of mental retardation and can result in characteristic physiological and cognitive deficits, often termed Fetal Alcohol Spectrum Disorders (FASD). Previous behavioral findings using rat models of FASD have suggested that there are changes in the nucleus accumbens (NAC) and medial prefrontal cortex (mPFC) following ethanol exposure during development. This study used a rat model of FASD to evaluate dendritic morphology in both the NAC and mPFC and cell number in the NAC. Dendritic morphology in mPFC and NAC was assessed using a modified Golgi stain and analyzed via three dimensional reconstructions with Neurolucida (MBF Bioscience). Cell counts in the NAC (shell and core) were determined using an unbiased stereology procedure (Stereo Investigator (MBF Bioscience)). Perinatal ethanol exposure did not affect neuronal or glial cell population numbers in the NAC. Ethanol exposure produced a sexually dimorphic effect on dendritic branching at one point along the NAC dendrites but was without effect on all other measures of dendritic morphology in the NAC. In contrast, spine density was reduced and distribution was significantly altered in layer II/III neurons of the mPFC following ethanol exposure. Ethanol exposure during development was also associated with an increase in soma size in the mPFC. These findings suggest that previously observed sexually dimorphic changes in activation of the NAC in a rat model of FASD may be due to altered input from the mPFC.

Developmental cortical thinning in fetal alcohol spectrum disorders

Regional cortical thickness was evaluated using CIVET processing of 3D T1-weighted images (i) to compare the variation in cortical thickness between 33 participants with fetal alcohol spectrum disorders (FASD) aged 6-30 years (mean age 12.3 years) versus 33 age/sex/hand-matched controls, and (ii) to examine developmental changes in cortical thickness with age from children to young adults in both groups. Significant cortical thinning was found in the participants with FASD in large areas of the bilateral middle frontal lobe, pre- and post- central areas, lateral and inferior temporal and occipital lobes compared to controls. No significant cortical thickness increases were observed for the FASD group. Cortical thinning with age in a linear model was observed in both groups, but the locations were different for each group. FASD participants showed thinning with age in the left middle frontal, bilateral precentral, bilateral precuneus and paracingulate, left inferior occipital and bilateral fusiform gyri; while controls showed decreases with age in the bilateral middle frontal gyrus, right inferior frontal gyrus, bilateral precuneus gyrus, and bilateral occipital gyrus. A battery of cognitive assessments of memory, attention, motor, and verbal abilities was conducted with many of the FASD participants, but no significant correlations were found between these cognitive scores and regional cortical thickness. Non-invasive measurements of cortical thickness in children to young adults with FASD have identified both key regions of cortex that may be more deleteriously affected by prenatal alcohol exposure as well as cortical changes with age that differ from normal developmental thinning.

The effects of prenatal alcohol exposure on behavior: rodent and primate studies

The use of alcohol by women during pregnancy is a continuing problem. In this review the behavioral effects of prenatal alcohol from animal models are described and related to studies of children and adults with FASD. Studies with monkeys and rodents show that prenatal alcohol exposure adversely affects neonatal orienting, attention and motor maturity, as well as activity level, executive function, response inhibition, and sensory processing later in life. The primate moderate dose behavioral findings fill an important gap between human correlational data and rodent mechanistic research. These animal findings are directly translatable to human findings. Moreover, primate studies that manipulated prenatal alcohol exposure and prenatal stress independently show that prenatal stress exacerbates prenatal alcohol-induced behavioral impairments, underscoring the need to consider stress-induced effects in fetal alcohol research. Studies in rodents and primates show long-term effects of prenatal and developmental alcohol exposure on dopamine system functioning, which could underpin the behavioral effects.

Fetal alcohol exposure increases mammary tumor susceptibility and alters tumor phenotype in rats

BACKGROUND

Altered fetal programming because of a suboptimal in utero environment has been shown to increase susceptibility to many diseases later in life. This study examined the effect of alcohol exposure in utero on N-nitroso-N-methylurea (NMU)-induced mammary cancer risk during adulthood.

METHODS

Study 1: Pregnant Sprague Dawley rats were fed a liquid diet containing 6.7% ethanol (alcohol-fed), an isocaloric liquid diet (pair-fed), or rat chow ad libitum (ad lib-fed) from day 11 to 21 of gestation. At birth, female pups were cross-fostered to ad lib-fed control dams. Adult offspring were given an I.P. injection of NMU at a dose of 50 mg/kg body weight. Mammary glands were palpated for tumors twice a week, and rats were euthanized at 23 weeks postinjection. Study 2: To investigate the role of estradiol (E2), animals were exposed to the same in utero treatments but were not given NMU. Serum was collected during the preovulatory phase of the estrous cycle.

RESULTS

At 16 weeks postinjection, overall tumor multiplicity was greater in the offspring from the alcohol-fed group compared to the control groups, indicating a decrease in tumor latency. At study termination, 70% of all animals possessed tumors. Alcohol-exposed animals developed more malignant tumors and more estrogen receptor-α-negative tumors relative to the control groups. In addition, IGF-binding protein-5 (IGFBP-5) mRNA and protein were decreased in tumors of alcohol-exposed animals. Study 2 showed that alcohol-fed animals had significantly increased circulating E2 when compared to either control group.

CONCLUSIONS

These data indicate that alcohol exposure in utero increases susceptibility to mammary tumorigenesis in adulthood and suggest that alterations in the IGF and E2 systems may play a role in the underlying mechanism.

Magnetic resonance microscopy-based analyses of the brains of normal and ethanol-exposed fetal mice

BACKGROUND

The application of magnetic resonance microscopy (MRM) to the study of normal and abnormal prenatal mouse development has facilitated discovery of dysmorphology following prenatal ethanol insult. The current analyses extend this work, providing a regional brain volume-based description of normal brain growth and illustrating the consequences of gestational day (GD) 10 ethanol exposure in the fetal mouse.

METHODS

To assess normal growth, control C57Bl/6J fetuses collected on GD 16, GD 16.5, and GD 17 were scanned using a 9.4-T magnet, resulting in 29-μm isotropic resolution images. For the ethanol teratogenicity studies, C57Bl/6J dams were administered intraperitoneal ethanol (2.9 g/kg) at 10 days, 0 hr, and 10 days, 4 hr, after fertilization, and fetuses were collected for analyses on GD 17. From individual MRM scans, linear measurements and regional brain volumes were determined and compared.

RESULTS

In control fetuses, each of the assessed brain regions increased in volume, whereas ventricular volumes decreased between GD 16 and GD 17. Illustrating a global developmental delay, prenatal ethanol exposure resulted in reduced body volumes, crown-rump lengths, and a generalized decrease in regional brain volumes compared with GD 17 controls. However, compared with GD 16.5, morphologically matched controls, ethanol exposure resulted in volume increases in the lateral and third ventricles as well as a disproportionate reduction in cortical volume.

CONCLUSIONS

The normative data collected in this study facilitate the distinction between GD 10 ethanol-induced developmental delay and frank dysmorphology. This work illustrates the utility of MRM-based analyses for developmental toxicology studies and extends our knowledge of the stage-dependency of ethanol teratogenesis.

Prenatal psychosocial stress exposure is associated with subsequent working memory performance in young women

The aim of the present study was to examine the association between prenatal psychosocial stress exposure and subsequent prefrontal cortex-dependent working memory performance in human adults. Working memory performance was assessed using an item-recognition task under 10 mg hydrocortisone (cortisol) and placebo conditions in a sample of 32 healthy young women (mean age = 25 +/- 4.34 years) whose mothers experienced a major negative life event during their pregnancy (Prenatal Stress, PS group), and in a comparison group of 27 healthy young women (mean age = 24 +/- 3.4 years). The two groups did not differ in the placebo condition, however, subjects in the PS group showed longer reaction times after hydrocortisone administration compared with subjects in the comparison group (p = .02). These findings provide support for an association between prenatal stress exposure and the potential modulatory effect of cortisol on working memory performance in young adults, which may reflect compromised development of the prefrontal cortex in prenatal life.

Deficits in trace fear conditioning in a rat model of fetal alcohol exposure: dose-response and timing effects

In humans, prenatal alcohol exposure can result in significant impairments in several types of learning and memory, including declarative and spatial memory. Animal models have been useful for confirming that many of the observed effects are the result of alcohol exposure, and not secondary to poor maternal nutrition or adverse home environments. Wagner and Hunt (2006) reported that rats exposed to ethanol during the neonatal period (postnatal days [PDs] 4-9) exhibited impaired trace fear conditioning when trained as adolescents, but were unaffected in delay fear conditioning. The present series of three experiments represent a more detailed analysis of ethanol-induced deficits in trace conditioning. In Experiment 1, the dose of ethanol given to neonates was varied (3.0, 4.0, or 5.0g/kg/day). There was a dose-dependent reduction in trace conditioning, with the poorest performance observed in animals treated with the highest dose. In Experiment 2, it was found that the impairment in trace conditioning resulting from neonatal ethanol exposure was dependent on the duration of the trace interval used for training; less learning was evident in ethanol-exposed animals trained with longer trace interval durations. These results confirm other reports of delay-dependent memory deficits. Finally, Experiment 3 determined that ethanol exposure limited to the first half of the neonatal period (PDs 4-6) was more detrimental to later trace conditioning than exposure during the second half (PDs 7-9). These results support the hypothesis that trace-conditioning impairments resulting from early ethanol exposure are due to the drug's teratogenic effects on the developing hippocampus, as the findings parallel those observed in animals with discrete hippocampal lesions. Comparisons between delay and trace fear-conditioning performance in animals exposed to ethanol during the brain growth spurt provide a model system to study both selective learning impairments and possible treatment approaches for humans with fetal alcohol spectrum disorders.

Executive functioning in children with Fetal Alcohol Spectrum Disorders: profiles and age-related differences

The goal of this project was to examine the profile of executive function (EF) deficits and age-related differences among children with FASD. Twenty-nine children with FASD (8 to 16 years of age) completed 8 tests from the Delis-Kaplan Executive Function System (D-KEFS). They had difficulty on many components of EF including cognitive flexibility, inhibition, some measures of verbal fluency, abstract thinking, deductive reasoning, hypothesis testing, problem solving, and concept formation. A distinctive profile emerged with performance being poorest on the card sorting test and relatively high on category fluency, design fluency, and the tower test, indicating relative strengths on some visual-spatial EF tasks. Older children with FASD showed more difficulty (relative to the norm) on some verbal tests of EF than younger children with FASD, suggesting that difficulty on some verbal EF tasks appears to become more pronounced with increasing age.

Postnatal binge-like alcohol exposure reduces spine density without affecting dendritic morphology in rat mPFC

Among the deficits associated with fetal alcohol syndrome (FAS), cognitive impairments are the most debilitating and permanent. These impairments, including deficits in goal-directed behavior, attention, temporal planning, and other executive functions, could result from damage to the prefrontal cortex (PFC), an area that has not been studied sufficiently in the context of FAS. Neuronal connectivity in this area, as measured by distribution of dendritic spines and the complexity of dendritic tree structure, can be influenced by exogenous variables other than alcohol, and the neuronal connectivity in other brain regions can be affected by alcohol exposure. The goal of this study was to determine whether binge-like alcohol exposure on postnatal days (PD) 4-9 affects dendritic spine density and other dendritic tree parameters in mPFC that could possibly underlie functional damage. Rats were intubated with alcohol [5.25 g/kg/day; alcohol exposed (AE)], sham intubated (SI), or remained with the mother (SC, suckle control) on PD 4-9. Animals were sacrificed between PD 26 and PD 30 and brains were processed for Golgi-Cox staining. Apical dendrite complexity and spine density were evaluated for layer III neurons in the mPFC using NeuroLucida software (MicroBrightField, Inc.). Spine density was significantly decreased in AE animals relative to SI and SC controls, but no differences in dendritic complexity were found across experimental groups. Our findings demonstrate that neonatal alcohol exposure has a persistent effect on the spine density in mPFC that can explain functional deficits in this cortical area.

Computational models of ethanol-induced neurodevelopmental toxicity across species: Implications for risk assessment

Computational, systems-based approaches can provide a quantitative construct for evaluating risk in the context of mechanistic data. Previously, we developed computational models for the rat, mouse, rhesus monkey, and human, describing the acquisition of adult neuron number in the neocortex during the key neurodevelopmental processes of neurogenesis and synaptogenesis. Here we apply mechanistic data from the rat describing ethanol-induced toxicity in the developing neocortex to evaluate the utility of these models for analyzing neurodevelopmental toxicity across species. Our model can explain long-term neocortical neuronal loss in the rodent model after in utero exposure to ethanol based on inhibition of proliferation during neurogenesis. Our human model predicts a significant neuronal deficit after daily peak BECs reaching 10-20 mg/dl, which is the approximate BEC reached after drinking one standard drink within one hour. In contrast, peak daily BECs of 100 mg/dl are necessary to predict similar deficits in the rat. Our model prediction of increased sensitivity of primate species to ethanol-induced inhibition of proliferation is based on application of in vivo experimental data from primates showing a prolonged rapid growth period in the primate versus rodent neuronal progenitor population. To place our predictions into a broader context, we evaluate the evidence for functional low-dose effects across rats, monkeys, and humans. Results from this critical evaluation suggest subtle effects are evident at doses causing peak BECs of approximately 20 mg/dl daily, corroborating our model predictions. Our example highlights the utility of a systems-based modeling approach in risk assessment.

Fetal alcohol syndrome and the developing socio-emotional brain

Fetal alcohol syndrome (FAS) is currently recognized as the most common known cause of mental retardation, affecting from 1 to 7 per 1000 live-born infants. Individuals with FAS suffer from changes in brain structure, cognitive impairments, and behavior problems. Researchers investigating neuropsychological functioning have identified deficits in learning, memory, executive functioning, hyperactivity, impulsivity, and poor communication and social skills in individuals with FAS and fetal alcohol effects (FAE). Investigators using autopsy and brain imaging methods have identified microcephaly and structural abnormalities in various regions of the brain (including the basal ganglia, corpus callosum, cerebellum, and hippocampus) that may account for the neuropsychological deficits. Results of studies using newer brain imaging and analytic techniques have indicated specific alterations (i.e., displacements in the corpus callosum, increased gray matter density in the perisylvian regions, altered gray matter asymmetry, and disproportionate reductions in the frontal lobes) in the brains of individuals prenatally exposed to alcohol, and their relations with brain function. Future research, including using animal models, could help inform our knowledge of brain-behavior relations in the context of prenatal alcohol exposure, and assist with early identification and intervention.

Prenatal ethanol exposure in rats decreases levels of complexin proteins in the frontal cortex

BACKGROUND

Rodents that are prenatally exposed to ethanol have been shown to exhibit a wide range of cognitive deficits, including impairments in memory, attention and executive function. To determine a potential molecular substrate for cognitive dysfunction in adulthood, we measured regional levels of the presynaptic proteins complexin I and II in a rat model of prenatal ethanol exposure, as levels of these proteins are altered in cognitive-related synaptic plasticity.

METHODS

Pregnant female rats received either a liquid ethanol diet (36% ethanol-derived calories) or a liquid control diet (maltose-dextrin isocalorically substituted for ethanol, matched in amount [g/kg body wt/day of gestation] to an ethanol-consuming partner), or were given ad libitum-fed access to standard laboratory chow and water. Levels of complexin I, II and the ubiquitous presynaptic marker synaptophysin were measured in the frontal cortex and hippocampus of adult male offspring, using ELISA.

RESULTS

Prenatal exposure to ethanol did not alter levels of presynaptic proteins in the hippocampus or levels of synaptophysin in the prefrontal cortex. However, rats prenatally exposed to ethanol displayed significantly lower levels of both complexin I and II in the prefrontal cortex compared to control animals.

CONCLUSIONS

These data indicate that prenatal exposure to ethanol is associated with a selective loss of complexin proteins in the frontal cortex. These proteins are known to be important for activity-dependent neurotransmission, and have previously been shown to mediate synaptic plasticity and cognition. These combined findings suggest that further study of complexin proteins as a substrate for cognitive impairment related to prenatal exposure to ethanol is warranted.

Reversal learning after prenatal or early postnatal alcohol exposure in juvenile and adult rats

Learning tasks that require the reversal of a previously learned contingency are disrupted in animals and humans exposed to alcohol during the perinatal period. The current experiments examined how varying the time of alcohol exposure and the age at which subjects were tested would affect the expression of reversal deficits in a T-maze task. Groups of rats were exposed to alcohol from gestational day (GD) 8 to GD20 or from postnatal day (PN) 4 to PN9, and then tested in a spatial reversal task at either PN28 or PN63. Results indicate that exposure to alcohol during the prenatal period did not lead to substantial dose-dependent reversal learning deficits in males or females at either age tested. However, exposure to alcohol during the early postnatal period, a period that corresponds to the third trimester in human neural development, selectively disrupted reversal learning performance in male rats at PN28 but not PN63. Statistically significant sex differences were seen when subjects were tested at PN63. These results demonstrate how the timing of alcohol exposure leads to variability in the age-dependent expression of learning deficits associated with fetal alcohol effects.