Selective and Enduring Deficits in Spatial Learning After Limited Neonatal Binge Alcohol Exposure in Male Rats

Adolescent alcohol and nicotine exposure alters the adult response to alcohol use

Adolescence through young adulthood is a unique period of neuronal development and maturation. Numerous agents can alter this process, resulting in long-term neurological and biological consequences. In the clinical literature, it is frequently reported that adolescent alcohol consumption increases the propensity to develop addictions, including alcohol use disorder (AUD), during adulthood. A general limitation of both clinical and human pre-clinical adolescent alcohol research is the high rate of co-using/abusing more than one drug during adolescence, such as co-using/abusing alcohol with nicotine. A primary goal of basic research is elucidating neuroadaptations produced by adolescent alcohol exposure/consumption that promote alcohol and other drug self-administration in adulthood. The long-term goal is to develop pharmacotherapeutics for the prevention or amelioration of these neuroadaptations. This review will focus on studies that have examined the effects of adolescent alcohol and nicotine exposure on adult alcohol consumption, the hypersensitivity of the mesolimbic dopaminergic system, and enhanced responses not only to alcohol but also to nicotine during adulthood. Again, the long-term goal is to identify potential cholinergic agents to prevent or ameliorate the consequences of, peri-adolescent alcohol abuse.

Ethanol sustains phosphorylated tau protein in the cultured neonatal rat hippocampus: Implications for fetal alcohol spectrum disorders

Fetal Alcohol Spectrum Disorders (FASDs) are comprised of developmental, behavioral, and cognitive abnormalities caused by prenatal alcohol exposure, affecting an estimated 2%-5% of children and costing $4 billion annually in the United States. While some behavioral therapies help, the neurobiological mechanisms that underpin FASDs need further elucidation for development of efficacious pharmacotherapeutics. The role of the tau protein in the hippocampus is likely to be involved. Tau catalyzes microtubule polymerization in developing neurons. However, this function can become disrupted by hyperphosphorylation. Many of the cognitive deficits observed in neurodegenerative tauopathies overlap to some degree with what is observed in juvenile developmental disabilities, such as FASDs (e.g., selective memory, executive dysfunction). Thus, tau protein phosphorylation may be one important mechanism of dysfunction in FASDs. The purpose of this study is to provide an empirical basis for a tauopathic characterization of FASDs. To do so, hippocampal slices were extracted from rats at postnatal day 10 (PND10); hippocampal slices were then exposed to 5 days of 50mM ethanol between 6 days in vitro (DIV) and 11DIV. Immunoblots were taken for Total and p-Tau (Threonine231) at 12DIV and 24DIV. Immunohistochemical fluorescent images were taken for p-Tau (Threonine231) at 12DIV and 24DIV. Separate p-Tau measures were taken for the cornu ammonis 1 (CA1), CA3, and dentate gyrus (DG). Total Tau protein expression remained unchanged between 12DIV and 24DIV regardless of EtOH condition. In the control group, longer DIV was associated with decreased p-Tau. However, in the EtOH-exposed group, p-Tau was sustained across DIV. This is the first study to show that EtOH exposure sustains tau Threonine231 phosphorylation in the perinatal hippocampus regardless of total tau expression. These findings could lead to innovative pharmacotherapeutic targets for the treatment of cognitive deficits seen in FASDs.

Aversive Learning Deficits and Depressive-Like Behaviors Are Accompanied by an Increase in Oxidative Stress in a Rat Model of Fetal Alcohol Spectrum Disorders: The Protective Effect of Rapamycin

Fetal alcohol spectrum disorders (FASDs) are one of the most common consequences of ethanol exposure during pregnancy. In adulthood, these disorders can be manifested by learning and memory deficits and depressive-like behavior. Ethanol-induced oxidative stress may be one of the factors that induces FASD development. The mammalian target of the Rapamycin (mTOR) signaling pathway that acts via two distinct multiprotein complexes, mTORC1 and mTORC2, can affect oxidative stress. We investigated whether mTOR-dependent or mTOR-independent mechanisms are engaged in this phenomenon. Thus, Rapamycin—a selective inhibitor of mTORC1, Torin-2—a non-selective mTORC1/mTORC2 inhibitor, and FK-506—a drug that impacts oxidative stress in an mTOR-independent manner were used. Behavioral tests were performed in adult (PND60-65) rats using a passive avoidance (PA) task (aversive learning and memory) and forced swimming test (FST) (depressive-like behaviors). In addition, the biochemical parameters of oxidative stress, such as lipid peroxidation (LPO), as well as apurinic/apyrimidinic (AP)-sites were determined in the hippocampus and prefrontal cortex in adult (PND65) rats. The rat FASD model was induced by intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). All substances (3 mg/kg) were given 30 min before ethanol. Our results show that neonatal ethanol exposure leads to deficits in context-dependent fear learning and depressive-like behavior in adult rats that were associated with increased oxidative stress parameters in the hippocampus and prefrontal cortex. Because these effects were completely reversed by Rapamycin, an mTORC1 inhibitor, this outcome suggests its usefulness as a preventive therapy in disorders connected with prenatal ethanol exposure.

Apelin-13 attenuates spatial memory impairment by anti-oxidative, anti-apoptosis, and anti-inflammatory mechanism against ethanol neurotoxicity in the neonatal rat hippocampus

It has been shown that alcohol consumption by pregnant women can have detrimental effects on the developing fetus and lead to fetal alcohol spectrum disorders (FASD). Exposure to alcohol in rat pups during this period causes long-term changes in the structure of the animal's hippocampus, leading to impaired hippocampal-related brain functions such as navigation tasks and spatial memory. Apelin-13, a principal neuropeptide with inhibitory effects on neuroinflammation and brain oxidative stress production, has beneficial properties on memory impairment and neuronal injury. The protective effects of apelin-13 have been evaluated on ethanol-related neurotoxicity in the hippocampus of rat pups. Rat pups from 2 until 10 postnatal day, similar to the third trimester of pregnancy in humans, were intubated total daily dose of ethanol (5/27 g/kg/day). Immediately after intubation, 25 and 50 μg/ kg of apelin-13 was injected subcutaneously. By using Morris water maze task, the hippocampus- dependent memory and spatial learning were evaluated 36 days after birth. Then, Immunohistochemical staining was done to determine the levels of GFAP and caspase-3. ELISA assay was also performed to measure both TNF-α and antioxidant enzymes levels. The current study demonstrates that administration of apelin-13 attenuates spatial memory impairment significantly (P < 0.001). After ethanol neurotoxicity, apelin-13 could also increase the catalase level (P < 0.001), activity of total superoxide dismutase as well as glutathione concentration noticeably (P < 0.05). Other impacts of it could be mentioned as attenuating TNF-α production and also preventing lipid peroxidation (P < 0.001). In addition, the results showed that the level of GFAP as a neuroinflammation factor and the number of active caspase-3 positive cells can be decreased by apelin-13 (P < 0.01). Regarding the protective effects of apelin-13 against ethanol-induced neurotoxicity, it is a promising therapeutic choice for FASD; but more studies are needed.

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.

Rapamycin Improves Spatial Learning Deficits, Vulnerability to Alcohol Addiction and Altered Expression of the GluN2B Subunit of the NMDA Receptor in Adult Rats Exposed to Ethanol during the Neonatal Period

Ethanol exposure during pregnancy alters the mammalian target of rapamycin (mTOR) signaling pathway in the fetal brain. Hence, in adult rats exposed to ethanol during the neonatal period, we investigated the influence of rapamycin, an mTOR Complex 1 (mTORC1) inhibitor, on deficits in spatial memory and reversal learning in the Barnes maze task, as well as the ethanol-induced rewarding effects (1.0 or 1.5 g/kg) using the conditioning place preference (CPP) paradigm. Rapamycin (3 and 10 mg/kg) was given before intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). Spatial memory/reversal learning and rewarding ethanol effect were evaluated in adult (PND60–70) rats. Additionally, the impact of rapamycin pre-treatment on the expression of the GluN2B subunit of NMDA receptor in the brain was assessed in adult rats. Our results show that neonatal ethanol exposure induced deficits in spatial memory and reversal learning in adulthood, but the reversal learning outcome may have been due to spatial learning impairments rather than cognitive flexibility impairments. Furthermore, in adulthood the ethanol treated rats were also more sensitive to the rewarding effect of ethanol than the control group. Rapamycin prevented the neonatal effect of ethanol and normalized the GluN2B down-regulation in the hippocampus and the prefrontal cortex, as well as normalized this subunit’s up-regulation in the striatum of adult rats. Our results suggest that rapamycin and related drugs may hold promise as a preventive therapy for fetal alcohol spectrum disorders.

Mechanisms of context conditioning in the developing rat

The article reviews our studies of contextual fear conditioning (CFC) in rats during a period of development---Postnatal Day (PND) 17-33---that represents the late-infant, juvenile, and early-adolescent stages. These studies seek to acquire 'systems level' knowledge of brain and memory development and apply it to a rodent model of Fetal Alcohol Spectrum Disorder (FASD). This rodent model focuses on alcohol exposure from PND4-9, a period of brain development equivalent to the human third trimester, when neocortex, hippocampus, and cerebellum are especially vulnerable to adverse effects of alcohol. Our research emphasizes a variant of CFC, termed the Context Preexposure Facilitation Effect (CPFE, Fanselow, 1990), in which context representations incidentally learned on one occasion are retrieved and associated with immediate shock on a subsequent occasion. These representations can be encoded at the earliest developmental stage but seem not to be retained or retrieved until the juvenile period. This is associated with developmental differences in context-elicited expression, in prefrontal cortex, hippocampus, and amygdala, of immediate early genes (IEGs) that are implicated in long-term memory. Loss-of-function studies establish a functional role for these regions as soon as the CPFE emerges during ontogeny. In our rodent model of FASD, the CPFE is much more sensitive to alcohol dose than other commonly used cognitive tasks. This impairment can be reversed by acute administration during behavioral testing of drugs that enhance cholinergic function. This effect is associated with normalized IEG expression in prefrontal cortex during incidental context learning. In summary, our findings suggest that long-term memory of incidentally-learned context representations depends on prefrontal-hippocampal circuitry that is important both for the normative development of context conditioning and for its disruption by developmental alcohol exposure.

Reduced Hippocampal Volumes Partially Mediate Effects of Prenatal Alcohol Exposure on Spatial Navigation on a Virtual Water Maze Task in Children

BACKGROUND

Prenatal alcohol exposure (PAE) has been linked to poorer performance on the Morris water maze (MWM), a test of spatial navigation in rodents that is dependent on hippocampal functioning. We recently confirmed these findings in children with PAE on a human analog of the MWM, the virtual water maze (VWM). Previous studies have shown that the hippocampus is particularly sensitive to PAE. Our aim was to determine whether hippocampal volume mediates the relation between PAE and virtual navigation.

METHODS

VWM and MRI hippocampal data were collected from 50 right-handed 10-year-old children in a heavily exposed Cape Town, South African sample. PAE data had been collected from their mothers during pregnancy, and the children were examined by expert fetal alcohol spectrum disorder (FASD) dysmorphologists. In the VWM, the participant attempts to learn the location of a hidden platform in a virtual pool of water across a series of learning trials using only distal room cues. Hippocampal volumes were derived using FreeSurfer from MRI scans administered within 1 week of completing the VWM task.

RESULTS

Both the fetal alcohol syndrome (FAS)/partial FAS and nonsyndromal heavy-exposed (HE) groups had smaller hippocampal volumes than controls. PAE was associated with reduced right hippocampal volumes even after control for total intracranial volume (ICV). Hippocampal volume was also positively associated with VWM performance. The relation between PAE and VWM performance was partially mediated by right hippocampal volume but not by total ICV.

CONCLUSIONS

These data confirm previous reports linking PAE to poorer spatial navigation on the VWM and are the first to provide direct evidence that volume reductions in this region partially mediate the relation of FASD diagnosis to place learning, suggesting that PAE specifically impairs the ability to encode the spatial information necessary for successful location of the hidden platform on a navigation task.

Early Postnatal Ethanol Exposure in Mice Induces Sex-Dependent Memory Impairment and Reduction of Hippocampal NMDA-R2B Expression in Adulthood

Drinking alcohol during pregnancy is particularly detrimental for the developing brain and may cause a broad spectrum of cognitive and behavioral impairments, collectively known as fetal alcohol spectrum disorder (FASD). While behavioral abnormalities and brain damage have been widely investigated in animal models of FASD, the sex differences in the vulnerability to perinatal ethanol exposure have received less consideration. Here we investigated the long-term behavioral and molecular effects of acute ethanol-binge like exposure during the early postnatal period (equivalent to the third trimester of human pregnancy) in adult male and female mice. CD1 mice received a single ethanol exposure on P7 and were analyzed starting from P60. We found that ethanol-exposed mice showed increased activity in the open field test and in the plus-maze test, regardless of the sex. Interestingly, only ethanol-exposed adult male mice exhibited memory impairment in the water maze and fear-conditioning tests. Remarkably, hippocampal levels of NMDA-R2B were reduced only in ethanol-exposed male, while total BDNF levels were increased in both male and female ethanol-exposed mice. Our data suggest a different susceptibility of early postnatal ethanol exposure in male and female CD1 mice.

Spatial Navigation in Children and Young Adults with Fetal Alcohol Spectrum Disorders

BACKGROUND

Rodent studies have consistently shown that prenatal alcohol exposure (PAE) impairs performance on the Morris water maze (MWM), a test of spatial navigation. A previous study comparing boys with fetal alcohol syndrome (FAS) to controls found poorer performance on the virtual water maze (VWM), a human analogue of the MWM. We examined PAE effects on virtual navigation in both sexes using the VWM in a moderately exposed Detroit cohort (N = 104; mean = 19.4 year) and a heavily exposed Cape Town, South African cohort (N = 62; mean = 10.4 year).

METHODS

The task requires the participant to learn the location of a hidden platform in a virtual pool of water. The set of acquisition trials requires the participant to learn the location of the hidden platform and to return to that location repeatedly. The single-probe trial requires the participant to return to that location without knowing that the platform has been removed.

RESULTS

No effects of FASD diagnostic group or PAE were detected on virtual navigation in the Detroit moderately exposed cohort. By contrast, in the more heavily exposed Cape Town cohort, the FAS/partial FAS (PFAS) group took longer to locate the hidden platform during acquisition than nonsyndromal heavily exposed (HE) and control groups, an effect that persisted even after controlling for IQ. Among boys, both the FAS/PFAS and HE groups performed more poorly than controls during acquisition, and both boys and girls born to women who binge drank performed more poorly than those born to abstainers/light drinkers. Both amount and frequency of PAE were related to poorer performance during the probe trial at 10 years of age.

CONCLUSIONS

These data demonstrate deficits in spatial navigation among heavily exposed syndromal boys and girls and in nonsyndromal exposed boys.

Periconceptional maternal alcohol consumption leads to behavioural changes in adult and aged offspring and alters the expression of hippocampal genes associated with learning and memory and regulators of the epigenome

Maternal alcohol consumption throughout pregnancy can result in long term behavioural deficits in offspring. However, less is known about the impact of alcohol during the periconceptional period (PC). The aim of this study was to examine the effect of PC ethanol (PC:EtOH) exposure on long term cognitive function; including memory and anxiety. Rats were exposed to a liquid diet containing ethanol (EtOH) (12.5% vol;vol) or a control diet from 4 days prior to mating until day 4 of pregnancy. Separate cohorts of animals were tested at 6 months (adult) or 15-18 months of age (aged). Offspring underwent a series of behavioural tests to assess anxiety, spatial and recognition memory. The hippocampus was collected, and mRNA expression of epigenetic modifiers and genes implicated in learning and memory were examined. PC:EtOH exposure resulted in a subtle anxiety like behaviour in adult female offspring with a significant reduction in directed exploring/head dipping behaviour during holeboard testing. In aged male offspring, PC:EtOH exposure resulted in a tendency for increased directed exploring/head dipping behaviour during holeboard testing. No differences between treatments were observed in the elevated plus maze. Aged female offspring exposed to PC:EtOH demonstrated short term spatial memory impairment (P < 0.05). PC:EtOH resulted in an upregulation of hippocampal mRNA expression of bdnf, grin2a and grin2b at 18 months of age along with increased expression of epigenetic modifiers (dnmt1, dnmt3a and hdac2). In conclusion, PC:EtOH can lead to sex specific anxiety-like behaviour and impairments in spatial memory and altered hippocampal gene expression.

Neonatal ethanol exposure impairs long-term context memory formation and prefrontal immediate early gene expression in adolescent rats

Fetal alcohol exposure leads to severe disruptions in learning and memory involving the hippocampus and prefrontal cortex in humans. Animal model research on FASD has documented impairment of hippocampal neuroanatomy and function but animal studies of cognition involving the prefrontal cortex are sparse. We have found that a variant of contextual fear conditioning in which both the hippocampus and prefrontal cortex is required, the Context Preexposure Facilitation Effect (CPFE), is particularly sensitive to neurobehavioral disruption caused by neonatal ethanol exposure during the third trimester equivalent of human pregnancy in the rat (i.e., PD4-9). In the CPFE, learning about the context, acquiring a context-shock association, and retrieving contextual fear are temporally separated across three days. The current study asked whether neonatal alcohol exposure impairs context learning, consolidation, or retrieval and examined prefrontal and hippocampal molecular signaling as correlates of this impairment. Long-Evans rats that received oral intubation of ethanol (AE; 5.25 g/kg/day, split into two doses) or underwent sham-intubation (SI) from PND4-9 were tested on the CPFE on PD31-33. Extending our previous reports, ethanol abolished both post-shock and retention test freezing in the CPFE. Assays (qPCR) of immediate early gene expression revealed that ethanol disrupted prefrontal but not hippocampal expression of c-Fos, Arc, Egr-1, and Npas4 during context learning. Finally, ethanol-exposed animals were unimpaired in a standard contextual fear conditioning procedure in which learning about the context and acquiring a context-shock association occurs concurrently. These findings implicate impaired prefrontal function in cognitive deficits arising from 3rd-trimester equivalent alcohol exposure in the rat.

Binge Alcohol Exposure Causes Neurobehavioral Deficits and GSK3β Activation in the Hippocampus of Adolescent Rats

Heavy alcohol exposure causes profound damage to the adolescent brain, particularly the hippocampus, which underlie some behavioral deficits. However, the underlying molecular mechanisms remain inconclusive. The current study sought to determine whether binge alcohol exposure affects the hippocampus-related behaviors and key signaling proteins that may mediate alcohol neurotoxicity in adolescent rats. Alcohol exposure reduced the number of both NeuN-positive and doublecortin-positive cells in the hippocampus. Alcohol also induced neurodegeneration which was confirmed by ultrastructural analysis by electronic microscopy and was accompanied with the activation of microglia. Binge alcohol exposure impaired spatial learning and memory which was evaluated by the Morris water maze. However, alcohol did not alter the spontaneous locomotor activity which was determined by the open field test. GSK3β is a multi-function serine/threonine protein kinase regulating both neuronal survival and neurogenesis and plays an important role in various neurodegenerative disorders. We have previously shown that GSK3β is a key mediator of alcohol-induced neuron apoptosis in the developing brain. We showed here binge alcohol exposure caused GSK3β activation by inducing dephosphorylation at Ser9 without affecting the phosphorylation of Tyr216 in the hippocampus. Thus, GSK3β may be involved in binge alcohol exposure-induced neuronal damage to the adolescent hippocampus.

Neonatal Ethanol and Choline Treatments Alter the Morphology of Developing Rat Hippocampal Pyramidal Neurons in Opposite Directions

Some of the neurobehavioral deficits identified in children with Fetal Alcohol Spectrum Disorders (FASDs) have been recapitulated in a binge model of gestational third trimester-equivalent ethanol (EtOH) exposure, in which Sprague-Dawley rats are intragastrically intubated between post-natal day (PD) 4 and PD9 with high doses of EtOH. In this model, the ameliorating effects of choline (Chol) administration on hippocampus-dependent behaviors altered by EtOH have also been extensively documented. In the present study, we investigated the effects of EtOH (5 g/kg/day) and/or Chol (100 mg/kg/day) on morphometric parameters of CA1 pyramidal neurons by Golgi-Cox staining followed by Neurolucida tracing and analysis. We found that EtOH increased apical dendrite complexity in male and female pups neonatally exposed to EtOH. EtOH did not significantly affect basal dendrite parameters in female and male rats. Interestingly, Chol treatments decreased basal dendrites' length, number, and maximal terminal distance in male pups. When pups were co-treated with EtOH and Chol, Chol did not rescue the effect of EtOH. In conclusion, EtOH increases while Chol decreases dendritic length and arborization of hippocampal CA1 neurons in PD9 rats. We hypothesize that developmental EtOH exposure induces a premature maturation of neurons, leading to early restriction of neuronal plasticity while Chol treatments delay the normal program of neuronal maturation and therefore prolong the window of maximal plasticity. Chol does not prevent the effects of developmental alcohol exposure on hippocampal pyramidal neurons' morphology characterized in the present study, although whether prolonged Chol administration after developmental EtOH exposure rectifies EtOH damage remains to be assessed.

Apoptotic cell death and temporal expression of apoptotic proteins Bcl-2 and Bax in the hippocampus, following binge ethanol in the neonatal rat model

BACKGROUND

Binge-like ethanol (EtOH) exposure during the early rat neonatal period results in acute cell loss in specific brain regions, but such acute cell death has not been well established in the hippocampus. Binge alcohol exposure can also result in protein expression changes in the cerebellum that could alter cell fate, but this has not been reported for the hippocampal subregions. This study investigates acute apoptotic cell death in hippocampal regions CA1, CA3, and dentate gyrus (DG) following a binge EtOH exposure on postnatal day (PN) 6, PN8, or PN6 + 8 and the alteration in pro- and anti-apoptotic proteins following a single EtOH binge on PN6.

METHODS

Apoptotic cell death was quantified 12 hours after EtOH binge exposure using the optical fractionator method. Western blot analysis determined expression of pro-apoptotic Bax and anti-apoptotic Bcl-2, 12, 24, and 48 hours after binge EtOH exposure on PN6. The Bcl-2:Bax ratio was used as a measure of vulnerability to apoptosis.

RESULTS

Acute apoptosis increased significantly 12 hours following PN6 or 8 EtOH exposure in CA1, CA3, and DG, but the magnitude of apoptotic cell death was significantly greater in CA1 than in CA3 and DG, which did not differ. Significant cell death was not detected when a PN8 EtOH exposure was preceded by exposure on PN6. Binge EtOH exposure on PN6 resulted in a significant increase in expression of Bcl-2 and the Bcl-2:Bax ratio in the CA1/DG region at 24 hours after EtOH exposure on PN6. The Bcl-2:Bax ratio in the CA3 region was not altered.

CONCLUSIONS

This study shows that repeated binge exposure does not have a cumulative effect on the magnitude of acute apoptotic cell death. This finding may be explained in part by changes in the Bcl-2:Bax ratio after a single binge EtOH exposure.

Neonatal binge alcohol exposure increases microglial activation in the developing rat hippocampus

Aberrant activation of the developing immune system can have long-term negative consequences on cognition and behavior. Teratogens, such as alcohol, activate microglia, the brain's resident immune cells, which could contribute to the lifelong deficits in learning and memory observed in humans with Fetal Alcohol Spectrum Disorders (FASD) and in rodent models of FASD. The current study investigates the microglial response of the brain 24 h following neonatal alcohol exposure (postnatal days (PDs) 4-9, 5.25 g/kg/day). On PD10, microglial cell counts and area of cell territory were assessed using unbiased stereology in the hippocampal subfields CA1, CA3 and dentate gyrus (DG), and hippocampal expression of pro- and anti-inflammatory genes was analyzed. A significant decrease in microglial cell counts in CA1 and DG was found in alcohol-exposed and sham-intubated (SI) animals compared to undisturbed suckle controls (SCs), suggesting overlapping effects of alcohol exposure and intubation alone on the neuroimmune response. Cell territory was decreased in alcohol-exposed animals in CA1, CA3, and DG compared to controls, suggesting the microglia have shifted to a more activated state following alcohol treatment. Furthermore, both alcohol-exposed and SI animals had increased levels of pro-inflammatory cytokines IL-1β, TNF-α, CD11b, and CCL4; in addition, CCL4 was significantly increased in alcohol-exposed animals compared to SI as well. Alcohol-exposed animals also showed increased levels of anti-inflammatory cytokine TGF-β compared to both SI and SCs. In summary, the number and activation of microglia in the neonatal hippocampus are both affected in a rat model of FASD, along with increased gene expression of pro- and anti-inflammatory cytokines. This study shows that alcohol exposure during development induces a neuroimmune response, potentially contributing to long-term alcohol-related changes to cognition, behavior and immune function.

Prenatal ethanol exposure impairs temporal ordering behaviours in young adult rats

Prenatal ethanol exposure (PNEE) causes significant deficits in functional (i.e., synaptic) plasticity in the dentate gyrus (DG) and cornu ammonis (CA) hippocampal sub-regions of young adult male rats. Previous research has shown that in the DG, these deficits are not apparent in age-matched PNEE females. This study aimed to expand these findings and determine if PNEE induces deficits in hippocampal-dependent behaviours in both male and female young adult rats (PND 60). The metric change behavioural test examines DG-dependent deficits by determining whether an animal can detect a metric change between two identical objects. The temporal order behavioural test is thought to rely in part on the CA sub-region of the hippocampus and determines whether an animal will spend more time exploring an object that it has not seen for a larger temporal window as compared to an object that it has seen more recently. Using the liquid diet model of FASD (where 6.6% (v/v) ethanol is provided through a liquid diet consumed ad libitum throughout the entire gestation), we found that PNEE causes a significant impairment in the temporal order task, while no deficits in the DG-dependent metric change task were observed. There were no significant differences between males and females for either task. These results indicate that behaviours relying partially on the CA-region may be more affected by PNEE than those that rely on the DG.

Fetal Alcohol Spectrum Disorder: Potential Role of Endocannabinoids Signaling

One of the unique features of prenatal alcohol exposure in humans is impaired cognitive and behavioral function resulting from damage to the central nervous system (CNS), which leads to a spectrum of impairments referred to as fetal alcohol spectrum disorder (FASD). Human FASD phenotypes can be reproduced in the rodent CNS following prenatal ethanol exposure. Several mechanisms are expected to contribute to the detrimental effects of prenatal alcohol exposure on the developing fetus, particularly in the developing CNS. These mechanisms may act simultaneously or consecutively and differ among a variety of cell types at specific developmental stages in particular brain regions. Studies have identified numerous potential mechanisms through which alcohol can act on the fetus. Among these mechanisms are increased oxidative stress, mitochondrial damage, interference with the activity of growth factors, glia cells, cell adhesion molecules, gene expression during CNS development and impaired function of signaling molecules involved in neuronal communication and circuit formation. These alcohol-induced deficits result in long-lasting abnormalities in neuronal plasticity and learning and memory and can explain many of the neurobehavioral abnormalities found in FASD. In this review, the author discusses the mechanisms that are associated with FASD and provides a current status on the endocannabinoid system in the development of FASD.

The Benefits of Exercise on Structural and Functional Plasticity in the Rodent Hippocampus of Different Disease Models

In this review, the benefits of physical exercise on structural and functional plasticity in the hippocampus are discussed. The evidence is clear that voluntary exercise in rats and mice can lead to increases in hippocampal neurogenesis and enhanced synaptic plasticity which ultimately result in improved performance in hippocampal-dependent tasks. Furthermore, in models of neurological disorders, including fetal alcohol spectrum disorders, traumatic brain injury, stroke, and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease exercise can also elicit beneficial effects on hippocampal function. Ultimately this review highlights the multiple benefits of exercise on hippocampal function in both the healthy and the diseased brain.

Prenatal ethanol exposure impairs spatial cognition and synaptic plasticity in female rats

Chronic prenatal ethanol exposure (CPEE) can impair long-term potentiation (LTP) in the male hippocampus. Sexually specific alterations were frequently reported in female animals that had been prenatally exposed to ethanol. This study aimed to examine the effects of CPEE on spatial learning and memory, as well as on hippocampal synaptic plasticity in female adolescent rats. Female offspring were selected from dams that had been exposed to 4 g/kg/day of ethanol throughout the gestational period. Subsequently, performance in the Morris water maze (MWM) was determined, while LTP and depotentiation were measured in the hippocampal CA3-CA1 pathway. In the behavioral test, the escape latencies in both initial and reversal training stages were significantly prolonged. Interestingly, LTP was considerably enhanced while depotentiation was significantly depressed. Our results suggest a critical role of synaptic plasticity balance, which may prominently contribute to the cognitive deficits present in CPEE offspring.

Significant long-term, but not short-term, hippocampal-dependent memory impairment in adult rats exposed to alcohol in early postnatal life

In rodents, ethanol exposure in early postnatal life is known to induce structural and functional impairments throughout the brain, including the hippocampus. Herein, rat pups were administered one of three ethanol doses over postnatal days (PD) 4-9, a period of brain development comparable to the third trimester of human pregnancy. As adults, control and ethanol rats were trained and tested in a variant of hippocampal-dependent one-trial context fear conditioning. In Experiment 1, subjects were placed into a novel context and presented with an immediate footshock (i.e., within ∼8 sec). When re-exposed to the same context 24 hr later low levels of conditioned freezing were observed. Context pre-exposure 24 hr prior to the immediate shock reversed the deficit in sham-intubated and unintubated control rats, enhancing freezing behavior during the context retention test. Even with context pre-exposure, however, significant dose-dependent reductions in contextual freezing were seen in ethanol rats. In Experiment 2, the interval between context pre-exposure and the immediate shock was shortened to 2 hr, in addition to the standard 24 hr. Ethanol rats trained with the 2 hr, but not 24 hr, interval displayed retention test freezing levels roughly equal to controls. Results suggest the ethanol rats can encode a short-term context memory and associate it with the aversive footshock 2 hr later. In the 24 hr ethanol rats the short-term context memory is poorly transferred or consolidated into long-term memory, we propose, impeding the memory's subsequent retrieval and association with shock.

Effects of one- and three-day binge alcohol exposure in neonatal C57BL/6 mice on spatial learning and memory in adolescence and adulthood

Binge-like alcohol exposure during the early postnatal period in rats and mice causes deficits in spatial learning and memory that persist into adulthood. Wozniak et al. (2004) reported that heavy binge alcohol exposure on postnatal day 7 (PD 7) in C57BL/6 (B6) mice produced profound spatial learning deficits in the Morris water maze when tested in adolescence (P30-39); when tested in adulthood, however, the deficits were greatly attenuated. Using a similar PD 7 binge alcohol exposure paradigm in B6 mice, we tested whether a single-day (PD 7 only) alcohol treatment produced place learning deficits in both adolescence and in adulthood, and further tested whether a more extended (3-day, PD 7-9) alcohol exposure would induce more severe and enduring deficits. B6 mice were given either 2 subcutaneous injections of alcohol (2.5 g/kg each) 2 h apart on PD 7 or on PD 7-9, and compared with controls that received saline vehicle injections and controls that received no injections. The alcohol injections on PD 7 produced average peak blood alcohol concentrations of 472 mg/dL and evoked typical patterns of activated caspase-3-positive neurons in the cortex, hippocampal formation, and striatum 6 h after the last injection. Mice were given standard place training or random location training in the Morris water maze either as adolescents (PD 30-39) or adults (PD 70-79). The adolescents acquired the place learning more slowly than adults, and the alcohol treatments produced only modest place acquisition deficits. In contrast, both the PD7 and the PD 7-9 alcohol treatments resulted in large and significant spatial learning impairments in adults. In contrast to the previous findings of Wozniak et al. (2004), these results indicate that binge alcohol exposure in the 3rd trimester equivalent produces significant and enduring deficits in spatial learning in B6 mice.

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.

Loss of motoneurons in the ventral compartment of the rat hypoglossal nucleus following early postnatal exposure to alcohol

Perinatal alcohol exposure (AE) has multiple detrimental effects on cognitive and various behavioral outcomes, but little is known about its impact on the autonomic functions. In a rat model of fetal alcohol spectrum disorders (FASD), we investigated neurochemical and neuroanatomical alterations in two brainstem nuclei, the hypoglossal nucleus (XIIn) and the dorsal nucleus of the vagus nerve (Xdn). One group of male Sprague-Dawley rats (n=6) received 2.625 g/kg ethanol intragastrically twice daily on postnatal days (PD) 4-9, a period equivalent to the third trimester of human pregnancy, and another group (n=6) was sham-intubated. On PD 18-19, the rats were perfused and medullary sections were immunohistochemically processed for choline acetyltransferase (ChAT) or two aminergic receptors that mediate excitatory drive to motoneurons, α₁-adrenergic (α₁-R) and serotonin 2A (5-HT(2A)-R), and c-Fos. Based on ChAT labeling, AE rats had reduced numbers of motoneurons in the ventral XIIn (XIIn-v; 35.4±1.3 motoneurons per side and section vs. 40.0±1.2, p=0.022), but not in the dorsal XIIn or Xdn. Consistent with ChAT data, both the numbers of α₁-R-labeled motoneurons in the XIIn-v and the area of the XIIn-v measured using 5-HT(2A)-R staining were significantly smaller in AE rats (19.7±1.5 vs. 25.0±1.4, p=0.031 and 0.063 mm² ±0.002 vs. 0.074±0.002, p=0.002, respectively). Concurrently, both 5-HT(2A)-R and c-Fos staining tended to be higher in AE rats, suggesting an increased activation. Thus, postnatal AE causes motoneuronal loss in the XIIn-v. This may compromise upper airway control and contribute to increased risk of upper airway obstructions and sudden infant death in FASD victims.

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.

Involvement of sphingolipids in ethanol neurotoxicity in the developing brain

Ethanol-induced neuronal death during a sensitive period of brain development is considered one of the significant causes of fetal alcohol spectrum disorders (FASD). In rodent models, ethanol triggers robust apoptotic neurodegeneration during a period of active synaptogenesis that occurs around the first two postnatal weeks, equivalent to the third trimester in human fetuses. The ethanol-induced apoptosis is mitochondria-dependent, involving Bax and caspase-3 activation. Such apoptotic pathways are often mediated by sphingolipids, a class of bioactive lipids ubiquitously present in eukaryotic cellular membranes. While the central role of lipids in ethanol liver toxicity is well recognized, the involvement of sphingolipids in ethanol neurotoxicity is less explored despite mounting evidence of their importance in neuronal apoptosis. Nevertheless, recent studies indicate that ethanol-induced neuronal apoptosis in animal models of FASD is mediated or regulated by cellular sphingolipids, including via the pro-apoptotic action of ceramide and through the neuroprotective action of GM1 ganglioside. Such sphingolipid involvement in ethanol neurotoxicity in the developing brain may provide unique targets for therapeutic applications against FASD. Here we summarize findings describing the involvement of sphingolipids in ethanol-induced apoptosis and discuss the possibility that the combined action of various sphingolipids in mitochondria may control neuronal cell fate.

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.

Acute and chronic ethanol intake: effects on spatial and non-spatial memory in rats

Abusive alcohol consumption produces neuronal damage and biochemical alterations in the mammal brain followed by cognitive disturbances. In this work rats receiving chronic and acute alcohol intake were evaluated in a spontaneous delayed non-matching to sample/position test. Chronic alcohol-treated rats had free access to an aqueous ethanol solution as the only available liquid source from the postnatal day 21 to the end of experiment (postnatal day 90). Acute alcoholic animals received an injection of 2 g/kg ethanol solution once per week. Subjects were evaluated in two tests (object recognition and spatial recognition) based on the spontaneous delayed non-matching to sample or to position paradigm using delays of 1 min, 15 min and 60 min. Results showed that chronic and acute alcohol intake impairs the rats' performance in both tests. Moreover, chronic alcohol-treated rats were more altered than acute treated animals in both tasks. Our results support the idea that chronic and acute alcohol administration during postnatal development caused widespread brain damage resulting in behavioral disturbances and learning disabilities.

Housing in environmental complexity following wheel running augments survival of newly generated hippocampal neurons in a rat model of binge alcohol exposure during the third trimester equivalent

BACKGROUND

Binge-like alcohol exposure in neonatal rats during the brain growth spurt causes deficits in adult neurogenesis in the hippocampal dentate gyrus (DG). Previous data from our laboratory demonstrated that 12 days of voluntary wheel running (WR) beginning on postnatal day (PD) 30 significantly increased the number of newly generated cells evident in the DG on PD42 in both alcohol-exposed (AE) and control rats, but 30 days later a sustained beneficial effect of WR was evident only in control rats. This study tested the hypothesis that housing rats in environmental complexity (EC) following WR would promote the survival of the newly generated cells stimulated by WR, particularly in AE rats.

METHODS

On PD4 to 9, pups were intubated with alcohol in a binge-like manner (5.25 g/kg/d), sham-intubated (SI), or reared normally. In Experiment 1, animals were either assigned to WR during PD30 to 42 or socially housed (SH). On PD42, animals were injected with bromodeoxyuridine (BrdU; 200 mg/kg) and perfused 2 hours later to confirm the WR-induced stimulation of proliferation. In Experiment 2, all animals received WR on PD30 to 42 and were injected with BrdU on the last full day of WR. On PD42, animals were randomly assigned either to EC (WR/EC) or to SH (WR/SH) for 30 days and subsequently perfused and brains were processed for immunohistochemical staining to identify BrdU+-, Ki67+-, and BrdU+/NeuN+-labeled cells in DG.

RESULTS

In Experiment 1, WR exposure significantly increased the number of proliferating cells in all 3 postnatal conditions. In Experiment 2, the AE rats given WR/SH had significantly fewer BrdU+ cells compared with control rats given WR/SH. However, WR/EC experience significantly increased the number of surviving BrdU+ cells in both the AE and SI groups compared with WR/SH rats of the same neonatal treatment. Approximately 80% of the surviving BrdU+ cells in the DG across the conditions were colabeled with NeuN.

CONCLUSIONS

WR followed by EC could provide a behavioral model for developing interventions in humans to ameliorate hippocampal-dependent impairments associated with fetal alcohol spectrum disorders.

Behavioral deficits and cellular damage following developmental ethanol exposure in rats are attenuated by CP-101,606, an NMDAR antagonist with unique NR2B specificity

NMDAR-mediated excitotoxicity has been implicated in some of the impairments following fetal ethanol exposure. Previous studies suggest that both neuronal cell death and some of the behavioral deficits can be reduced by NMDAR antagonism during withdrawal, including antagonism of a subpopulation of receptors containing NR2B subunits. To further investigate NR2B involvement, we selected a compound, CP-101,606 (CP) which binds selectively to NR2B/2B stoichiometries, for both in vitro and in vivo analyses. For the in vitro study, hippocampal explants were exposed to ethanol for 10 days and then 24 h following removal of ethanol, cellular damage was quantified via propidium iodide fluorescence. In vitro ethanol withdrawal-associated neurotoxicity was prevented by CP (10 and 25 nM). In vivo ethanol exposure was administered on PNDs 1-7 with CP administered 21 h following cessation. Activity (PNDs 20-21), motor skills (PNDs 31-33), and maze navigation (PNDs 43-44) were all susceptible to ethanol insult; treatment with CP (15 mg/kg) rescued these deficits. Our findings show that CP-101,606, a drug that blocks the NR2B/2B receptor, can reduce some of the damaging effects of "3rd trimester" alcohol exposure in our rodent model. Further work is clearly warranted on the neuroprotective potential of this drug in the developing brain.

Fetal alcohol spectrum disorders: neuropsychological and behavioral features

Heavy prenatal alcohol exposure can cause alterations to the developing brain. The resulting neurobehavioral deficits seen following this exposure are wide-ranging and potentially devastating and, therefore, are of significant concern to individuals, families, communities, and society. These effects occur on a continuum, and qualitatively similar neuropsychological and behavioral features are seen across the spectrum of effect. The term fetal alcohol spectrum disorders (FASD) has been used to emphasize the continuous nature of the outcomes of prenatal alcohol exposure, with fetal alcohol syndrome (FAS) representing one point on the spectrum. This paper will provide a comprehensive review of the neuropsychological and behavioral effects of heavy prenatal alcohol exposure, including a discussion of the emerging neurobehavioral profile. Supporting studies of lower levels of exposure, brain-behavior associations, and animal model systems will be included when appropriate.

Effects of dose and period of neonatal alcohol exposure on the context preexposure facilitation effect

BACKGROUND

Alcohol exposure in the rat on postnatal days (PD) 4 to 9 is known to partially damage the hippocampus and to impair hippocampus-dependent behavioral tasks. We previously reported that PD4 to 9 alcohol exposure eliminated the context preexposure facilitation effect (CPFE) in juvenile rats, a hippocampus-dependent variant of contextual fear conditioning. In the CPFE, context exposure and immediate shock occur on successive occasions and this produces conditioned freezing relative to a control group that is not preexposed to the training context. Here, we extend our earlier findings by examining the effects of neonatal alcohol administered at multiple doses or over different neonatal exposure periods.

METHOD

Rat pups (male and female) were exposed to a single binge dose of alcohol at one of 3 doses (2.75, 4.00, or 5.25 g/kg/d) over PD4 to 9 (Experiment 1) or to 5.25 g over PD4 to 6 or PD7 to 9 (Experiment 2). Sham-intubated (SI) and undisturbed (UD) rats served as controls. On PD31, rats were preexposed to either the training context (Pre) or an alternate context (No-Pre). On PD32, rats received an immediate unsignaled footshock (1.5 mA, 2 seconds) in the training context. Finally, on PD33, all rats were returned to the training context and tested for contextual freezing over a 5-minute period.

RESULTS

Undisturbed- and SI-Pre rats showed the CPFE, i.e., context preexposure facilitated contextual conditioning, relative to their No-Pre counterparts. The immediate shock deficit was present in all No-Pre groups, regardless of previous alcohol exposure. In Experiment 1, blood alcohol level was negatively correlated with contextual freezing. Group 2.75 g-Pre did not differ from controls. Group 4.00 g-Pre froze significantly less than Groups UD- and SI-Pre but more than Group 5.25-Pre, which showed the immediate shock deficit. In Experiment 2, alcohol exposure limited to PD7 to 9, but not PD4 to 6, disrupted the CPFE.

CONCLUSIONS

This is the first demonstration of dose-related impairment on a hippocampus-dependent task produced by neonatal alcohol exposure in the rat. Exposure period effects support previous studies of alcohol and spatial learning. The CPFE is a more sensitive behavioral task that can be used to elucidate developmental alcohol-induced deficits over a range of alcohol doses that are more relevant to human exposure levels.

Toward a neurobehavioral profile of fetal alcohol spectrum disorders

BACKGROUND

A primary goal of recent research is the development of neurobehavioral profiles that specifically define fetal alcohol spectrum disorders (FASD), which may assist differential diagnosis or improve treatment. In the current study, we define a preliminary profile using neuropsychological data from a multisite study.

METHODS

Data were collected using a broad neurobehavioral protocol from 2 sites of a multisite study of FASD. Subjects were children with heavy prenatal alcohol exposure and unexposed controls. The alcohol-exposed group included children with and without fetal alcohol syndrome (FAS). From 547 neuropsychological variables, 22 variables were selected for analysis based on their ability to distinguish children with heavy prenatal alcohol exposure from nonexposed controls. These data were analyzed using latent profile analysis (LPA).

RESULTS

The results indicated that a 2-class model best fit the data. The resulting profile was successful at distinguishing subjects with FAS from nonexposed controls without FAS with 92% overall accuracy; 87.8% of FAS cases and 95.7% of controls were correctly classified. The same analysis was repeated with children with heavy prenatal alcohol exposure but without FAS and nonexposed controls with similar results. The overall accuracy was 84.7%; 68.4% of alcohol-exposed cases and 95% of controls were correctly classified. In both analyses, the profile based on neuropsychological variables was more successful at distinguishing the groups than was IQ alone.

CONCLUSIONS

We used data from 2 sites of a multisite study and a broad neuropsychological test battery to determine a profile that could be used to accurately identify children affected by prenatal alcohol exposure. Results indicated that measures of executive function and spatial processing are especially sensitive to prenatal alcohol exposure.

Variants of contextual fear conditioning are differentially impaired in the juvenile rat by binge ethanol exposure on postnatal days 4-9

Neonatal ethanol exposure in the rat is known to partially damage the hippocampus, but such exposure causes only modest or inconsistent deficits on hippocampus-dependent behavioral tasks. This may reflect variable sensitivity of these tasks or residual function following partial hippocampal injury. The context preexposure facilitation effect (CPFE) is a variant of context conditioning in which context exposure and immediate shock occur on successive occasions. During testing, preexposed rats freeze more than non-preexposed controls. The CPFE is more sensitive to anterograde hippocampal injury than standard contextual fear conditioning (e.g., Rudy JW, O'Reilly RC. Conjunctive representations, the hippocampus, and contextual fear conditioning. Cogn Affect Behav Neurosci 2001;1:66-82). We report that rats exposed to a high binge dose of ethanol (5.25g/kg/day) over postnatal days [PD] 4-9 failed to demonstrate the CPFE when preexposed to the conditioning context on PD31, relative to sham-intubated and undisturbed controls (Experiment 1). Neonatal alcohol disrupted conditioned freezing to a much lesser extent relative to controls when context preexposure was followed by a standard context conditioning trial rather than immediate shock (Experiment 2). Fear conditioning to a discrete auditory cue (tone) was unaffected by neonatal alcohol exposure ruling out possible performance effects (Experiment 3). These findings suggest that the CPFE is an especially sensitive task for detecting hippocampal injury produced by neonatal alcohol. Mixed results with other tasks may reflect residual hippocampal function and/or the use of alternate neurobehavioral systems or "strategies" following alcohol-induced brain damage.

Effects of ethanol on hippocampal function during adolescence: a look at the past and thoughts on the future

It has been demonstrated by several laboratories that ethanol, both acute and chronic, produces effects that are age dependent. Specifically, adolescent rats are less sensitive to the hypnotic and motor-impairing effects of ethanol but are more sensitive to the hypothermic effects of the drug. However, the results on hippocampal function are not as clear. For example, there have been mixed findings regarding adolescent sensitivity of hippocampal-dependent (spatial) memory in response to ethanol. The current review explores the present state of the field as it relates to ethanol's effects in the hippocampus, particularly as it relates to spatial memory. In addition, we review potential neurobiological mechanisms that might underlie the age-dependent effects of ethanol in the hippocampus. Finally, future directions are proposed that will advance the state of the field as it relates to ethanol's effect during this developmental period.

Ethanol acutely inhibits ionotropic glutamate receptor-mediated responses and long-term potentiation in the developing CA1 hippocampus

BACKGROUND

Developmental ethanol (EtOH) exposure damages the hippocampus, causing long-lasting alterations in learning and memory. Alterations in glutamatergic synaptic transmission and plasticity may play a role in the mechanism of action of EtOH. This signaling is fundamental for synaptogenesis, which occurs during the third trimester of human pregnancy (first 12 days of life in rats).

METHODS

Acute coronal brain slices were prepared from 7- to 9-day-old rats. Extracellular and patch-clamp electrophysiological recording techniques were used to characterize the acute effects of EtOH on alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)- and N-methyl-D-aspartate receptor (NMDAR)-mediated responses and long-term potentiation (LTP) in the CA1 hippocampal region.

RESULTS

Ethanol (40 and 80 mM) inhibited AMPAR- and NMDAR-mediated field excitatory postsynaptic potentials (fEPSPs). EtOH (80 mM) also reduced AMPAR-mediated fEPSPs in the presence of an inhibitor of Ca2+ permeable AMPARs. The effect of 80 mM EtOH on NMDAR-mediated fEPSPs was significantly greater in the presence of Mg2+. EtOH (80 mM) neither affected the paired-pulse ratio of AMPAR-mediated fEPSPs nor the presynaptic volley. The paired-pulse ratio of AMPAR-mediated excitatory postsynaptic currents was not affected either, and the amplitude of these currents was inhibited to a lesser extent than that of fEPSPs. EtOH (80 mM) inhibited LTP of AMPAR-mediated fEPSPs.

CONCLUSIONS

Acute EtOH exposure during the third-trimester equivalent of human pregnancy inhibits hippocampal glutamatergic transmission and LTP induction, which could alter synapse refinement and ultimately contribute to the pathophysiology of fetal alcohol spectrum disorder.

The effects of exercise on adolescent hippocampal neurogenesis in a rat model of binge alcohol exposure during the brain growth spurt

Exposure to alcohol during the brain growth spurt results in impaired cognition and learning in adulthood. This impairment is accompanied by permanent structural changes in the hippocampal formation. Exercise improves performance on hippocampal-dependent learning and memory tasks and increases adult neurogenesis in the rat hippocampal dentate gyrus. The present study examined the effects of wheel running during adolescence on dentate gyrus cell proliferation and neurogenesis after postnatal binge-like alcohol exposure. On postnatal days (PD) 4-9, pups were either intubated with alcohol in a binge-like manner, sham intubated, or reared normally. On PD30-42, all animals were randomly assigned to two adolescent conditions: wheel running or inactive control. Animals were injected with BrdU every day between PD32 and PD42 and perfused on PD42 or PD72. In inactive control animals at both PD42 and PD72, cell proliferation and neurogenesis did not differ between postnatal treatment groups. Wheel running significantly increased the number of BrdU-labeled cells on PD42 in all three postnatal treatments. On PD72, only the normal controls showed significant increases in survival of newly generated cells resulting from the wheel running. These results indicate that adolescent wheel running can induce comparable increases in cell proliferation and neurogenesis in alcohol-exposed and control rats, but the long-term survival of those newly generated cells is impaired relative normal controls. Exercise may provide a means to stimulate neurogenesis, with implications for amelioration of hippocampal-dependent learning impairments associated with alcohol exposure. However, benefits requiring long-lasting survival of the newly generated cells will depend on identifying ways to promote survival.

Environmental enrichment alters neurotrophin levels after fetal alcohol exposure in rats

BACKGROUND

Prenatal alcohol exposure causes abnormal brain development, leading to behavioral deficits, some of which can be ameliorated by environmental enrichment. As both environmental enrichment and prenatal alcohol exposure can individually alter neurotrophin expression, we studied the interaction of prenatal alcohol and postweaning environmental enrichment on brain neurotrophin levels in rats.

METHODS

Pregnant rats received alcohol by gavage, 0, 4, or 6 g/kg/d (Zero, Low, or High groups), or no treatment (Naïve group), on gestational days 8 to 20. After weaning on postnatal day 21, offspring were housed for 6 weeks in Isolated, Social, or Enriched conditions. Levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were then measured in frontal cortex, occipital cortex, hippocampus, and cerebellar vermis.

RESULTS

Prenatal alcohol exposure increased NGF levels in frontal cortex (High-dose group) and cerebellar vermis (High- and Low-dose groups); increased BDNF in frontal cortex, occipital cortex and hippocampus (Low-dose groups), and increased NT-3 in hippocampus and cerebellar vermis (High-dose). Environmental enrichment resulted in lower NGF, BDNF, and NT-3 levels in occipital cortex and lower NGF in frontal cortex. The only significant interaction between prenatal alcohol treatment and environment was in cerebellar vermis where NT-3 levels were higher for enriched animals after prenatal alcohol exposure, but not for animals housed under Isolated or Social conditions.

CONCLUSIONS

Both prenatal alcohol exposure and postweaning housing conditions alter brain neurotrophin levels, but the effects appear to be largely independent. Although environmental enrichment can improve functional outcomes, these results do not provide strong support for the hypothesis that rearing in a complex environment ameliorates prenatal alcohol effects on brain neurotrophin levels in rats.

Perinatal alcohol exposure leads to prolonged upregulation of hypothalamic GABA A receptors and increases behavioral sensitivity to gaboxadol

Prenatal alcohol exposure (AE) is associated with lasting abnormalities of sleep and motor development, but the underlying mechanisms are unknown. We hypothesized that AE alters development of GABAergic signaling in the hypothalamic regions important for the control of sleep and motor activity. Alcohol (5.25 g/(kg day)) was administered intragastrically to male rats on postnatal days (PD) 4-9, a period of brain development equivalent to the human third trimester (AE group). Control pups were sham-intubated (S group). Motor activity was monitored on PD27 and 28. On PD29 and 30, GABA A receptor subunit mRNA levels and alpha4 and delta subunit proteins were quantified by RT-PCR and immunoblotting, respectively, in the wake- and motor activity-promoting perifornical (PF) region of the posterior hypothalamus and the sleep-promoting ventrolateral preoptic (VLPO) region of the anterior hypothalamus. Then, in 47-52-day-old rats, motor activity was quantified following administration of GABA A receptor agonist, gaboxadol (5 mg/kg s.c.). In the PF region, mRNA and protein levels for the alpha4 and delta subunits were significantly higher and beta3 and gamma2 subunit mRNAs were also increased in the AE group. In the VLPO region, only the delta subunit mRNA was increased. Spontaneous motor activity was lower and suppressed more by gaboxadol in the AE than S group, and the latency to a transient total loss of activity after gaboxadol was shorter in the AE group. Thus, perinatal AE leads to GABA A receptor overexpression in the vigilance- and motor activity-promoting hypothalamic PF region, with the neurochemical and functional outcomes lasting long beyond the period of the insult.

Dose-dependent deficits in dual interstimulus interval classical eyeblink conditioning tasks following neonatal binge alcohol exposure in rats

BACKGROUND

Neonatal alcohol consumption in rats is widely used to model cerebellar injury arising from 3rd-trimester human fetal alcohol exposure. Binge alcohol exposure of 5 g/kg/day or more over postnatal days (PD) 4 to 9 in rats damages the cerebellum and consequently impairs classical eyeblink conditioning (EBC). The present study sought to identify deficits in EBC using doses lower than those that have been reported previously following alcohol exposure limited to PD4-9. Complex conditioned response (CR) timing tasks utilizing 2 interstimulus intervals (ISIs) were used to test the hypothesis that 3 g/kg/day of alcohol would produce early onset and early peaked CRs, whereas 4 and 5 g/kg/day would impair CR acquisition.

METHODS

Five neonatal treatment groups were used: (1) undisturbed controls, (2) sham intubation controls, (3) 3 g/kg/day of alcohol, (4) 4 g/kg/day of alcohol, or (5) 5 g/kg/day of alcohol. Intubations occurred over PD4-9. In adulthood, rats were trained using ISI discrimination (Experiment 1) or temporal uncertainty (Experiment 2) EBC tasks. In ISI discrimination, 2 distinct conditioned stimuli (CSs; tone and light) are reinforced with a periocular shock unconditioned stimulus (US) at 2 different CS-US intervals. Temporal uncertainty is identical in design with the exception that the same CS is presented at both CS-US intervals.

RESULTS

Alcohol-exposed subjects were impaired in CR acquisition in a task- and dose-dependent fashion. CR deficits were most salient in the peak amplitude measure and occurred in both tasks following alcohol exposure at 4 and 5 g/kg/day. Alcohol at a dosage of 3 g/kg/day impaired CR acquisition only in ISI discrimination. All alcohol doses failed to produce short latency CRs in either task. Alcohol-exposed subjects displayed later-onset and later-peaked CRs to the long-ISI CS in ISI discrimination relative to controls.

CONCLUSIONS

ISI discrimination training may be ideal to identify CR deficits resulting from neonatal exposure to moderate alcohol doses. Applications of this EBC task to humans may enable reliable early identification and diagnosis of individuals with fetal alcohol spectrum disorders.

Binge-like ethanol exposure during the early postnatal period impairs eyeblink conditioning at short and long CS-US intervals in rats

Binge-like ethanol exposure on postnatal days (PD) 4-9 in rodents causes cerebellar cell loss and impaired acquisition of conditioned responses (CRs) during "short-delay" eyeblink classical conditioning (ECC), using optimal (280-350 ms) interstimulus intervals (ISIs). We extended those earlier findings by comparing acquisition of delay ECC under two different ISIs. From PD 4 to 9, rats were intubated with either 5.25 g/kg of ethanol (2/day), sham intubated, or were not intubated. They were then trained either as periadolescents (about PD 35) or as adults (>PD 90) with either the optimal short-delay (280-ms) ISI, a long-delay (880-ms) ISI, or explicitly unpaired CS and US presentations. Neonatal binge ethanol treatment significantly impaired acquisition of conditioning at both ages regardless of ISI, and deficits in the acquisition and expression of CRs were comparable across ISIs. These deficits are consistent with the previously documented ethanol-induced damage to the cerebellar-brainstem circuit essential for Pavlovian ECC.

Neonatal alcohol exposure impairs acquisition of eyeblink conditioned responses during discrimination learning and reversal in weanling rats

Discrimination and reversal of the classically conditioned eyeblink response depends on cerebellar-brainstem interactions with the hippocampus. Neonatal "binge" exposure to alcohol at doses of 5 g/kg/day or more has been shown to impair single-cue eyeblink conditioning in both weanling and adult rats. The present study exposed neonatal rats to acute alcohol intubations across different developmental periods (postnatal day [PND] 4-9 or PND7-9) and tested them from PND26-31 on discriminative classical eyeblink conditioning and reversal. A high dose of alcohol (5 g/kg/day) dramatically impaired conditioning relative to controls when exposure occurred over PND4-9, but produced mild or no impairments when delivered over PND7-9. These findings support previous claims that developmental exposure period plays a critical role in determining the deleterious effects of alcohol on the developing brain. A lower dose of alcohol (4 g/kg/day) delivered from PND4-9--lower than has previously been shown to affect single-cue eyeblink conditioning--also produced deficits on the discrimination task, suggesting that discrimination learning and acquisition of responding to CS+ during reversal may be especially sensitive behavioral indicators of alcohol-induced brain damage in this rat model.

Effect of resource availability on biparental care, and offspring neural and behavioral development in the California mouse (Peromyscus californicus)

Maternal care influences cognitive function in humans, primates and rodents; however, little is known about the effect of biparental care. Environmental factors such as resource availability play an important role in modulating parental investment strategies with subsequent effects on the offspring. Thus, we examined the interaction between foraging demand and biparental care on hippocampal development and novel object recognition in the monogamous, biparental California mouse. We characterized biparental behavior for 15 days in families exposed to either control (ad libitum feeding) or a high-foraging demand across the weaning period. Adult male offspring were then tested in the open field, and for novel object and place recognition, as well as for hippocampal synaptic density and the expression of genes encoding for subunits of the N-methyl-D-aspartate (NMDA) receptor complex, and the postsynaptic density (PSD)-95 scaffolding protein. Under high-foraging demand, the mothers' body weight was decreased at weaning and fathers spent significantly less time in contact with pups. Offspring reared under high-foraging demand weighed less at weaning and, as adults, were more fearful in the open field and showed profound deficits in both novel object and place recognition. While synaptic density and NR1 mRNA expression were unaffected, offspring reared under high-foraging demand showed increased NR2A and decreased NR2B mRNA expression. Further, PSD-95 protein expression was decreased in mice reared under high-foraging demand. Together, the results suggest that resource availability affects biparental investment strategies, with subsequent effects on hippocampal development and novel object recognition in the offspring.