The impact of prenatal alcohol exposure on hippocampal-dependent outcome measures is influenced by prenatal and early-life rearing conditions

Developmental alcohol exposure is exhausting: Sleep and the enduring consequences of alcohol exposure during development

Prenatal alcohol exposure is the leading nongenetic cause of human intellectual impairment. The long-term impacts of prenatal alcohol exposure on health and well-being are diverse, including neuropathology leading to behavioral, cognitive, and emotional impairments. Additionally negative effects also occur on the physiological level, such as the endocrine, cardiovascular, and immune systems. Among these diverse impacts is sleep disruption. In this review, we describe how prenatal alcohol exposure affects sleep, and potential mechanisms of those effects. Furthermore, we outline the evidence that sleep disruption across the lifespan may be a mediator of some cognitive and behavioral impacts of developmental alcohol exposure, and thus may represent a promising target for treatment.

Growth and behavioral differences in a C57BL/6J mouse model of prenatal alcohol exposure

BACKGROUND

Prenatal alcohol exposure (PAE) can produce behavioral deficits in the presence or absence of growth and morphological deficits. Here, we describe a murine PAE model having parallels to the clinical diagnosis of alcohol-related neurodevelopmental deficit (ARND).

METHODS

Pregnant C57BL/6J mice were gavaged with alcohol (ALC, 3 g/kg) or maltodextrin daily on embryonic days (E) E8.5 through E17.5. Blood alcohol levels were 211 ± 14 mg/dL at 30 min post-gavage. Offspring behavior was tested at adolescence.

RESULTS

ALC dams gained less weight during the alcohol exposure period (p = 0.035). ALC male and female pups weighed more than controls at P15 (p ≤ 0.001) and P22 (p ≤ 0.001), but not at P37, perhaps because their dams were pair-housed. During the training session for accelerating rotarod, control offspring trended to stay longer on the rotarod than did ALC offspring [F_(1,54) = 2.892, p = 0.095]. In the Y-maze, ALC offspring had a higher percent alternation than did controls [F_(1,54) = 16.577, p < 0.001], but activity level did not appear to differ. In the fear-conditioning test, there was no ALC effect in the training trial. In the contextual test, there was a group × minute effect for males [F_(4,120) = 2.94, p = 0.023], and ALC trended to freeze less than controls in minute 1 (p = 0.076) and froze less in minute 2 (p = 0.02). In the cue test, there was a trend for a group-sex interaction [F_(1,53) = 3.008, p = 0.089] on overall freezing, such that ALC males (p < 0.05) again froze less than control males, whereas ALC females (p < 0.05) froze more than control females.

CONCLUSIONS

This mouse model of PAE, using a repeated intermediate exposure, produces modest behavioral impairments that are consistent along the continuum of PAE models, including deficits in associative memory and hyper-responsivity. The lack of growth or morphological deficits suggests these mice may model aspects of ARND.

Sex-specific effect of prenatal alcohol exposure on N-methyl-D-aspartate receptor function in orbitofrontal cortex pyramidal neurons of mice

BACKGROUND

Alcohol consumption during pregnancy can produce behavioral and cognitive deficits that persist into adulthood. These include impairments in executive functions, learning, planning, and cognitive flexibility. We have previously shown that moderate prenatal alcohol exposure (PAE) significantly impairs reversal learning, a measure of flexibility mediated across species by different brain areas that include the orbital frontal cortex (OFC). Reversal learning is likewise impaired by genetic or pharmacological inactivation of GluN2B subunit-containing N-methyl-D-aspartate receptors (NMDARs). In the current study, we tested the hypothesis that moderate PAE persistently alters the number and function of GluN2B subunit-containing NMDARs in OFC pyramidal neurons of adult mice.

METHODS

We used a rodent model of fetal alcohol spectrum disorders and left offspring undisturbed until adulthood. Using whole-cell, patch-clamp recordings, we assessed NMDAR function in slices from 90- to 100-day-old male and female PAE and control mice. Pharmacologically isolated NMDA receptor-mediated evoked excitatory postsynaptic currents (NMDA-eEPSCs) were recorded in the absence and presence of the GluN2B antagonist, Ro25-6981(1 µM). In a subset of littermates, we evaluated the level of GluN2B protein expression in the synaptic fraction using Western blotting technique.

RESULTS

Our results indicate that PAE females show significantly larger (~23%) NMDA-eEPSC amplitudes than controls, while PAE induced a significant decrease (~17%) in NMDA-eEPSC current density of pyramidal neurons recorded in slices from male mice. NMDA-eEPSC decay time was not affected in PAE-exposed mice from either sex. The contribution of GluN2B subunit-containing NMDARs to the eEPSCs was not significantly altered by PAE. Moreover, there were no significant changes in protein expression in the synaptic fraction of either PAE males or females.

CONCLUSIONS

These findings suggest that low-to-moderate PAE modulates NMDAR function in pyramidal neurons in a sex-specific manner, although we did not find evidence that the effect is mediated by dysfunction of synaptic GluN2B subunit-containing NMDARs.

Post-exposure environment modulates long-term developmental ethanol effects on behavior, neuroanatomy, and cortical oscillations

Developmental exposure to ethanol has a wide range of anatomical, cellular, physiological and behavioral impacts that can last throughout life. In humans, this cluster of effects is termed fetal alcohol spectrum disorder and is highly prevalent in western cultures. The ultimate expression of the effects of developmental ethanol exposure however can be influenced by post-exposure experience. Here we examined the effects of developmental binge exposure to ethanol (postnatal day 7) in C57BL/6By mice on a specific cohort of inter-related long-term outcomes including contextual memory, hippocampal parvalbumin-expressing neuron density, frontal cortex oscillations related to sleep-wake cycling including delta oscillation amplitude and sleep spindle density, and home-cage behavioral activity. When assessed in adults that were raised in standard housing, all of these factors were altered by early ethanol exposure compared to saline controls except home-cage activity. However, exposure to an enriched environment and exercise from weaning to postnatal day 90 reversed most of these ethanol-induced impairments including memory, CA1 but not dentate gyrus PV+ cell density, delta oscillations and sleep spindles, and enhanced home-cage behavioral activity in Saline- but not EtOH-treated mice. The results are discussed in terms of the inter-dependence of diverse developmental ethanol outcomes and potential mechanisms of post-exposure experiences to regulate those outcomes.

State-of-the-Science Review of Non-Chemical Stressors Found in a Child's Social Environment

Background: Children are exposed to chemical and non-chemical stressors from their built, natural, and social environments. Research is needed to advance our scientific understanding of non-chemical stressors, evaluate how they alter the biological response to a chemical stressor, and determine how they impact children’s health and well-being. To do this, we conducted a state-of-the-science review of non-chemical stressors found in a child’s social environment. Methods: Studies eligible for inclusion in this review were identified through a search of the peer-reviewed literature using PubMed and PsycINFO. Combinations of words associated with non-chemical stressors and children were used to form search strings. Filters were used to limit the search to studies published in peer-reviewed journals from 2000–2016 and written in English. Publications found using the search strings and filters went through two rounds of screening. Results: A total of 146 studies met the inclusion criteria. From these studies, 245 non-chemical stressors were evaluated. The non-chemical stressors were then organized into 13 general topic areas: acculturation, adverse childhood experiences, economic, education, family dynamics, food, greenspace, neighborhood, social, stress, urbanicity, violence, and other. Additional information on health outcomes, studies evaluating both chemical and non-chemical stressors, and animal studies are provided. This review provides evidence that non-chemical stressors found in a child’s social environment do influence their health and well-being in both beneficial (e.g., salutatory effects of greenspace and social support) and adverse (e.g., poor relationships between health and selected non-chemical stressors such as economics, educational attainment, exposure to violence, stress) ways. Conclusions: This literature review identified a paucity of studies addressing the combined effects of chemical and non-chemical stressors and children’s health and well-being. This literature review was further complicated by inconsistencies in terminology, methodologies, and the value of non-chemical stressor research in different scientific disciplines. Despite these limitations, this review showed the importance of considering non-chemical stressors from a child’s social environment when addressing children’s environmental health considerations.

Increased Maternal Care Rescues Altered Reinstatement Responding Following Moderate Prenatal Alcohol Exposure

BACKGROUND

Fetal alcohol spectrum disorders (FASD) commonly include deficits in learning, memory, and executive control that can have a severe negative impact on quality of life across the life span. It is still unclear how prenatal alcohol exposure (PAE) affects executive control processes, such as control over reward seeking, that lead to inappropriate behavior later in life. Learning and reinstatement of a previously learned response after extinction is a simple, well-validated measure of both acquisition of a rewarded instrumental response and sensitivity to reward and reward-associated cues. We investigated the effects of PAE on learning, extinction, and reinstatement of a simple instrumental response for food reward. Next, we assessed the effectiveness of an early intervention, communal nest (CN) housing, on increased reinstatement of an extinguished response seen after PAE.

METHODS

To assess the effects of PAE on control over reward seeking, we tested male and female PAE and saccharine (SAC) controls raised in a standard nest (SN) on the acquisition, extinction, and food reward-induced reinstatement of an instrumental response utilizing a touch screen-based paradigm. Next, in order to examine the effects of an early-life intervention on these behaviors, we tested PAE and SAC mice raised in a CN early-life environment on these behaviors.

RESULTS

PAE mice readily acquired and extinguished a simple touch response to a white square stimulus. However, PAE mice showed significantly increased and persistent reinstatement compared to controls. Increased maternal care via rearing in CN slowed acquisition and sped extinction learning and rescued the significantly increased reinstatement responding in PAE mice.

CONCLUSIONS

Together these results demonstrate that even moderate PAE is sufficient to alter control over reward seeking as measured by reinstatement. Importantly, an early-life intervention previously shown to improve cognitive outcomes in PAE mice was sufficient to ameliorate this effect.

Interactive effects of prenatal alcohol exposure and chronic stress in adulthood on anxiety-like behavior and central stress-related receptor mRNA expression: Sex- and time-dependent effects

Children and adults prenatally exposed to alcohol show higher rates of mental health problems than unexposed individuals, with depression and anxiety being among the more commonly encountered disorders. Previous studies in rats showed that prenatal alcohol exposure (PAE) can indeed increase depressive- and anxiety-like behavior in adulthood; however, depression and anxiety are often observed in the context of stress and/or a dysregulated stress response system (the hypothalamic-pituitary-adrenal [HPA] axis). PAE can dysregulate the HPA axis, resulting in hyperresponsivity to stress. In turn, this may predispose individuals prenatally exposed to alcohol to the adverse effects of stress compared to unexposed individuals. We have shown previously that PAE animals may be more sensitive to the effects of chronic stress on behavior, showing increased anxiety- and depressive-like behavior following chronic unpredictable stress (CUS) exposure. Here, we investigated the independent and interactive effects of PAE and adult CUS on anxiety-like behavior and receptor systems (corticotropin-releasing hormone receptor type 1 [CRHR1], mineralocorticoid receptor [MR], and glucocorticoid receptor [GR]), and underlying stress and emotional regulation, and whether exposure to CUS differentially results in immediate or delayed effects. Adult male and female offspring from PAE, pair-fed (PF), and ad libitum-fed control (C) dams were exposed to either 10 days of CUS or left undisturbed. Behavioral testing began 1 or 14 days post-CUS, and brains were collected following testing. Anxiety-like behaviors were evaluated using the open field, elevated plus maze and dark-light emergence tests. CRHR1, MR, and GR mRNA expression were assessed in the medial prefrontal cortex (mPFC), amygdala, and hippocampal formation, brain areas key to both stress and emotional regulation. We found that PAE differentially increased anxiety-like behavior and altered GR mRNA in males and females compared to their control counterparts. Furthermore, depending on the timing of testing, CUS unmasked alterations in GR and CRHR1 mRNA expression in the mPFC and amygdala in PAE males, and MR mRNA in the hippocampal formation in PAE females compared to their C counterparts. Overall, the changes observed in these receptor systems may underlie the increase in anxiety-like behavior following PAE and CUS exposure in adulthood. That CUS differentially affected brain and behavioral outcome of PAE and C animals, and did so in a sexually-dimorphic manner, has important implications for understanding the etiology of psychopathology in individuals prenatally exposed to alcohol.

Sex-specific deficits in biochemical but not behavioral responses to delay fear conditioning in prenatal alcohol exposure mice

BACKGROUND

Studies in clinical populations and preclinical models have shown that prenatal alcohol exposure (PAE) is associated with impairments in the acquisition, consolidation and recall of information, with deficits in hippocampal formation-dependent learning and memory being a common finding. The glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and extracellular signal-regulated kinase 2 (ERK2) are key regulators of hippocampal formation development, structure and functioning and, thus, are potential mediators of PAE's effects on this brain region. In the present studies, we employed a well-characterized mouse model of PAE to identify biochemical mechanisms that may underlie activity-dependent learning and memory deficits associated with PAE.

METHODS

Mouse dams consumed either 10% (w/v) ethanol in 0.066% (w/v) saccharin (SAC) or 0.066% (w/v) SAC alone using a limited (4-h) access, drinking-in-the-dark paradigm. Male and female offspring (∼180-days of age) were trained using a delay conditioning procedure and contextual fear responses (freezing behavior) were measured 24 h later. Hippocampal formation tissue and blood were collected from three behavioral groups of animals: 20 min following conditioning (conditioning only group), 20 min following the re-exposure to the context (conditioning plus re-exposure group), and behaviorally naïve (naïve group) mice. Plasma corticosterone levels were measured by enzyme immunoassay. Immunoblotting techniques were used to measure protein levels of the GR, MR, ERK1 and ERK2 in nuclear and membrane fractions prepared from the hippocampal formation.

RESULTS

Adult SAC control male and female mice displayed similar levels of contextual fear. However, significant sex differences were observed in freezing exhibited during the conditioning session. Compared to same-sex SAC controls, male and female PAE mice demonstrated context fear deficits While plasma corticosterone concentrations were elevated in PAE males and females relative to their respective SAC naïve controls, plasma corticosterone concentrations in the conditioning only and conditioning plus re-exposure groups were similar in SAC and PAE animals. Relative to the respective naïve group, nuclear GR protein levels were increased in SAC, but not PAE, male hippocampal formation in the conditioning only group. In contrast, no difference was observed between nuclear GR levels in the naïve and conditioning plus re-exposure groups. In females, nuclear GR levels were significantly reduced by PAE but there was no effect of behavioral group or interaction between prenatal treatment and behavioral group. In males, nuclear MR levels were significantly elevated in the SAC conditioning plus re-exposure group compared to SAC naïve mice. In PAE females, nuclear MR levels were elevated in both the conditioning only and conditioning plus re-exposure groups relative to the naïve group. Levels of activated ERK2 (phospho-ERK2 expressed relative to total ERK2) protein were elevated in SAC, but not PAE, males following context re-exposure, and a significant interaction between prenatal exposure group and behavioral group was found. No main effects or interactions of behavioral group and prenatal treatment on nuclear ERK2 were found in female mice. These findings suggest a sex difference in which molecular pathways are activated during fear conditioning in mice.

CONCLUSIONS

In PAE males, the deficits in contextual fear were associated with the loss of responsiveness of hippocampal formation nuclear GR, MR and ERK2 to signals generated by fear conditioning and context re-exposure. In contrast, the contextual fear deficit in PAE female mice does not appear to be associated with activity-dependent changes in GR and MR levels or ERK2 activation during training or memory recall, although an overall reduction in nuclear GR levels may play a role. These studies add to a growing body of literature demonstrating that, at least partially, different mechanisms underlie learning, memory formation and memory recall in males and females and that these pathways are differentially affected by PAE.

Moderate developmental alcohol exposure reduces repetitive alternation in a zebrafish model of fetal alcohol spectrum disorders

The damaging effects of alcohol on a developing fetus are well known and cause a range of conditions known as fetal alcohol spectrum disorder (FASD). High levels of alcohol exposure lead to physical deformity and severe cognitive deficits, but more moderate exposure leads to a range of subtle cognitive effects such as reduced social behavior, higher propensity to develop addictions, and reduced spatial working memory. Previous studies have demonstrated that following exposure to relatively low levels of ethanol during early brain development (equivalent in humans to moderate exposure) zebrafish display a range of social and behavioral differences. Here, our aim was to test the hypothesis that moderate developmental ethanol exposure would affect aspects of learning and memory in zebrafish. In order to do this, we exposed zebrafish embryos to 20 mM [0.12% v/v] ethanol from 2 to 9 dpf to model the effects of moderate prenatal ethanol (MPE) exposure. At 3 months old, adult fish were tested for appetitive and aversive learning, and for spatial alternation in a novel unconditioned y-maze protocol. We found that MPE did not affect appetitive or aversive learning, but exposed-fish showed a robust reduction in repetitive alternations in the y-maze when compared to age matched controls. This study confirms that moderate levels of ethanol exposure to developing embryos have subtle effects on spatial working memory in adulthood. Our data thus suggest that zebrafish may be a promising model system for studying the effects of alcohol on learning and decision-making, but also for developing treatments and interventions to reduce the negative effects of prenatal alcohol.

Impact of adolescent stress on the expression of stress-related receptors in the hippocampus of animals exposed to alcohol prenatally

Many functions of the hippocampus are affected by prenatal alcohol exposure (PAE). In particular, dysregulation of the stress response is especially important because individuals with PAE carry increased risks for exposure to stressful environments throughout life. Little is known, though, about how adolescent stress in the context of PAE-related stress system dysregulation may further alter hippocampal development. Here, we investigate the short- and long-term effects of adolescent chronic mild stress (CMS) on mRNA expression of stress-related mineralocorticoid (MR), glucocorticoid (GR), and type 1 CRH (CRHR1) receptors in the dorsal and ventral hippocampal formation of PAE and control rats. Our results indicate that PAE affects the expression of stress-related receptors in the hippocampus; however, PAE effects were more prominent during adolescence, as MR and CRHR1 mRNA expression were altered in both male and female PAE animals, with GR mRNA expression alterations observed only in PAE female. In adulthood, the effects of PAE were restricted to alterations in CRHR1 mRNA expression in females, while there were no effects in males. In contrast, the effects of adolescent CMS were more pronounced in adulthood, long after stress exposure termination. Importantly, PAE animals were less responsive to adolescent CMS, with effects only on CRHR1 in PAE animals compared to the altered MR, GR, and CRHR1 mRNA expression observed in controls. Together, our results show that PAE and adolescent CMS induce dynamic alterations in the expression of stress-related receptors in the hippocampal formation that manifest differently depending on the age and sex of the animal.