Effects of Developmental Alcohol Exposure on Potentiation and Depression of Visual Cortex Responses

Phosphorylation of CREB at Serine 142 and 143 Is Essential for Visual Cortex Plasticity

The transcription factor cAMP response element-binding protein (CREB) is involved in a myriad of cellular functions in the central nervous system. For instance, the role of CREB via phosphorylation at the amino-acid residue Serine (Ser)133 in expressing plasticity-related genes and activity-dependent neuronal plasticity processes has been extensively demonstrated. However, much less is known about the role of CREB phosphorylation at Ser142 and Ser143. Here, we employed a viral vector containing a dominant negative form of CREB, with serine-to-alanine mutations at residue 142 and 143 to specifically block phosphorylation at both sites. We then transfected this vector into primary neurons in vitro or intracortically injected it into mice in vivo, to test whether these phosphorylation events were important for activity-dependent plasticity. We demonstrated by immunohistochemistry of cortical neuronal cultures that the expression of Arc, a known plasticity-related gene, requires triple phosphorylation of CREB at Ser133, Ser142, and Ser143. Moreover, we recorded visually-evoked field potentials in awake mice before and after a 7-d period of monocular deprivation (MD) to show that, in addition to CREB phosphorylation at Ser133, ocular dominance plasticity (ODP) in the visual cortex also requires CREB phosphorylation at Ser142/143. Our findings suggest that Ser142/143 phosphorylation is an additional post-translational modification of CREB that triggers the expression of specific target genes and activity-dependent neuronal plasticity processes.

Dynamics of microglia and dendritic spines in early adolescent cortex after developmental alcohol exposure

Fetal alcohol spectrum disorder patients suffer from many cognitive disabilities. These include impaired auditory, visual, and tactile sensory information processing, making it more difficult for these patients to learn to navigate social scenarios. Rodent studies have shown that alcohol exposure during the brain growth spurt (BGS) can lead to acute neuronal apoptosis and an immunological response by microglia in the somatosensory cortex. Since microglia have critical physiological functions, including the support of excitatory synapse remodeling via interactions with dendritic spines, we sought to understand whether BGS alcohol exposure has long-term effects on microglial or dendritic spine dynamics. Using in vivo two-photon microscopy in 4-5 week old mice, we evaluated microglial functions such as process motility, the response to tissue injury, and the dynamics of physical interactions between microglial processes and dendritic spines. We also investigated potential differences in the morphology, density, or dynamics of dendritic spines in layer I/II primary sensory cortex of control and BGS alcohol exposed mice. We found that microglial process motility and contact with dendritic spines were not altered after BGS alcohol exposure. While the response of microglial processes toward tissue injury was not significantly altered by prior alcohol exposure, there was a trend suggesting that alcohol early in life may prime microglia to respond more quickly to secondary injury. Spine density, morphology, stability, and remodeling over time were not perturbed after BGS alcohol exposure. We demonstrate that after BGS alcohol exposure, the physiological functions of microglia and excitatory neurons remain intact in early adolescence.

Preclinical methodological approaches investigating of the effects of alcohol on perinatal and adolescent neurodevelopment

Despite much evidence of its economic and social costs, alcohol use continues to increase. Much remains to be known as to the effects of alcohol on neurodevelopment across the lifespan and in both sexes. We provide a comprehensive overview of the methodological approaches to ethanol administration when using animal models (primarily rodent models) and their translational relevance, as well as some of the advantages and disadvantages of each approach. Special consideration is given to early developmental periods (prenatal through adolescence), as well as to the types of research questions that are best addressed by specific methodologies. The zebrafish is used increasingly in alcohol research, and how to use this model effectively as a preclinical model is reviewed as well.

A randomized controlled trial of transcranial direct-current stimulation and cognitive training in children with fetal alcohol spectrum disorder

BACKGROUND

This study was a randomized double-blind sham-controlled trial examining the effects of transcranial direct current stimulation (tDCS) augmented cognitive training (CT) in children with Fetal Alcohol Spectrum Disorders (FASD). Prenatal alcohol exposure has profound detrimental effects on brain development and individuals with FASD commonly present with deficits in executive functions including attention and working memory. The most commonly studied treatment for executive deficits is CT, which involves repeated drilling of exercises targeting the impaired functions. As currently implemented, CT requires many hours and the observed effect sizes are moderate. Neuromodulation via tDCS can enhance brain plasticity and prior studies demonstrate that combining tDCS with CT improves efficacy and functional outcomes. TDCS-augmented CT has not yet been tested in FASD, a condition in which there are known abnormalities in neuroplasticity and few interventions.

METHODS

This study examined the feasibility and efficacy of this approach in 44 children with FASD. Participants were randomized to receive five sessions of CT with either active or sham tDCS targeting the dorsolateral prefrontal cortex, a region of the brain that is heavily involved in executive functioning.

RESULTS

The intervention was feasible and well-tolerated in children with FASD. The tDCS group showed nominally significant improvement in attention on a continuous performance test compared to sham (p = .043). Group differences were observed at the third, fourth and fifth treatment sessions. There was no effect of tDCS on working memory (p = .911). Further, we found no group differences on a trail making task (p = .659) or on the verbal fluency test (p = .826). In the active tDCS group, a significant correlation was observed between improvement in attention scores and decrease in parent-reported attention deficits (p = .010).

CONCLUSIONS

These results demonstrate that tDCS-augmented CT is well tolerated in children with FASD and potentially offers benefits over and above CT alone.

Prenatal Ethanol Exposure and Neocortical Development: A Transgenerational Model of FASD

Fetal Alcohol Spectrum Disorders, or FASD, represent a range of adverse developmental conditions caused by prenatal ethanol exposure (PrEE) from maternal consumption of alcohol. PrEE induces neurobiological damage in the developing brain leading to cognitive-perceptual and behavioral deficits in the offspring. Alcohol-mediated alterations to epigenetic function may underlie PrEE-related brain dysfunction, with these changes potentially carried across generations to unexposed offspring. To determine the transgenerational impact of PrEE on neocortical development, we generated a mouse model of FASD and identified numerous stable phenotypes transmitted via the male germline to the unexposed third generation. These include alterations in ectopic intraneocortical connectivity, upregulation of neocortical Rzrβ and Id2 expression accompanied by both promoter hypomethylation of these genes and decreased global DNA methylation levels. DNMT expression was also suppressed in newborn PrEE cortex, providing further insight into how ethanol perturbs DNA methylation leading to altered regulation of gene transcription. These PrEE-induced, transgenerational phenotypes may be responsible for cognitive, sensorimotor, and behavioral deficits seen in humans with FASD. Thus, understanding the possible epigenetic mechanisms by which these phenotypes are generated may reveal novel targets for therapeutic intervention of FASD and lead to advances in human health.

Proceedings of the 2017 annual meeting of the Fetal Alcohol Spectrum Disorders study group

The 2017 Fetal Alcohol Spectrum Disorders Study Group (FASDSG) meeting was titled "Prenatal alcohol exposure in the context of multiple factors affecting brain development." The theme was reflected in the interactions between members of the Teratology Society and the FASDSG this year. The first keynote speaker, Elaine Faustman, Ph.D., was a liaison between the societies and spoke about systems biology and the multiple genetic and environmental influences on development. The second keynote speaker, Rebecca Knickmeyer, Ph.D., discussed population neuroscience and multiple influences on brain development. The conference presented updates from three government agencies and short presentations by junior and senior investigators showcasing late-breaking FASD research. The conference was capped by Dr. John Hannigan, Ph.D., the recipient of the 2017 Henry Rosett award for career-long contributions to the field.

Developmental alcohol exposure impairs synaptic plasticity without overtly altering microglial function in mouse visual cortex

Fetal alcohol spectrum disorder (FASD), caused by gestational ethanol (EtOH) exposure, is one of the most common causes of non-heritable and life-long mental disability worldwide, with no standard treatment or therapy available. While EtOH exposure can alter the function of both neurons and glia, it is still unclear how EtOH influences brain development to cause deficits in sensory and cognitive processing later in life. Microglia play an important role in shaping synaptic function and plasticity during neural circuit development and have been shown to mount an acute immunological response to EtOH exposure in certain brain regions. Therefore, we hypothesized that microglial roles in the healthy brain could be permanently altered by early EtOH exposure leading to deficits in experience-dependent plasticity. We used a mouse model of human third trimester high binge EtOH exposure, administering EtOH twice daily by subcutaneous injections from postnatal day 4 through postnatal day 9 (P4-:P9). Using a monocular deprivation model to assess ocular dominance plasticity, we found an EtOH-induced deficit in this type of visually driven experience-dependent plasticity. However, using a combination of immunohistochemistry, confocal microscopy, and in vivo two-photon microscopy to assay microglial morphology and dynamics, as well as fluorescence activated cell sorting (FACS) and RNA-seq to examine the microglial transcriptome, we found no evidence of microglial dysfunction in early adolescence. We also found no evidence of microglial activation in visual cortex acutely after early ethanol exposure, possibly because we also did not observe EtOH-induced neuronal cell death in this brain region. We conclude that early EtOH exposure caused a deficit in experience-dependent synaptic plasticity in the visual cortex that was independent of changes in microglial phenotype or function. This demonstrates that neural plasticity can remain impaired by developmental ethanol exposure even in a brain region where microglia do not acutely assume nor maintain an activated phenotype.

What the Spectrum of Microglial Functions Can Teach us About Fetal Alcohol Spectrum Disorder

Alcohol exposure during gestation can lead to severe defects in brain development and lifelong physical, behavioral and learning deficits that are classified under the umbrella term fetal alcohol spectrum disorder (FASD). Sadly, FASD is diagnosed at an alarmingly high rate, affecting 2%–5% of live births in the United States, making it the most common non-heritable cause of mental disability. Currently, no standard therapies exist that are effective at battling FASD symptoms, highlighting a pressing need to better understand the underlying mechanisms by which alcohol affects the developing brain. While it is clear that sensory and cognitive deficits are driven by inappropriate development and remodeling of the neural circuits that mediate these processes, alcohol’s actions acutely and long-term on the brain milieu are diverse and complex. Microglia, the brain’s immune cells, have been thought to be a target for alcohol during development because of their exquisite ability to rapidly detect and respond to perturbations affecting the brain. Additionally, our view of these immune cells is rapidly changing, and recent studies have revealed a myriad of microglial physiological functions critical for normal brain development and long-term function. A clear and complete understanding of how microglial roles on this end of the spectrum may be altered in FASD is currently lacking. Such information could provide important insights toward novel therapeutic targets for FASD treatment. Here we review the literature that links microglia to neural circuit remodeling and provide a discussion of the current understanding of how developmental alcohol exposure affects microglial behavior in the context of developing brain circuits.

The Role of CREB, SRF, and MEF2 in Activity-Dependent Neuronal Plasticity in the Visual Cortex

The transcription factors CREB (cAMP response element binding factor), SRF (serum response factor), and MEF2 (myocyte enhancer factor 2) play critical roles in the mechanisms underlying neuronal plasticity. However, the role of the activation of these transcription factors in the different components of plasticity in vivo is not well known. In this study, we tested the role of CREB, SRF, and MEF2 in ocular dominance plasticity (ODP), a paradigm of activity-dependent neuronal plasticity in the visual cortex. These three proteins bind to the synaptic activity response element (SARE), an enhancer sequence found upstream of many plasticity-related genes (Kawashima et al., 2009; Rodríguez-Tornos et al., 2013), and can act cooperatively to express Arc, a gene required for ODP (McCurry et al., 2010). We used viral-mediated gene transfer to block the transcription function of CREB, SRF, and MEF2 in the visual cortex, and measured visually evoked potentials in awake male and female mice before and after a 7 d monocular deprivation, which allowed us to examine both the depression component (Dc-ODP) and potentiation component (Pc-ODP) of plasticity independently. We found that CREB, SRF, and MEF2 are all required for ODP, but have differential effects on Dc-ODP and Pc-ODP. CREB is necessary for both Dc-ODP and Pc-ODP, whereas SRF and MEF2 are only needed for Dc-ODP. This finding supports previous reports implicating SRF and MEF2 in long-term depression (required for Dc-ODP), and CREB in long-term potentiation (required for Pc-ODP).SIGNIFICANCE STATEMENT Activity-dependent neuronal plasticity is the cellular basis for learning and memory, and it is crucial for the refinement of neuronal circuits during development. Identifying the mechanisms of activity-dependent neuronal plasticity is crucial to finding therapeutic interventions in the myriad of disorders where it is disrupted, such as Fragile X syndrome, Rett syndrome, epilepsy, major depressive disorder, and autism spectrum disorder. Transcription factors are essential nuclear proteins that trigger the expression of gene programs required for long-term functional and structural plasticity changes. Our results elucidate the specific role of the transcription factors CREB, SRF, and MEF2 in the depression and potentiation components of ODP in vivo, therefore better informing future attempts to find therapeutic targets for diseases where activity-dependent plasticity is disrupted.

Effects of Postnatal Enriched Environment in a Model of Parkinson's Disease in Adult Rats

Environmental enrichment is a widespread neuroprotective strategy during development and also in the mature nervous system. Several research groups have described that enriched environment in adult rats has an impact on the progression of Parkinson's disease (PD). The aim of our present study was to examine the effects of early, postnatal environmental enrichment after 6-hydroxydopamine-induced (6-OHDA) lesion of the substantia nigra in adulthood. Newborn Wistar rats were divided into control and enriched groups according to their environmental conditions. For environmental enrichment, during the first five postnatal weeks animals were placed in larger cages and exposed to intensive complex stimuli. Dopaminergic cell loss, and hypokinetic and asymmetrical signs were evaluated after inducing PD with unilateral injections of 6-OHDA in three-month-old animals. Treatment with 6-OHDA led to a significant cell loss in the substantia nigra of control animals, however, postnatal enriched circumstances could rescue the dopaminergic cells. Although there was no significant difference in the percentage of surviving cells between 6-OHDA-treated control and enriched groups, the slightly less dopaminergic cell loss in the enriched group compared to control animals resulted in less severe hypokinesia. Our investigation is the first to provide evidence for the neuroprotective effect of postnatal enriched environment in PD later in life.