L-Type Calcium Channels Contribute to Ethanol-Induced Aberrant Tangential Migration of Primordial Cortical GABAergic Interneurons in the Embryonic Medial Prefrontal Cortex

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Interneuron odyssey: molecular mechanisms of tangential migration

Cortical GABAergic interneurons are critical components of neural networks. They provide local and long-range inhibition and help coordinate network activities involved in various brain functions, including signal processing, learning, memory and adaptative responses. Disruption of cortical GABAergic interneuron migration thus induces profound deficits in neural network organization and function, and results in a variety of neurodevelopmental and neuropsychiatric disorders including epilepsy, intellectual disability, autism spectrum disorders and schizophrenia. It is thus of paramount importance to elucidate the specific mechanisms that govern the migration of interneurons to clarify some of the underlying disease mechanisms. GABAergic interneurons destined to populate the cortex arise from multipotent ventral progenitor cells located in the ganglionic eminences and pre-optic area. Post-mitotic interneurons exit their place of origin in the ventral forebrain and migrate dorsally using defined migratory streams to reach the cortical plate, which they enter through radial migration before dispersing to settle in their final laminar allocation. While migrating, cortical interneurons constantly change their morphology through the dynamic remodeling of actomyosin and microtubule cytoskeleton as they detect and integrate extracellular guidance cues generated by neuronal and non-neuronal sources distributed along their migratory routes. These processes ensure proper distribution of GABAergic interneurons across cortical areas and lamina, supporting the development of adequate network connectivity and brain function. This short review summarizes current knowledge on the cellular and molecular mechanisms controlling cortical GABAergic interneuron migration, with a focus on tangential migration, and addresses potential avenues for cell-based interneuron progenitor transplants in the treatment of neurodevelopmental disorders and epilepsy.

Precocious emergence of cognitive and synaptic dysfunction in 3xTg-AD mice exposed prenatally to ethanol

Alzheimer's disease (AD) is the most common cause of dementia, affecting approximately 50 million people worldwide. Early life risk factors for AD, including prenatal exposures, remain underexplored. Exposure of the fetus to alcohol (ethanol) is not uncommon during pregnancy, and may result in physical, behavioral, and cognitive changes that are first detected during childhood but result in lifelong challenges. Whether or not prenatal ethanol exposure may contribute to Alzheimer's disease risk is not yet known. Here we exposed a mouse model of Alzheimer's disease (3xTg-AD), bearing three dementia-associated transgenes, presenilin1 (PS1M146V), human amyloid precursor protein (APPSwe), and human tau (TauP301S), to ethanol on gestational days 13.5-16.5 using an established binge-type maternal ethanol exposure paradigm. We sought to investigate whether prenatal ethanol exposure resulted in a precocious onset or increased severity of AD progression, or both. We found that a brief binge-type gestational exposure to ethanol during a period of peak neuronal migration to the developing cortex resulted in an earlier onset of spatial memory deficits and behavioral inflexibility in the progeny, as assessed by performance on the modified Barnes maze task. The observed cognitive changes coincided with alterations to both GABAergic and glutamatergic synaptic transmission in layer V/VI neurons, diminished GABAergic interneurons, and increased β-amyloid accumulation in the medial prefrontal cortex. These findings provide the first preclinical evidence for prenatal ethanol exposure as a potential factor for modifying the onset of AD-like behavioral dysfunction and set the groundwork for more comprehensive investigations into the underpinnings of AD-like cognitive changes in individuals with fetal alcohol spectrum disorders.

Fetal alcohol spectrum disorders

Alcohol readily crosses the placenta and may disrupt fetal development. Harm from prenatal alcohol exposure (PAE) is determined by the dose, pattern, timing and duration of exposure, fetal and maternal genetics, maternal nutrition, concurrent substance use, and epigenetic responses. A safe dose of alcohol use during pregnancy has not been established. PAE can cause fetal alcohol spectrum disorders (FASD), which are characterized by neurodevelopmental impairment with or without facial dysmorphology, congenital anomalies and poor growth. FASD are a leading preventable cause of birth defects and developmental disability. The prevalence of FASD in 76 countries is >1% and is high in individuals living in out-of-home care or engaged in justice and mental health systems. The social and economic effects of FASD are profound, but the diagnosis is often missed or delayed and receives little public recognition. Future research should be informed by people living with FASD and be guided by cultural context, seek consensus on diagnostic criteria and evidence-based treatments, and describe the pathophysiology and lifelong effects of FASD. Imperatives include reducing stigma, equitable access to services, improved quality of life for people with FASD and FASD prevention in future generations.