Gestational exposure to ethanol has been reported to alter the disposition of tangentially migrating GABAergic cortical interneurons, but much remains to be elucidated. Here we first established the migration of interneurons as a proximal target of ethanol by limiting ethanol exposure in utero to the gestational window when tangential migration is at its height. We then asked whether the aberrant tangential migration of GABAergic interneurons persisted as an enduring interneuronopathy in the medial prefrontal cortex (mPFC) later in the life of offspring prenatally exposed to ethanol. Time pregnant mice with Nkx2.1Cre/Ai14 embryos harboring tdTomato-fluorescent medial ganglionic eminence (MGE)-derived cortical GABAergic interneurons were subjected to a 3 day binge-type 5% w/w ethanol consumption regimen from embryonic day (E) 13.5-16.5, spanning the peak of corticopetal interneuron migration in the fetal brain. Our binge-type regimen increased the density of MGE-derived interneurons in the E16.5 mPFC. In young adult offspring exposed to ethanol in utero, this effect persisted as an increase in the number of mPFC layer V parvalbumin-immunopositive interneurons. Commensurately, patchclamp recording in mPFC layer V pyramidal neurons uncovered enhanced GABA-mediated spontaneous and evoked synaptic transmission, shifting the inhibitory/excitatory balance toward favoring inhibition. Furthermore, young adult offspring exposed to the 3 day binge-type ethanol regimen exhibited impaired reversal learning in a modified Barnes maze, indicative of decreased PFC-dependent behavioral flexibility, and heightened locomotor activity in an open field arena. Our findings underscore that aberrant neuronal migration, inhibitory/excitatory imbalance, and thus interneuronopathy contribute to indelible abnormal cortical circuit form and function in fetal alcohol spectrum disorders.

Background Exposure to ethanol in utero alters the disposition of tangentially migrating GABAergic interneurons in the fetal brain. The medial ganglionic eminence (MGE) gives rise to a large portion of cortical GABAergic interneurons, including the parvalbumin-expressing interneurons that shape and contribute to inhibitory/excitatory (I/E) balance of the intracortical circuit. Here, we investigated in the mouse medial prefrontal cortex (mPFC) the hypothesis that low levels of maternal ethanol consumption from closure of the neural tube embryonic day(E) 9.5 until birth, results in an enduring interneuronopathy. Methods Pregnant mice were subjected to a 2% w/w ethanol consumption regimen starting at neural tube closure and ending at parturition. Neurogenesis in the MGE was assessed by BrdU-immunofluorescence at E12.5. The count and distribution of parvalbumin-expressing interneurons were determined in adult animals, and patch clamp electrophysiology was performed to determine GABAergic function and I/E balance. Open field behavior in adult mice was assessed to determine whether the ethanol-exposed cohort displayed a lasting alteration in exploratory behavior. Results In embryos exposed to ethanol in utero, we found increased BrdU labeling in the MGE, pointing to increased neurogenesis. Adult mice prenatally exposed to ethanol were hyperactive, and this was associated with an increase in parvalbumin-expressing GABAergic interneurons in the mPFC. In addition, prenatal ethanol exposure altered the balance between spontaneous inhibitory and excitatory synaptic input and attenuated GABAergic tone in layer V mPFC pyramidal neurons in juvenile mice. Conclusion These findings underscore that altered migration of GABAergic interneurons contributes to the ethanol-induced aberration of cortical development and that these effects persist into adulthood as altered cortical form and function.

Prenatal exposure to ethanol induces aberrant tangential migration of corticopetal GABAergic interneurons, and long-term alterations in the form and function of the prefrontal cortex. We have hypothesized that interneuronopathy contributes significantly to the pathoetiology of fetal alcohol spectrum disorders (FASD). Activity-dependent tangential migration of GABAergic cortical neurons is driven by depolarizing responses to ambient GABA present in the cortical enclave. We found that ethanol exposure potentiates the depolarizing action of GABA in GABAergic cortical interneurons of the embryonic mouse brain. Pharmacological antagonism of the cotransporter NKCC1 mitigated ethanol-induced potentiation of GABA depolarization and prevented aberrant patterns of tangential migration induced by ethanol in vitro. In a model of FASD, maternal bumetanide treatment prevented interneuronopathy in the prefrontal cortex of ethanol exposed offspring, including deficits in behavioral flexibility. These findings position interneuronopathy as a mechanism of FASD symptomatology, and posit NKCC1 as a pharmacological target for the management of FASD.