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Impaired GABA-mediated neurotransmission has been implicated in many neurologic diseases, including epilepsy, intellectual disability and psychiatric disorders. We found that inhibitory neuron transplantation into the hippocampus of adult mice with confirmed epilepsy at the time of grafting markedly reduced the occurrence of electrographic seizures and restored behavioral deficits in spatial learning, hyperactivity and the aggressive response to handling. In the recipient brain, GABA progenitors migrated up to 1,500 μm from the injection site, expressed genes and proteins characteristic for interneurons, differentiated into functional inhibitory neurons and received excitatory synaptic input. In contrast with hippocampus, cell grafts into basolateral amygdala rescued the hyperactivity deficit, but did not alter seizure activity or other abnormal behaviors. Our results highlight a critical role for interneurons in epilepsy and suggest that interneuron cell transplantation is a powerful approach to halting seizures and rescuing accompanying deficits in severely epileptic mice.

Hemizygous mutations in the human gene encoding platelet-activating factor acetylhydrolase IB subunit alpha (Pafah1b1), also called Lissencephaly-1, can cause classical lissencephaly, a severe malformation of cortical development. Children with this disorder suffer from deficits in neuronal migration, severe intellectual disability, intractable epilepsy and early death. While many of these features can be reproduced in Pafah1b1^+/- mice, the impact of Pafah1b1^+/- on the function of individual subpopulations of neurons and ultimately brain circuits is largely unknown. Here, we show tangential migration of young GABAergic interneurons into the developing hippocampus is slowed in Pafah1b1^+/- mice. Mutant mice had a decreased density of parvalbumin- and somatostatin-positive interneurons in dentate gyrus, but no change in density of calretinin interneurons. Whole-cell patch-clamp recordings revealed increased excitatory and decreased inhibitory synaptic inputs onto granule cells of Pafah1b1^+/- mice. Mutant animals developed spontaneous electrographic seizures, as well as long-term deficits in contextual memory. Our findings provide evidence of a dramatic shift in excitability in the dentate gyrus of Pafah1b1^+/- mice that may contribute to epilepsy or cognitive impairments associated with lissencephaly.