Hippocampal Transplants of Fetal GABAergic Progenitors Regulate Adult Neurogenesis in Mice with Temporal Lobe Epilepsy

Abstract

GABAergic interneurons within the dentate gyrus of the hippocampus regulate adult neurogenesis, including proliferation, migration, and maturation of new granule cells born in the subgranular zone (SGZ) of the dentate gyrus (DG). In temporal lobe epilepsy (TLE), some adult-born granule cells migrate ectopically into the hilus, and these cells contribute to increased hyperexcitability and seizures. Yet, transplanting embryonic day 13.5 fetal mouse medial ganglionic eminence (MGE) GABAergic progenitors into the hippocampus of mice with TLE ameliorates spontaneous seizures, due in part, to increased postsynaptic inhibition of adult-born granule cells. Here, we asked whether MGE progenitor transplantation affects earlier stages of adult neurogenesis, by comparing patterns of neurogenesis in naive mice and epileptic (TLE) mice, with or without MGE transplants. In naive and TLE mice, transplanted MGE cells showed comparable migration and process outgrowth. However, in TLE mice with MGE transplants, fewer adult-born Type 3 progenitors migrated ectopically. Furthermore, more Type 3 progenitors survived and migrated into the granule cell layer (GCL), as determined by immunostaining for doublecortin or the thymidine analogue, bromodeoxyuridine (BrdU). To determine whether MGE transplants affected earlier stages of adult neurogenesis, we compared proliferation in the SGZ two-hours after pulse labeling with BrdU in Naive vs. TLE mice and found no significant differences. Furthermore, MGE progenitor transplantation had no effect on cell proliferation in the SGZ. Moreover, when compared to naive mice, TLE mice showed increases in inverted Type 1 progenitors and Type 2 progenitors, concomitant with a decrease in the normally oriented radial Type 1 progenitors. Strikingly, these alterations were abrogated by MGE transplantation. Thus, MGE transplants appear to reverse seizure-induced abnormalities in adult neurogenesis by increasing differentiation and radial migration of adult-born granule cell progenitors, outcomes that may ameliorate seizures.