Abstracts

Rationale: Medial Ganglionic Eminence (MGE) is an established rich source of GABAergic interneurons which migrate to the cortex during early development. To prevent seizures in GAD65 deficient mice (GAD2-/-) that typically exhibit stress-induced seizures, we transplanted MGE cells into the hippocampus of young mice prior to the onset of seizures. Since seizure-prone GABA deficient mice show behavioral deficit in an open field and we also examined their exploratory behavior following cell transplantation . Methods: GAD deficient NOD.129X1-Gad2tmBae/J mice were acquired from Jackson Laboratory. MGE was harvested from E13.5 Actin-GFP heterozygous embryos in L-15 media. Single cell suspensions were made at a concentration of 2x105 cells/ µl. At 5 weeks of age (P35), GAD2-/- mice were injected either with 1 µl of media (control) or with green fluorescent protein (GFP) labeled MGE cells into hilus of the dorsal hippocampus at two points (from bregma, A -2 mm, L -1 mm V -2.5 mm; A -2.5 mm, L -1.5 mm V -2.8 mm). At 24h, 72h, 1 week and 2 weeks post injections, the brains were isolated to check for the viability of transplanted GFP+ cells (n = 2, at each time point). At 1st, 2nd and 3rd weeks after transplantation, mice were placed in the center square of an open field (152.5 cm x 152.5 cm) for 10 minutes to test exploratory behavior and latency to seizure onset. Results: The stress of an open-filed induced seizures in 100% of untreated GAD2 deficient mice, while no seizures occurred in any of the heterozygotes or wildtype mice. The seizures could be induced as early as 4 weeks of life. Two MGE transplanted mice remained seizure-free on repeated provocations, while all media-injected littermate controls (5/5 and historic controls 21/21/) has experienced stress-induced seizures by 8 weeks of life. In the first week after stem cell transplantation, latency to seizure onset in the MGE treated group (n=11) was significantly increased compared to control littermates (n=5) (p= 0.042). No improvement in exploratory behavior was noted in treatment group. Although some GFP-labeled MGE cells were detectable as late as 2 weeks after stem cell transplantation, progressive loss of viable GFP+ cells were apparent at week one and two. Conclusions: GABA-enriched stem cell transplantation rendered 2/11 (18%) GAD2-/-mice seizure-free and significantly lengthened the latency to seizure onset at least one week after injection. Although the efficacy of stem cell transplantation to young adult mice prior to onset of seizure was limited - likely due to limited long-term survival of GABA interneurons -, our result provides a proof of principal that GABA-deficient state can be reversed by stem cell rescue therapy. Reduced GABA inhibition is associated with acquired and genetic human epilepsy as well as with animal models of epilepsy. Preventive therapy that blocks epileptogenesis may be achieved by enhancing GABA neurotransmission and may include stem cell therapy.