Properties of gamma frequency oscillatory activity induced in hippocampal slices from the adult GAD67-GFP (Deltaneo) mouse.

The green fluorescent protein (GFP)-linked expression of protein in transgenic mice provides an ideal tool for the correlation of structure and function in the CNS. An important target of study is the role of GABAergic neurons in oscillatory activity in the hippocampus, and this would be facilitated with transgenic mice in which GFP is linked to the expression of GABA markers. One such mouse is the GAD67-GFP (Deltaneo), and here we compare the properties of kainate- and carbachol-induced oscillatory activity generated in CA3 of hippocampal slices from heterozygous GAD67-GFP (Deltaneo) mice and wild type litter mates. For both paradigms and in both mouse preparations oscillations were generated in the 20-30Hz range, and for the kainate-, but not the carbachol-induced oscillations, there was a small but significant difference in peak frequency of the oscillations between GAD67-GFP (Deltaneo) mice (28.4+/-2.2Hz) and wild type mice (25+/-1.6Hz). For both oscillatory paradigms there was no significant difference between mouse strains in area power of the oscillatory activity in the stratum oriens lamina of CA3, but for the kainate-induced oscillations, area power became significantly diminished in the stratum radiatum lamina of the GAD67-GFP (Deltaneo) mouse compared with the wild type mouse after prolonged exposure to kainate. This gradual reduction in area power in CA3 of the transgenic mouse was rescued by inclusion of Guvacine, a GABA uptake inhibitor, suggesting that the reported lower levels of GABA in the GAD67-GFP (Deltaneo) mouse brain during development and in the adult may contribute to a reduction in the efficiency of GABA neurotransmission after prolonged stimulation of the GABAergic circuitry.