The profile of EEG power of Kif5a-conditional KO mice showed a significant power reduction in both rest and locomotive states, suggesting that neuronal network activity is impaired by postnatal loss of KIF5A. All procedures were approved by the Graduate School of Medicine, The University of Tokyo. Because it is known that disturbance of inhibitory synaptic transmission is involved in epileptic seizure generation (Jacob et al., 2008; Rudolph and Möhler, 2004), we speculated that GABAergic synaptic transmission may be impaired in the hippocampus of Kif5a-conditional

KO mice. We performed Adriamycin whole-cell patch-clamp recordings to investigate the miniature Screening Library cell assay inhibitory postsynaptic currents (mIPSCs) in the CA1 region of hippocampal

slices ( Figure 2A). We observed a significantly reduced mean amplitude of mIPSCs in the slices of Kif5a-conditional KO mice compared with those of controls (control, 16.5 ± 0.7 pA; conditional KO, 8.5 ± 0.4 pA). A cumulative probability curve also indicated a leftward shift to smaller amplitudes in Kif5a-conditional KO mice ( Figure 2F). However, the frequency, rise time, and decay time, although slightly reduced, were not statistically different between genotypes ( Figures 2C–2E and 2G). Furthermore, the ratio of evoked (e)IPSC (upward traces in  Figure 2H) to 2-amino-3-(5-methyl-3-oxo-1, 2-oxazol-4-yl) propanoic acid (AMPA)-mediated evoked EPSC (downward traces in Figure 2H) was reduced in Kif5a-conditional KO mouse slices, compared with that in control mafosfamide mouse slices ( Figure 2H), showing a relative reduction in eIPSC amplitudes in Kif5a-KO neurons. Taken together, these results suggest that GABAA receptor (GABAAR)-mediated synaptic transmission is impaired in the hippocampus of Kif5a-conditional KO mice. Next, to investigate network excitability, we measured

stimulus-evoked population spikes in hippocampal slices of Kif5a-conditional KO and control slices. Epileptiform activities were more frequently observed in Kif5a-conditional KO slices in both standard and Mg2+-depleted artificial cerebrospinal fluid (ACSF), indicating increased excitability in these tissues ( Figures 2J–2O). To investigate the cause of impairment in inhibitory synaptic transmission, we compared cell surface expression of GABAARs in primary hippocampal neurons derived from Kif5a-KO and WT embryos. Most GABAARs at synapses are thought to be composed of two α1, α2, or α3 subunits together with two β2 or β3 subunits and a single γ2 subunit. Using the surface biotinylation method, the cell surface expression level of GABAARβ2 was assessed. In KO neurons, cell surface expression of GABAARβ2 was significantly reduced (52.6% ± 4.9% versus WT), whereas that of GluR2/3 was unchanged ( Figures 3A and 3B).