52 ± 0.16, n = 9; GAD67+/GFP: 3.74 ± 0.52, n = 18; p = 0.017) (Figures 8B and 8C). While somatic Ca2+ transients elicited by CF-multi-W was significantly smaller than those by CF-multi-S in control mice (CF-multi-W: Y-27632 ic50 1.52 ± 0.16, n = 9; CF-multi-S: 4.15 ± 0.48, n = 13; p = 0.002) (Figures 8B and 8C), there was no significant difference in Ca2+ transients between CF-multi-W and CF-multi-S in GAD67+/GFP mice (CF-multi-W: 3.74 ± 0.52, n = 18; CF-multi-S: 5.59 ± 0.90, n = 16; p = 0.255) (Figures 8B and 8C). These results indicate that, in GAD67+/GFP mice, CF-multi-W can elicit Ca2+ transients in the PC soma comparable to those induced by CF-multi-S. In

contrast to CF-multi-W, stimulation of CF-multi-S induced large Ca2+ transients in PC dendrites, but the magnitudes were not different between control and GAD67+/GFP mice (control: 16.8 ± 2.48, n = 12; GAD67+/GFP: 19.6 ± 6.30, n = 14; p = 0.487) (Figures 8B and 8D). Importantly, bath click here application of diazepam (1 μM) significantly reduced the somatic Ca2+ transients by CF-multi-W in GAD67+/GFP mice (n = 8, p = 0.014) (Figure 8E) to the same level as those in control mice without diazepam (GAD67+/GFP with diazepam: 2.18 ± 0.39, n = 8; control without diazepam: 1.52 ± 0.16, n = 9; p = 0.127). Thus, diazepam eliminated the difference in the magnitude of somatic Ca2+ transients by CF-multi-W between the two mouse strains, which

is considered to be a major cause of the diazepam-induced rescue of the impaired CF synapse elimination in GAD67+/GFP mice (Figure 5). These results indicate that diminished inhibition to the PC soma permits CF-multi-W to induce much larger somatic Ca2+ transients in GAD67+/GFP mice than in control mice. The somatic Ca2+ transients in GAD67+/GFP mice might be large enough to counteract developmental synapse elimination that otherwise prunes CF-multi-W during the second first postnatal week (Hashimoto et al.,

2009a). Since Ca2+ signals induced by direct depolarization of PCs were almost abolished by the P/Q-type VDCC blocker in both strains of mice (Figure S3U), it is highly likely that Ca2+ transients by activating CF-multi-W or CF-multi-S are mediated mostly by P/Q-type VDCC. Thus, control of P/Q-type VDCC activity and resultant Ca2+ transients by GABAergic inhibition appears to be crucial for CF synapse elimination from P10 to P16. Besides the well-established role as a major inhibitory transmitter in the mature brain, GABA has been implicated in multiple aspects of neural development (Owens and Kriegstein, 2002). Here, we have demonstrated that GABA, as an inhibitory transmitter, regulates developmental synapse elimination in the cerebellum. In GAD67+/GFP mice, GABAergic transmission onto PCs was attenuated during the second postnatal week and CF synapse elimination was impaired after P10.