Taken together, AMPA receptors expressed in Purkinje cells are considered to be GluA1/GluA2 or GluA2/GluA3 heteromeric channels. In contrast, AMPA receptors lacking GluA2, such as GluA1/GluA3 heteromeric channels and GluA1 or GluA3 homomeric channels, are little expressed, if at all, in Purkinje cells. Notably, AMPA receptors remaining in γ-2-KO, γ-7-KO and DKO Purkinje cells all preserved the linear I-V relationship, even although GluA2 expression was significantly reduced in Purkinje cells of these KO mice. From these findings, it can be assumed that in Purkinje cells the ablation of γ-2 causes severe reduction in GluA2/GluA3 channels,

which results in severe reduction in AMPA receptor-mediated currents. The remaining GluA1/GluA2 channels probably mediate residual currents in γ-2-KO Purkinje cells. This large current deficit in γ-2-KO Purkinje

cells suggests that GluA2/GluA3 channels Selleckchem CDK inhibitor are the predominant channel in Purkinje cells. This possibility appears to be supported by consistently much lower density Target Selective Inhibitor Library of immunogold labeling for GluA1 than for GluA2 and GluA3 at the climbing fiber–Purkinje cell synapse (M. Fukaya, M. Yamasaki and M. Watanabe, unpublished observation). The large deficit may also reflect tonic enhancement of AMPA receptor channel function by γ-2 (Yamazaki et al., 2004; Kato et al., 2007, 2008). In contrast, similar levels of GluA1–GluA3 localization and AMPA receptor-mediated currents at γ-7-KO climbing fiber–Purkinje pheromone cell synapses suggest normal synaptic expression of GluA2/GluA3 and GluA1/GluA2 channels. By the ablation of both TARPs, however, GluA2/GluA3 channels are depleted almost completely and GluA1/GluA2 channels are also reduced substantially, leading to more severe deficits at all the biochemical, electrophysiological

and behavioral levels. In future studies, it would be intriguing to pursue whether such a subunit-dependent regulation by multiple TARPs plays a role in activity-dependent insertion, internalization and recycling of GluA1/GluA2 and GluA2/GluA3 channels. These are considered to be key mechanisms underlying the changes in synaptic strength observed during several forms of long-term potentiation and long-term depression (Shi et al., 2001; Malinow & Malenka, 2002; Song & Huganir, 2002; Lee et al., 2004). The synergistic promotion of synaptic GluA2–GluA4 expression by γ-2 and γ-7 was demonstrated reproducibly by Western blot, light microscopic immunohistochemistry and postembedding immunogold electron microscopy. By contrast, the lack of apparent reductions in synaptic localization of GluA1 and GluA4 in γ-7-KO mice (except for GluA4 at the mossy fiber–granule cell synapse) was inconsistent with their substantial reductions in cerebellar contents and immunohistochemical signals in the molecular layer. This discrepancy was explained by substaintal loss of GluA1 and GluA4 in Bergmann glia.