Activity-dependent maturation of climbing fiber to Purkinje cell synapses during postnatal cerebellar development.

Cerebellar Purkinje cells (PCs) of newborn rodents are innervated by multiple climbing fibers (CFs). During the first postnatal week, single CFs are strengthened relative to other CFs on the somata of individual PCs. Then, the strengthened CFs undergo translocation to PC dendrites after P9. Elimination of the weaker CFs occurs in two distinct steps, namely the early phase from P7 to around P12 and the late phase from about P12 to around P17. Our previous study demonstrates that CF synapse elimination is severely impaired in null mutant mice lacking Ca(v)2.1, a pore-forming component of P/Q-type voltage-dependent Ca(2+) channel (VDCC). To examine the contribution of postsynaptic P/Q-type VDCC to postnatal rearrangement of CFs, we generated mice with PC-selective deletion of Ca(v)2.1 (PC-Ca(v)2.1 KO). We made whole-cell recordings from PCs in cerebellar slices and examined CF-mediated excitatory postsynaptic currents. We found that PC-Ca(v)2.1 KO PCs had severe defects in selective strengthening of single CFs during the first postnatal week and subsequent CF synapse elimination from P7. Moreover, our morphological analysis revealed that multiple CFs abnormally underwent translocation to PC dendrites in PC-Ca(v)2.1 KO mice. These results indicate that Ca(2+) influx through P/Q-type VDCC into PCs is crucial for selective strengthening of single CFs, early phase elimination and selective translocation of single strengthened CFs to PC dendrites.