Spike timing-dependent selective strengthening of single climbing fibre inputs to Purkinje cells during cerebellar development.

Shaping functional neural circuits in developing brain involves activity-dependent refinement of early-formed redundant synapses. In the developing cerebellum, a one-to-one connection between a climbing fibre (CF) and a Purkinje cell (PC) is established by selective strengthening of a single CF followed by elimination of surplus CFs. Here we investigate developmental changes in CF-mediated responses in PCs by using in vivo whole-cell recordings and two-photon Ca(2+) imaging. We show that each neonatal PC receives temporally clustered inputs from multiple CFs and temporal integration of these inputs is required to induce burst spiking and Ca(2+) rise in PCs. Importantly, a single CF input closest to PC's spike output is selectively strengthened during postnatal development. This spike timing-dependent selective strengthening is much less prominent in PC-selective P/Q-type voltage-dependent Ca(2+) channel knockout mice. Thus, spike timing- and Ca(2+)-dependent plasticity appears to underlie the selection of a single 'winner' CF and the establishment of mature CF-PC connections.