Title:
Postnatal refinement of the cerebellar climbing fiber to Purkinje cell synapse

Kouichi Hashimoto, Professor
Department of Neurophysiology, Graduate School of Biomedical Sciences,
Hiroshima University

Abstract:
Neuronal circuits are initially redundant in neonatal animals, but rearranged during postnatal development in the activity dependent manner. In the adult cerebellar system, each Purkinje cell (PC) is innervated by a single strong climbing fiber (CF) originating from the inferior olive in the medulla oblongata. In contrast, PCs are innervated by multiple weak CFs at birth. Surplus CFs are eliminated by the end of the third postnatal week in mice or rats. Recent analyses have demonstrated that the postnatal refinement of CFs is mediated by several developmental phases. During the first postnatal week, single CFs are strengthened relative to other ones on individual PC somata (functional differentiation). Then, only the strengthened CFs selectively translocate to dendrites after P9 (CF translocation), while terminals of other weaker CFs are remained on the PC soma. Massive elimination of the weaker CFs on PC somata occurs in two distinct elimination processes (the early- and the late-phase of CF elimination processes). In this seminar, I would like to discuss molecular mechanisms underlying these developmental stages.

References:
1. Hashimoto, K. et al. Postsynaptic P/Q-type Ca 2+ channel in Purkinje cell mediates synaptic competition and elimination in developing cerebellum. Proc Natl Acad Sci U S A 108, 9987-92 (2011).

2. Hashimoto, K., Ichikawa, R., Kitamura, K., Watanabe, M. & Kano, M. Translocation of a “winner” climbing fiber to the Purkinje cell dendrite and subsequent elimination of “losers” from the soma in developing cerebellum. Neuron 63, 106-18 (2009).

3. Hashimoto, K. & Kano, M. Functional differentiation of multiple climbing fiber inputs during synapse elimination in the developing cerebellum. Neuron 38, 785-96 (2003).