mGluR1 Is a Molecular “Hub” for Synapse Elimination in the Developing Cerebellum

Functional neural circuits of mature animals are formed by elimination of redundant synapses and strengthening of necessary connections during postnatal development, a series of events termed synapse elimination. Postnatal development of climbing fiber to Purkinje cell synapses in the cerebellum is a representative model of synapse elimination. In neonatal rodents, Purkinje cells receive excitatory synaptic inputs from more than five climbing fibers with similar strengths. Until around postnatal day 17 (P17), a single climbing fiber is strengthened and redundant ones are eliminated in each Purkinje cell. The metabotropic glutamate receptor 1 (mGluR1) and its downstream molecules in Purkinje cells are essential for climbing fiber synapse elimination from around P14 to P17. Subsequent studies identified molecules that transmit elimination signal retrogradely from Purkinje cells to climbing fibers at the downstream of mGluR1. In this chapter, we make an overview of how mGluR1 and its downstream molecules regulate climbing fiber synapse elimination.