Synaptic competition in central and peripheral nervous system: role of the postsynaptic cell

In central and peripheral nervous system the formation of a precise pattern of connections between neurons is the result of competitive synaptic processes occurring during development. In the embryonic stage neurons from redundant connetcions with a higher amount of target cells respect to those present in the adult. After birth supernumerary connections are lost after a process of peripheral refinement in which different inputs complete for the same target. Such process, called synaptic elimination, is generally accepted to be activity-dependent. The study of these competitive phenomena is considerably simplified in models in which at the end of the synaptic elimination the target cell is innervated by only one axon. These systems pass from a pattern of polyneuronal innervation to monoinnervation. In this PhD thesis two of these models are treated in different sections: the cerebellar cortex and the neuromuscolar junction. During development, in the cerebellar cortex various climbing fibers (CFs) innervate the perisomatic portion of a single Purkinje cell (PC). After a synaptic competition and elimination processes occurring mainly in the second postnatal week in mice and rats, each PC retains only one CF. In parallel climbing fibers terminations leaves the PC soma and are translocated in proximal dendritic compartment.