J Neurophysiol (May 1, 2003). 10.1152/jn.00884.2002
Submitted on Submitted 3 October 2002; accepted in final form 28 January 2003

Sodium Imaging of Climbing Fiber Innervation Fields in Developing Mouse Purkinje Cells

 ¹Laboratory for Neuronal Circuit Dynamics, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako-Shi, Saitama 351-0198, Japan; and  ²Department of Neuroscience and Rita Montalcini Centre for Brain Repair, University of Turin, I-10125 Turin, Italy

Scelfo, Bibiana, Piergiorgio Strata, and Thomas Knöpfel. Sodium Imaging of Climbing Fiber Innervation Fields in Developing Mouse Purkinje Cells. J. Neurophysiol. 89: 2555-2563, 2003. Maturation of specific neuronal connections in the mature nervous system includes elimination of redundant synapses formed earlier during development. In the cerebellum of adult animals, each Purkinje cell (PC) is innervated by a single climbing fiber (CF). In early postnatal development each PC is innervated by multiple CFs and elimination of synapses formed by supernumerary CFs occurs until monoinnervation is established at around postnatal day 20 (P20) in mice. It is not clear whether multiple CFs, or only a single CF, translocate from the cell body of immature PCs to the developing dendrite and, in case several CFs translocate, whether they share or segregate their innervation fields. To localize CF innervation fields, we imaged changes in postsynaptic sodium concentration resulting from CF-mediated postsynaptic currents. We found that more than one CF translocates from an innervation field on the cell body of the PC to the developing dendrite and that these CFs share rather than segregate their innervation fields. We concluded that both the soma and the proximal dendrite of the PC are territories of competition for the developing CFs and that the overlapping of their termination fields may be the prerequisite for a local process of elimination of all but one CF, as previously demonstrated in the developing neuromuscular junction.