ANTINOMIC LOCALIZED YET BROAD DENDRITIC COMPUTATION IN PURKINJE CELL DENDRITE REVEALED BY VOLTAGE IMAGING

Neurons receive numbers of synaptic inputs in their elaborate dendrite. How individual synaptic potentials travel through somatodendritic compartment and how they are integrated are central to neuronal computation. However, the spatial processing of voltage signals remains obscure, mainly because of the difficulty of simultaneous patch-clamp recordings from multiple points in a complex branching dendrite. Here, we expressed a genetically-encoded voltage indicator in cultured cerebellar Purkinje cells (PCs) and conducted voltage imaging of EPSPs evoked by spot laser uncaging of MNI-glutamate. EPSPs generated at a distal branch sharply attenuated in short distance (length constant ~ 30 micrometers) and surprisingly similar, substantial size of voltage changes were shared in the remaining wide dendritic area. Multi-compartmental model simulation revealed that the characteristic branching pattern of PC dendrite was the determinant factor for the EPSPs spreading pattern. We further examined the integration of EPSPs in PC dendrite using voltage and calcium imaging. EPSPs in response to simultaneous glutamate uncagings at two faraway branches showed spatial spreading pattern similar to the superimposed pattern of two individual ones. Increasing uncaging intensity and numbers triggered calcium spikes. The area of calcium rise was limited close to the area near the stimulated site, specified by the length constant for voltage signal attenuation. On the other hand, paired uncagings on a faraway branch decreased the stimulus intensity needed to evoke calcium spikes on a branch, highlighting inter-branch summation of synaptic inputs enabled by widespread voltage signals.