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A novel sorting mechanism of synaptic currents in the cerebellar Purkinje cell dendrites
― Dendritic excitability plasticity determines the conduction of synaptic current on cerebellar Purkinje cells ―
Gen Ohtsuki
The Hakubi Center for Advanced Research, Kyoto University
Department of Biophysics, Kyoto University Graduate School of Science

In this study, I found that whether the conduction of postsynaptic current to the cell body is regulated by the different excitability of the individual dendrites in the Purkinje cells, which are the main output neurons of the cerebellum. Furthermore, I found that the mechanism of excitability change, which is called intrinsic plasticity, facilitated conduction of post-synaptic currents via a reduction of potassium-channel activity. This phenomenon is caused from the membrane properties of the dendrites and is a new type of plasticity that is different from synaptic plasticity.
First, I confirmed that synaptic input to the distal dendrite is not efficiently conducted to the cell body by recording the postsynaptic current simultaneously from Purkinje cell body and dendrite, in the slice preparation of the rat cerebellum. On the other hand, under conditions where excitability plasticity was induced or the activity of SK channels, a type of calcium-activated potassium channels, was suppressed, postsynaptic current was efficiently conducted to the cell body. Furthermore, by calculating the ratios of simultaneously recorded post-synaptic currents, it was also possible to estimate that Purkinje cells have an average of 4.5 cluster inputs (Figure). Surprisingly, the number of cluster inputs was reduced by both of excitability plasticity and suppression of SK channels, meaning that the selection of synaptic input for each dendrite has been disrupted by global induction of excitability plasticity. These results suggest a new type of regulatory mechanisms for the selection of synaptic transmission; however, the implications for cerebellar learning should be investigated further.

Modification of Synaptic-Input Clustering by Intrinsic Excitability Plasticity on Cerebellar Purkinje Cell Dendrites.
Ohtsuki G. Journal of Neuroscience, 2019, 3211-18. (Early publication on 21 November 2019). corresponding author. Single-authored.
DOI: https://doi.org/10.1523/JNEUROSCI.3211-18.2019

<Figure Legends>
Figure Title: Cerebellar Purkinje cells conduct post-synaptic currents differently for each dendrite.
Figure shows a schematic diagram of currents recorded with two fine glass electrodes from a Purkinje cell body and dendrite. The red electrode is from dendrite and the black electrode is from the cell body. The color of the current trace is matched.
Excitatory post-synaptic currents recorded simultaneously from a Purkinje cell do not match in magnitude between dendrite and cell body. In addition, group data of the ratios of excitatory postsynaptic current amplitudes showed multiple subgroups with similar ratio values (colored dots over traces), suggesting that synaptic inputs are clustered in Purkinje cells.

The Hakubi Center for Advanced Research, Kyoto University, Japan
Department of Biophysics, Kyoto University Graduate School of Science, Japan