Autonomous Purkinje cell activation instructs bidirectional motor learning through evoked dendritic calcium signaling

Optogenetically evoked Ca2+ signaling in PC dendrites. a Representative images from a single Pcp2::Cre;Ai27 mouse showing tdTomato-tagged ChR2 expression in the flocculus. In the magnified view, PCs are marked by calbindin immunostaining (molecular layer, ML; Purkinje cell layer, PCL; and granule cell layer, GCL). b The average fluorescence intensity profile of ChR2-tdTomato in the cerebellum of an example mouse. c ChR2-expressing PCs were filled with Fluo-5F during whole-cell recording. d Average Ca2+ transients from the same PC dendrite evoked by single pulses of light, shown relative to the climbing-fiber-evoked response. e Summary plot of peak Ca2+ transient amplitude for different stimulus conditions. f Simultaneous patch-clamp recordings from the soma and dendrite of ChR2-expressing PCs allowed for high-resolution measurement of optogenetically induced electrogenic activity. g Electrophysiological responses from the same PC to single pulses of light at increasing powers. h Plot shows the average number of optogenetically evoked dendritic spikes as a function of light power; the threshold for evoking reliable dendritic spiking is indicated by the dashed line.

The signals in cerebellar Purkinje cells sufficient to instruct motor learning have not been systematically determined. Therefore, we applied optogenetics in mice to autonomously excite Purkinje cells and measured the effect of this activity on plasticity induction and adaptive behavior. Ex vivo, excitation of channelrhodopsin-2-expressing Purkinje cells elicits dendritic Ca2+ transients with high-intensity stimuli initiating dendritic spiking that additionally contributes to the Ca2+ response. Channelrhodopsin-2-evoked Ca2+ transients potentiate co-active parallel fiber synapses; depression occurs when Ca2+ responses were enhanced by dendritic spiking. In vivo, optogenetic Purkinje cell activation drives an adaptive decrease in vestibulo-ocular reflex gain when vestibular stimuli are paired with relatively small-magnitude Purkinje cell Ca2+ responses. In contrast, pairing with large-magnitude Ca2+ responses increases vestibulo-ocular reflex gain. Optogenetically induced plasticity and motor adaptation are dependent on endocannabinoid signaling, indicating engagement of this pathway downstream of Purkinje cell Ca2+ elevation. Our results establish a causal relationship among Purkinje cell Ca2+ signal size, opposite-polarity plasticity induction, and bidirectional motor learning.

Bonnan, A., Rowan, M.M.J., Baker, C.A., Bolton, M.M., Christie, J.M. (2021). Autonomous Purkinje cell activation instructs bidirectional motor learning through evoked dendritic calcium signaling. Nature Communications 12, 2153.
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