Abstract
AbstractThe architecture of parallel fiber (PF) axons contacting cerebellar Purkinje neurons (PNs) retains spatial information over long distances. PF synapses can trigger local dendritic calcium spikes, but whether and how this calcium signal leads to plastic changes that decode the PF input organization is unknown. By combining voltage and calcium imaging, we show that PF-elicited calcium signals, mediated by voltage-gated calcium channels, increase non-linearly during high-frequency bursts of electrically constant calcium spikes because they locally and transiently saturate the endogenous buffer. We demonstrate that these non-linear calcium signals, independently of NMDA or metabotropic glutamate receptor activation, can induce PF long-term potentiation (LTP). Two-photon imaging in coronal slices revealed that calcium signals inducing LTP can be observed by stimulating either the PF or the ascending fiber pathway. We propose that local dendritic calcium spikes, evoked by synaptic potentials, provide a unique mechanism to spatially decode PF signals into cerebellar circuitry changes.
Highlights
In this report we show that parallel fiber (PF)-elicited dendritic calcium spikes can induce postsynaptic PF-long-term potentiation (LTP) in the mouse cerebellum
Since dendritic excitation depends on the spatiotemporal summation of synaptic inputs, the present results suggest that a major physiological role of PFevoked dendritic calcium spikes is to functionally associate cerebellar granule cell axons synchronously targeting the same Purkinje neurons (PNs) dendritic region
Dendritic calcium spikes and non-linear summation of calcium signals elicited by PF-EPSPs
Summary
CF-mediated Δ[Ca2+]i signals are small, when paired with a short delay after PF-EPSPs bursts, CF-EPSPs are associated with a supra-linear dendritic Δ[Ca2+]i signal, independent of the activation of mGluR1s and calcium release from stores [12]. In the region of PF-evoked dendritic calcium spikes, the Δ[Ca2+]i signal associated with the CF-EPSP increased during the pairing protocol (Fig. 3d).
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