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Voltage mapping of dendritic spikes in Purkinje neurons of awake mice

Christopher Roome

Okinawa Institute of Science and Technology (Japan)

14 Apr 2023 13:00

Aketxe Room, Sede Building, Leioa

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Dendritic spikes are thought to play an essential role in synaptic integration in vivo.

Dendrites may perform complex neuronal computations by modulating the propagation of dendritic spikes through specific dendritic processes. As such, ‘dendritic computational units’, could be determined by local synaptic inputs and encode specific synaptic input patterns. 

High resolution spatiotemporal voltage maps are necessary to investigate how dendritic spikes propagate in vivo. Using voltage imaging, we record dendritic voltage spikes in awake mice with high spatiotemporal resolution (Roome and Kuhn 2018). Single cerebellar Purkinje neurons were labelled with the voltage sensitive dye ANNINE-6plus and the genetically encoded calcium indicator GCaMP6f, using a chronic cranial window with access port (Roome and Kuhn, 2014), and imaged by two-photon microscopy (line scans at 2 kHz). 

In awake mice, we recorded rapid (1ms) dendritic spikes in the distal spiny dendritic branchlets. Dendritic complex spikes (DCS) typically comprising a ‘burst’ of 2-5 dendritic spikelets, were triggered by climbing fiber synaptic input and confirmed by their corresponding calcium signals. Climbing fiber synaptic inputs occurred spontaneously or were ‘evoked’ by sensory stimulation (air puff directed towards the eye).

To investigate how local synaptic inputs modulate dendritic spike propagation we used pharmacology, applied via micropipette, to selectively block excitatory and inhibitory metabotropic receptors (mGluR1 and GABAb respectively). These receptors are localized to Purkinje neuron spines and their interaction is expected to influence synaptic integration, by regulating synaptic plasticity.

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