Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Fast Vesicle Reloading Sustains High Bandwidth

 

Nature 439, 983-987(23 February 2006) | doi:10.1038/nature04509; Received 6 October 2005; Accepted 25 November 2005

Fast vesicle reloading and a large pool sustain high bandwidth transmission at a central synapse

Chiara Saviane and R. Angus Silver

Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK

(paraphrase)

What limits the rate at which sensory information can be transmitted across synaptic connections in the brain? High-frequency signalling is restricted to brief bursts at many central excitatory synapses, whereas graded ribbon-type synapses can sustain release and transmit information at high rates. Here we investigate transmission at the cerebellar mossy fibre terminal, which can fire at over 200 Hz for sustained periods in vivo, yet makes few synaptic contacts onto individual granule cells. We show that connections between mossy fibres and granule cells can sustain high-frequency signalling at physiological temperature. We use fluctuation analysis and pharmacological block of desensitization to identify the quantal determinants of short-term plasticity and combine these with a short-term plasticity model and cumulative excitatory postsynaptic current analysis to quantify the determinants of sustained high-frequency transmission. We show that release is maintained at each release site by rapid reloading of release-ready vesicles from an unusually large releasable pool of vesicles (~300 per site). Our results establish that sustained vesicular release at high rates is not restricted to graded ribbon-type synapses and that mossy fibres are well suited for transmitting broad-bandwidth rate-coded information to the input layer of the cerebellar cortex.

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