Diurnal modulation of multivesicular release controls the efficiency of information transmission at a sensory synapse

Abstract

SummaryNeuromodulators adjust sensory circuits to changes in the external world or the animal’s internal state and synapses are key control sites for such plasticity. Less clear is how neuromodulation alters the amount of information transmitted through the circuit. We investigated this question in the context of the diurnal regulation of visual processing in zebrafish, focusing on synapses of retinal bipolar cells. We demonstrate that contrast-sensitivity peaks in the afternoon accompanied by an average four-fold increase in the Shannon information transmitted at individual active zones. This increase reflects higher synaptic gain, lower spontaneous “ noise” and reduced variability of evoked responses. Simultaneously, an increase in the probability of multivesicular events with larger information content increases the efficiency of transmission (bits per vesicle) by factors of 2-3. This study demonstrates how the potentiation of multivesicular release by neuromodulators can increase the synaptic transfer of information and the efficiency of the vesicle code.