Summary
Sensory circuits adapt to changes in the external world or the animal’s internal state through the actions of neuromodulators1,2. Synapses are key sites at which neuromodulators act3,4 but it is not known how they alter the amount of information transmitted5. We investigated this question in the context of the diurnal regulation of visual processing in larval zebrafish, focusing on ribbon-type synapses of retinal bipolar cells6. 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”, reduced variability of stimulus-evoked release and improved temporal precision. Simultaneously, an increase in the probability of multivesicular events with larger information content increases the efficiency of information transmission (bits per vesicle) by factors of 2-3. The neuromodulator dopamine contributes to all these changes in synaptic function, although ON and OFF visual channels are differentially affected. Multivesicular release is a property of synapses in many parts of the brain7-11 and this study demonstrates that it’s potentiation by neuromodulators can both increase the amount of information that is transmitted and the efficiency of transmission, revealing a previously unknown mechanism for adjusting neural processing.
Competing Interest Statement
The authors have declared no competing interest.
