POSTPONED - NEW DATE TBC

A Circuit Neuroscience Seminar (CNS)

Neuromodulators adjust sensory processing and synapses are key control sites for such plasticity. Less clear is how neuromodulation alters the amount of information that synapses transmit through a circuit. To understand the  operation of the “vesicle code” the experimenter needs to isolate signals from individual active zones with a resolution of single vesicles while observing or controlling the incoming signal. This has not been possible using  electrophysiology but can now be achieved by multiphoton imaging of the glutamate reporter iGluSnFR in the retina of larval zebrafish. Here we investigate the visual signal as it is transmitted through the synapses of bipolar cells  (BCs). These synapses represent an information bottleneck in vision because they are the only route for transmission of signals originating from photoreceptors. This approach reveals that the visual message transmitted from BCs does not use a simple binary code but is instead composed of a number of symbols, composed of one, two, three or more vesicles released as one event. Here we demonstrate that this strategy of coding by amplitude as well as rate is under diurnal control, contributing to a four-fold variation in the Shannon information transmitted at individual active zones. Dopamine contributes to this increase in information transfer by adjusting at least four synaptic properties; the number of vesicles released by a stimulus, spontaneous synaptic noise, the variability of stimulus-driven responses and the balance between univesicular and multivesicular release. By increasing the probability of multivesicular events with larger information content, dopamine also increases the efficiency of transmission quantified as bits per vesicle. These results provide a quantitative understanding of the different mechanisms by which neuromodulators alter the flow of sensory information.

 

Thanks to some generous support from the British Neuroscience Association we will be able to have a chat with the speaker over food and refreshments after the talk, details to follow.