Field Potentials in the Fly’s Photoreceptor-LMC Synapse: A Possible Mechanism for Regularizing Vesicle Release

The first synapse in the fly visual system, from photoreceptor to Large Monopolar Cell (LMC), is capable of transmitting information at high rates. The primary physiological mechanism for signal transmission in this system involves the release of synaptic vesicles, leading to graded postsynaptic voltage changes. Previous studies have suggested that measured information rates are difficult to explain on the assumption that the photoreceptor terminal releases vesicles according to Poisson statistics (de Ruyter van Steveninck and Laughlin, Nature 379: 642-645 (1996)). Work by Weckström and Laughlin (J Neurosci 30(28): 9557-9566 (2010)) has demonstrated that the LMC postsynaptic currents generate substantial extracellular potentials in the extracellular space. Here I will explore the possibility that these field potentials play a role in regularizing the statistics of vesicle release, enabling the synapse to transmit information at high rates while maintaining a modest average vesicle release rate.