Dissect The Regulate Mechanism Of Visual Signal Transmission Rapid Termination By Drosophila Visual Primary Neural Circuit

The visual nervous system is one of the most important sensory systems in an organism.Visual signal transmission has the characteristics of rapid beginning and rapid termination to maintain high temporal resolution.The termination depends on rapid deactivation of photorecetors and the downstream neurons.Previous studies reveal that photoresponse termination is controlled by the promptly deactivation of photoreceptors and the downstream visual signal transmission components and the negative feedback of horizontal cells and glial cells to photoreceptors.However,the underlying mechanism of the downstream neurons rapid deactivation remains less explored.In this dissertation,we use Drosophila as a model with a combinatorial approach of electroretinogram,genetics,immunohistochemistry and behavioral methods to dissect that how neural circuits regulate photoreceptors downstream neurons rapid deactivation.We find that disrupting the release of acetylcholine(ACh)in amacrine cells(ACs)results in slow ERG termination.ERG is an extracellular record that reflects light-induced mass response of the visual neurons.So we conducted intracellular recordings in photoreceptors and the downstream neurons to reveal that why disrupting transmission release of ACs results in slow ERG termination.We find that blocking synaptic ACh release have no effect on the repolarization process of photoreceptors,by contrast,the repolarization speed was significantly slower on the photoreceptors downstream L1/L2 neurons.When hyperpolarized L1/l2 neurons with inward rectifier potassium channel their ERG recordings show slow termination.Above of these,L1/L2 neurons repolarization is regulated by synaptic ACh release from ACs.We use GRASP technique to reveal the synaptic interaction between ACs and L1/L2 neurons,and reveal that L2 neurons receive ACh signal directly by acetylcholine receptors ?5,?7.In addition,we demonstrate that L4 neurons also regulate the repolarization of L1/L2 neurons with ACh signaling.Furthermore,when blocking the synaptic ACh release from both ACs and L4 neurons results in further slower ERG termination.This indicates that ACs and L4 neurons transmit ACh signal to speed up repolarization of L1/L2 neurons simultaneously.Finally,we reveal that blocking the release of ACh from ACs and L4 neurons,the ability of Drosophila to track moving objects significantly reduces upon high frequency light stimulation.Therefore,through electrophysiological and behavioral methods,we systematically analyze the mechanism and physiological effects of the rapid deactivation of the downstream neurons of photoreceptor cells.Our studies elucidate a novel mechanism of visual transmission rapid deactivation at the level of neural circuits.Our work will provide a new insight on sensory regulation and learning and memory.