The Oscillations In The ON And OFF Pathways Of Bullfrog Retina

Vision is crucial for humans and other primates as the most important way to get information from the world.In the visual system,retina is the first stage for visual information processing.The output neurons of retina,retinal ganglion cells(RGCs),have various response patterns of spike trains which encode visual stimulation information.There is a special response pattern,the oscillation of RGC's activity,which has been observed in various species.It was reported that such oscillatory activity is involved in retinal information coding and may serve to perceptual integration.The oscillation is raised within neural network.However,the mechanism underlying oscillation is still unclear.In the present research,by studying the oscillatory activities in ON-OFF RGCs of bullfrog retina,we found that the mechanism underlying the oscillations in the ON pathway differs from that in the OFF pathways.The ON responses oscillated at higher frequencies than the OFF responses.Pharmacological experiments revealed that the oscillations in both ON and OFF pathways were abolished by GABA receptor antagonists,which indicates that GABAergic inhibition is essential for generating the oscillations in the two pathways.At the meantime,the oscillations in the ON and OFF pathways had different responses to several other applied drugs.The oscillation in the OFF pathway was abolished by glycine receptor antagonist or gap junction blocker,whereas the oscillation in the ON pathway was not affected.Furthermore,the blockade of the ON pathway by metabotropic glutamate receptor agonist led to suppression of the oscillation in the OFF pathway.These results suggest that the ON pathway has modulatory effect on the oscillation in the OFF pathway through an inhibitory cross circuit.This cross circuit is meditated by amacrine cell which is electrically coupled to ON bipolar cell and makes inhibitory glycinergic synapses onto OFF bipolar and ganglion cells.Therefore,the oscillation in the ON pathway is likely caused by GABAergic amacrine cell network,while the oscillation in the OFF pathway needs the contributions of both GABAergic amacrine cell network and glycinergic inhibition from the ON pathway.