Differences Of Neuronal Network Between ON And OFF Pathways In Bullfrog Retina

Visual system consists of two separate pathways–ON-andOFF-pathway, and the segregation of these two pathways originates frombipolar cells in retinas. ON pathway prefers to signal light increment andOFF pathway prefers to light decrement. ON-and OFF-pathway havedifferent temporal and spatial characteristics, including responsesensitivity, temporal kinetics, receptive field size and concerted activity.These differences may due to different neuronal properties and neuralnetwork wiring in ON-and OFF-pathway. The present work is mainlyaimed to investigate the differences of neuronal network between ON andOFF pathways in bullfrog retina. The main work includes two parts:(1)investigating the differences of type and strength of concerted activitybetween ON responses and OFF responses of bullfrog retinal ON-OFFganglion cells;(2) the influence of GABAergic inhibition on the strengthof concerted firing of ON-/OFF-responses and their differences.The main findings were:(1) ON responses often exhibited correlatedactivity, whereas OFF responses often exhibited synchronized activity;(2) There was no appreciable difference between the strength ofsynchronized activity between ON and OFF responses;(3) The strengthof correlated activity of ON responses was significantly greater than thatof OFF responses;(4) GABAA-receptor-mediated inhibitory pathwayssignificantly reduced the synchronized strength of ON-/OFF-responsesand significantly increased the correlated strength of ON-/OFF-responses;(5) GABAA-/GABAC-receptor-mediated inhibitory pathways had nosignificant influence on the difference between the synchronized strengthof ON-responses and OFF-responses;(6) GABAA-receptor-mediatedinhibitory pathways reduced the difference between the correlatedstrength of ON-responses and OFF-responses, whileGABAC-receptor-mediated inhibitory pathways increased the differencebetween the correlated strength of ON-responses and OFF-responses.The results suggest that correlated activity induced by commoninputs mainly exists in ON pathway, while synchronized activitymediated by gap junction exists in both ON and OFF pathway.Furthermore, GABAA/GABAC-receptor-mediated inhibitory pathwayshave different influence in regulating the correlated strength ofON-responses and OFF-responses. GABAergic inhibitory pathways don’tsimply and passively inhibit neuronal activity, but maybe activelyparticipate in the information processing and functional organization inthe retina.