The Origin And Information Coding Properties Of Dual-peak Responses In Mouse Retinal Ganglion Cells

In vertebrate,retina is the first stage for visual information processing.Retinal ganglion cells(RGCs)are the output neurons where visual information is encoded in spikes and further transmitted to the central visual system.RGCs exhibit various activity patterns in response to visual stimuli,and can effectively encode visual information via many manners,such as firing rate,temporal structure of spike trains,and concerted activity,etc.In response to spatially uniform light flashes,RGCs show various light response characteristics: ON response,OFF response,ON-OFF response,and firing patterns: transient response,sustained response,etc.The different firing types are generated by different neural circuits in retina,and they employ different coding strategies.Besides,another response pattern exhibiting two peaks in peri-stimulus time histogram(PSTH)has also been reported,which is referred to as dual-peak response.Typically,this dual-peak response was composed of a transient component and another following component occurring shortly after the initial one.In this thesis,the firing activities of RGCs in mouse retina in response to full-field flashes were recorded by multi-electrode extracellular recording system,and the possible neural circuit generating the dual-peak response,and its coding strategies to transmit visual information were investigated.The main work includes three parts:(1)the main properties of dual-peak response;(2)the potential contribution of the inhibitory input mediated by GABAergic and/or glycinergic pathway(s)to the dual-peak response pattern;(3)the property changes(firing rate and response latency)of dual-peak response with different stimulus intervals,and the roles of different response characteristics in information coding.The main findings include:(1)The two peaks of the dual-peak responses exhibited distinct temporal dynamics.The first peak occurred rapidly at the stimulus onset with a relatively high firing rate and a short duration,exhibiting properties similar to those of the short-latency single-peak transient response.In contrast,the second peak could be either transient or sustained,with a longer latency and a lower peak firing rate,showing temporal properties similar to those of long-latency single-peak response.(2)Pharmacological studies demonstrated that when GABA or glycine was applied,the second response peak could be suppressed or even eliminated,while little change was induced in the first peak.Moreover,blockade of GABAergic or glycinergic pathway(s)did not block the dual-peak response,but induced the dual-peak responses in some transient cells by unmasking a second response phase.(3)Stimulus discrimination results demonstrated that both response peaks contributed to stimulus-duration coding,and better discrimination performance was obtained when the response parameters of both peaks were taken into account.In addition,RGC groups performed better in visual discrimination than single cells.In summary,our results showed that the two response peaks of the dual-peak response in mouse RGCs involve separate mechanisms,and arise from distinct pathways that converge on the ganglion cells,and they were both involved in retinal information coding,and might carry information complementary to each other.The particular pattern improves coding efficiency of RGCs.The investigation of response patterns of RGCs impoves our understanding of neural circuit and information coding in retina.And it also provides a meaningful indicator for understanding other neural systems.