The Modulation Of Dopaminergic Pathway On Population Activities In Bullfrog Retinal Ganglion Cells

The retina is the first stage for visual information processing.Photoreceptors convert the light stimulus into electrical signals which arefurther processed by retinal circuits. Retinal ganglion cells, the outputneurons of retina, send all the visual information to the brain using spikestransmitted through their axons. Nearby retinal ganglion cells of similarfunctional subtype have a tendency to discharge spikes in synchrony. Thesynchronized activity is involved in encoding some aspects of visualinput. On the other hand, neurons always continuously adjust theiractivities in adaptation to some features of visual stimulus, includingmean ambient light, contrast level, etc. The present work is mainly aimedto investigate the dynamic modulation and efficient aspects ofinformation processing in the retina, employing electrophysiological andtheoretical approaches. The main work includes three parts:(1)investigating the adaptation-dependent changes of synchronous activityand receptive field;(2) dopaminergic modulation underlying synchronousactivity and receptive field changes;(3) comparison of dopaminergic modulation underlying synchronous activity and correlated activity;(4)the performance of ganglion cells in pattern discrimination and the effectsof dopamine on pattern discrimination.The main findings including:(1) single neuronal receptive field sizewas reduced during contrast adaptation, which was accompanied byweakening in synchronization strength between adjacent neurons’activities;(2) during dopamine application, the synchronization strengthand receptive field area were significantly increased. Theadaptation-related receptive field area shrinkage and synchronizationweakening were both eliminated. The activation of D1receptor wasinvolved in the adaptation-related modulation of synchronization andreceptive field;(3) dopaminergic pathway exerted different effects onsynchronized activity and correlated activity;(4) ganglion cell populationactivities exhibited distinct response features in exposure to variousstimulation patterns and exhibited higher correct rate in stimulusdiscrimination as compared with single cell’s activity. Dopamineapplication did not significantly change the performance of single neuronactivity, but increased the synchronization strength of the ganglion cells’activities and decreased the correct rate of stimulation patternsdiscrimination.These results clearly indicated that the size of single neuron’sreceptive field is positively related to the strength of its synchronized activity with its neighboring neurons, and the dopaminergic pathway isresponsible for the modulation of receptive field property andsynchronous activity of the ganglion cells during the adaptation process.Retinal ganglion cells discriminate various stimulation patterns viasynchronous activities among population neurons, and DA-inducedincrease in synchronous activities weaken the population performance inpattern discrimination, indicating the potential role of dopaminergicpathway in the modulation of population coding process.