Gap Junction Permeability Modulated By Dopamine Exerts Effects On Spatial And Temporal Correlation Of Retinal Ganglion Cells’ Firing Activities

The retina is the first stage for visual information processing. Thelight stimulus is converted into electrical signals by photoreceptors and theelectrical signals are further processed by neural circuits. After processedby retinal ganglion cells, all the visual information is encoded and sent tothe brain in the form of spikes. Neighboring retinal ganglion cells ofsimilar subtype tend to release spikes in synchrony, which is the spatialcorrelation between adjacent neurons. This correlated activity is involvedin encoding some aspects of visual information. The synchronized activity,one of the correlated activity subtypes, mediated by gap jucntions betweenretinal ganglion cells can be enhanced by dopamine. In addition to thespatial correlation, the action potentials within single neuron’s spike trainare correlated with each other, which is the temporal correlation withinspike trains. These two kinds of correlations are highly positivelycorrelated. Considering the effects of dopamine on the synchronizedactivity, one intriguing question is how the enhanced spatialsynchronization alters the temporal firing structure of single neurons. Thisdissertation studies the dopamine’s regulation on the spatial-temporalcorrelated firing activities of retinal ganglion cells in bullfrog’s retina andthe potential role of dopaminergic pathway in in this modulation.The main contents include two parts:(1) temporal structures of singleneurons’ spike trains before and after the application of dopamine werestudied with plot of previous versus subsequent inter-spike-intervals;temporal correlation of single neurons’ spike trains was measured based on information theory. Data analysis results showed that, during application ofdopamine, synchronized activities between single neuron and itsneighboring neurons were enhanced, and in the meantime, the temporalstructures of single neuron spike train changed significantly (the number ofsmall inter-spike-intervals (<6ms) reduced and that of largeinter-spike-intervals (>10ms) increased), and the temporal correlation insingle neuron’s response decreased;(2) further investigation withapplication of dopamine receptor antagonists suggested that the dynamicchanges in firing patterns might be mainly caused by the activation of D1receptors.These results indicated that exogenous dopamine up-regulated the gapjunctional permeability which enhanced the synchronization of dimmingdetectors’ firing activities. In the meantime, the temporal structures ofsingle neuron spike train changed significantly, and the temporalcorrelation in single neuron’s response decreased. The increase of spatialcorrelation may indicate that the transmission of encoded visualinformation became more effective, but some information details will belost. In the meantime, some information features and transformationefficiency would be lost during encoding the visual scenes due to thedecrease of temporal correlation. Our results suggested that thedopaminergic pathway participated in the modulation of spatial andtemporal correlation of retinal ganglion cells’ firing activities, and mightexert critical effects on visual information processing in the retina. Inconsideration of the DA’s daily rhythm of its release, the retina may chosedifferent encoding strategy for input visual stimulus based on variousenvironments.