Abstract
Nearby retinal ganglion cells of similar functional subtype have a tendency to discharge spikes in synchrony. The synchronized activity is involved in encoding some aspects of visual input. On the other hand, neurons always continuously adjust their activities in adaptation to some features of visual stimulation, including mean ambient light, contrast level, etc. Previous studies on adaptation were primarily focused on single neuronal activity, however, it is also intriguing to investigate the adaptation process in population neuronal activities. In the present study, by using multi-electrode recording system, we simultaneously recorded spike discharges from a group of dimming detectors (OFF-sustained type ganglion cells) in bullfrog retina. The changes in receptive field properties and synchronization strength during contrast adaptation were analyzed. It was found that, when perfused using normal Ringer's solution, single neuronal receptive field size was reduced during contrast adaptation, which was accompanied by weakening in synchronization strength between adjacent neurons' activities. When dopamine (1 µM) was applied, the adaptation-related receptive field area shrinkage and synchronization weakening were both eliminated. The activation of D1 receptor was involved in the adaptation-related modulation of synchronization and receptive field. Our results thus suggest that the size of single neuron's receptive field is positively related to the strength of its synchronized activity with its neighboring neurons, and the dopaminergic pathway is responsible for the modulation of receptive field property and synchronous activity of the ganglion cells during the adaptation process.
Highlights
Visual system operates under a wide range of light conditions with its limited range of firing response
In retinal ganglion cells (RGCs), adaptation to contrast has been well observed when the retina is exposed to sustained high contrast stimulus, in a sense that the onset of stimulus elicits high rate firing from the cell, and the firing rate is decreased progressively to a steady level which is much lower than its transient response [4,7]
Adaptive change of receptive field size The firing activity of a dimming detector in exposure to sustained pseudo-random checker-board flickering is plotted in Fig. 3A, which is similar to the previously reported contrastadaptation in retinal ganglion cells [4,7,28,29,30]
Summary
Visual system operates under a wide range of light conditions with its limited range of firing response. In this sense, adaptation can benefit the system encoding visual information under various visual environments for saving energy and improving signaling capability [1,2]. At the earliest stages of visual system, i.e., in the retina and the lateral geniculate nucleus (LGN), neurons adapt to some properties of input light including the mean light intensity and contrast [3,4,5,6]. Correlated activity between retinal ganglion cells induced by common inputs from presynaptic bipolar and amacrine cells is characterized by distributed time lags in the cross-correlogram between pair-wise neuronal firing sequences; while the precisely synchronized activity between the neighboring ganglion cells mediated by gap junctions is characterized by a sharp peak at zero-lag in the crosscorrelogram, in which case ganglion cells fire synchronously with a temporal precision of a couple of milliseconds
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