Abstract
Abstract: :
Purpose: To study the synchronized activity of neighboring ON direction selective (ON–DS) ganglion cells in the rabbit retina. Methods: Dual, simultaneous extracellular recordings were obtained from pairs of ON–DS cells visualized with transcleral infrared illumination in a flattened retinal preparation of the albino rabbit. Results: ON–DS ganglion cells were readily identified by their characteristic somatic labeling following application of the dye Azure B. We encountered ON–DS cells with preference for stimuli moving either along the vertical or horizontal axes. Interestingly, ON–DS cells within close proximity to one another were more likely to have the same preference for stimulus movement than more distant neighbors. Further, nearest neighbor DS cells were found to be tracer–coupled to a class of wide–field amacrine cell, thereby creating local clusters of coupled amacrine–ganglion cell networks. Neighboring DS cells showed synchronized spontaneous or light–evoked spike actvity with peak correlations at time zero in the cross correlogram functions. A remarkable finding was that whereas the average firing latency difference for pairs of neighboring ON–DS cells to stimuli moving in the preferred direction was 23 msec, the firing latency for stimulus movement in the non–preferred direction was significantly longer at 128 msec. Further, the firing latency differences to moving stimuli along non–preferred axes were in the 20–30 msec range, essentially equivalent to that seen for preferred movement. The latency difference for non–preferred stimulation was also seen as a lateral shift in the cross correlogram function of neighboring cells. Conclusions: Our findings suggest that ON–DS cells form circumscribed, electrical networks due to coupling via amacrine cells. This coupling underlies a default synchrony of the activity of neighboring cells. Preferred stimulus movement elicits an increased activity of ON–DS cells, which is synchronized with that of their neighbors. In contrast, non–preferred stimulus movement results not only in reduced spiking, but also a desynchronization of neighboring ON–DS cell activity. Thus, our results suggest that non–preferred stimulation results in not only reduced activity signaled to higher brain centers, but also increased latency differences and desynchronization of the responses of neighboring ON–DS cells. This could result in reduced efficacy of signals due to decreased temporal summation at central targets.
Keywords: ganglion cells • electrophysiology: non–clinical • retinal connections, networks, circuitry