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S. L. Mills, H. Hoshi; Two Distinct Types of ON Directionally-Selective Ganglion Cells in the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1870.
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It has long been known that there are two types of directionally-selective (DS) ganglion cells in the rabbit retina. ON-OFF DS ganglion cells project to the superior colliculus and lateral geniculate and are bistratified with processes that ramify in the cholinergic band. In contrast, ON DS ganglion cells project to the medial terminal nucleus and are reported to ramify in the ON cholinergic band only. Here we report that there are actually two distinctly different types of ON DS ganglion cells, both of which have been reported in the literature, but not previously distinguished.
Ganglion cells of the rabbit retina were visualized with acridine orange and recorded using the loose patch technique and subsequently stained by intracellular dye injection of Neurobiotin. Moving bars were presented using a Lucivid monitor mounted on the camera port and imaged through a 4X lens.
The two types of ON DS ganglion cells differ in several respects: (1) The branching patterns are discriminably different. (2) One type stratifies at the same depth as the dendrites of the ON cholinergic amacrine cells, while the other ramifies slightly more distal to the processes of the ON-OFF DS ganglion cell in the ON cholinergic band. (3) The more distal cell is extensively coupled to two types of amacrine cell and also to other ganglion cells of the same type. The other cell is never tracer-coupled. (4) The more distal cell responds about 75 ms following light onset, while the other is a sluggish cell, with latencies > 350 ms. (5) The more distal ganglion cell has a transient response; the other is sustained. (6) Nicotine only slightly increased spiking in the more distal ganglion cell, but dramatically increased spiking in the proximal cell, much like its effect on ON-OFF ganglion cells. However, the two types of cell are similar in sharing the same three cardinal axes of preferred motion and preference for slower motion than ON-OFF DS ganglion cells.
We found evidence for 2 separate types of ON DS ganglion cell. Examples of both types can be found in the previous literature. The ON DS ganglion cell recently studied by Ackert et al. (2006, 2009) appears to be the more distal, well-coupled type. Evidence from mouse also suggests the possibility of two distinct types of ganglion cells that project to MTN (Yonehara et al. 2009).
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