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C. S. Cowan, S. M. Wu; Relative Strengths of Rod and Cone Inputs to Multiple Simultaneously Recorded Ganglion Cells in the Salamander Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1871.
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© ARVO (1962-2015); The Authors (2016-present)
To identify the relative strengths of rod and cone inputs to physiologically identified ganglion cell classes in the salamander retina. Multielectrode recording techniques are used to provide a control for light adaptation that was not available in past serial approaches.
Dark adapted salamander retinas were perfused in oxygenated Ringer’s and placed in a recording chamber with ganglion cells facing an electrode array. Whole field light flashes of 1s duration were presented. Light wavelength was varied between trials by bandpass filtering at 500nm or 700nm and light intensity was varied across 7 log units. Salamander cones display similar intensity-response profiles to 500nm and 700nm light while rods show a marked preference for 500nm light. We calculate the 700nm half-maximal intensity minus the 500nm half-maximal intensity (dS) as an indicator of relative rod or cone pathway input strength to downstream cells.
Ganglion cells were separated into four classes by their physiological responses: transient ON (tON), sustained ON (sON), transient ON/OFF (tON/OFF), transient OFF (tOFF). ON and OFF responses of tON/OFF cells were considered separately - their mean ON response required 0.75 log units (5.6x) more 700nm light than 500nm to bring the cell to half-maximal activation, whereas their OFF responses had a mean dS of only -0.1 log units. The dS in tON responding cells had a mean value of 0.60, and tOFF had a dS of -0.49. For the sustained ON responding cells the difference was -0.96, showing a strong preference for 700nm light. Similar relationships between cell classes were seen in retinas where all cell types were recorded simultaneously.
Cells with a transient ON component received significant rod pathway input, shown by the 0.75 dS for tON/OFF and 0.60 for tON cells. On the other hand, the sON cells showed a strong preference toward 700nm light with a dS of -0.96. This difference in dS is primarily due to sON cells have a low sensitivity for wide field 500nm light. A strong preference for deep red illumination is not seen in salamander photoreceptors, and so must arise due to subsequent retinal processing. Meanwhile both cell types with tOFF responses were cone dominated, shown by a weak preference for 700nm light. By using multiple electrodes we could control for light adaptational differences between recorded cells. All of the above relationships have therefore been verified, for the first time, by comparison of simultaneously recorded ganglion cells.
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