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B.A. Ekesten, P. Gouras; Cone Inputs and Interactions in Murine Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2236.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the strength and polarity of middle (M) and ultra–violet (UV) cone inputs to murine retinal ganglion cells. Methods: Single ganglion cell responses were detected in the retinas of anesthetized C57/BL mice with tungsten micro–electrodes driven through the sclera and vitreous to the neural retina. The retina was stimulated with full field flashes or pulses of ultra–violet (360nm) and green (520nm) light in the presence and absence of a strong steady orange adapting light. Some cells were studied in the dark adapted state. Results: 149 ganglion cells were examined in 36 retinas of 25 mice. Cells could be classified into three groups: (1) Phasic responding cells with no spontaneous activity and large impulse amplitudes; (2) Tonic responding cells with irregular, low frequency (5–10 Hz) spontaneous activity and smaller impulse amplitudes; (3) Metronome–like cells with regular, relatively high frequency (20–30 Hz) spontaneous activity. Every cell encountered was affected by full field stimuli. Types 1 and 2 gave on–, off– or on–off responses. Type 3 gave weaker responses, often only inhibited by turning off a light stimulus. Some cells responded only to UV and others only to M cone inputs. Most cells in the central and upper retina responded to both cone inputs but with different strengths and occasionally different polarities. UV cone inputs occurred throughout the retina, but were predominant in ventral retina. In some cells, the orange adapting light temporarily suppressed the response of UV cones. M cone inputs were found mostly in dorsal retina. In the dark adapted state all cells were much more sensitive to 520 than to 360 nm stimuli and this was considered to be due to rod inputs. Conclusions: Ganglion cells with only UV or only M cone inputs exist in murine retina and are evidence against co–expression of UV and M opsins in all cones. Such cells, as well as those showing UV and M cone responses of opposite polarity, could provide a means for color vision. The existence of phasic and tonic ganglion cell systems implies a functional dichotomy found in other mammalian retinas. The presence of cells spontaneously discharging at relatively high and regular frequencies, and responding to light stimuli, may be unique to murine retina. Light adaptation shifts the sensitivity of most murine retinal ganglion cells toward the ultra–violet in contrast to a long wavelength shift in primates.
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