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G. Twig, H. Levy, I. Perlman; Physiological Evaluation of Feedback Interactions Between Horizontal Cells and Cones in the Turtle Mauremys Caspica . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4177.
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Purpose: Feedback interactions between L-type horizontal cells and L-cones improves the frequency response of the horizontal cells and their responsiveness to background illumination. Our goal was to assess the physiological manifestation of feedback between Red/Green C-type horizontal cells and M-cones. Methods: Intracellular recordings were conducted in the dark-adapted retina of the turtle Mauremys caspica, from 3 M-cones (MCs), 5 L-cones (LCs), 10 L-type horizontal cells (LHs) and 25 Red/Green (RGHs). MCs were stimulated withn 540nm light, LCs and LHs with 650nm light stimuli and RGH cells were studied with 700nm and 540nm to elicit depolarizing and hyperpolarizing photoresponses respectively. Results: (1) The steady state membrane polarization of LCs, MCs and LHs during long steps of light was about half of the peak response to stimulus onset. In contrast, RGHs exhibited lesser degree of potential recovery during continuous illumination (20-30%). (2) This difference between LHs and RGHs could be reduced by superfusing the retinal with sub-millimolar concentration (0.25mM) of cobalt ions. Under these conditions, the steady state polarization of LHs during continuous illumination was about 70% of the peak responses to onset if illumination. The behavior of RGHs to background illumination was not affected by cobalt ions. (3) LHs response to termination of background light exhibited fast recovery with slight overshot above the dark potential. RGHs responded similarly to termination of a green background but exhibited a large hyperpolarizing wave after termination of bright red background. The magnitude of this wave increased as the duration of red illumination was prolonged. (4) Flickering (0.5sec; 1sec interval) 700nm light stimuli had different effect upon LHs and RGHs. While the LHs responded with steady state hyperpolarization and reduction in the photoresponses similar to a red background, the RGHs responded with steady state hyperpolarization and response augmentation as if a green background was used. Conclusions: These data are consistent with the assumption of strong feedback effect of LHs onto LCs and very weak negative feedback effect of RGHs onto MCs.
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