Involvement of small-field horizontal cells in feedback effects on green cones of turtle retina.

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Abstract
Light stimuli depolarize green cones of turtle retina through a circuit involving a feedback connection from luminosity horizontal cells (L-HC) to green cones. In turtle retina 2 types of L-HC were distinguished: large-field L-HC and small-field L-HC. The spatial properties of the feedback depolarizations of green cones were compared with those of both large and small-field L-HC. Green cones were effectively depolarized by relatively small spots of red light than by large red annuli. Red light stimulation of the periphery of the receptive field could reduce the depolarizing influence of central red stimuli. These spatial properties greatly differ from those of the large-field L-HC, whereas they strongly resemble those of the small-field L-HC. These results suggest that the small-field L-HC mediate the feedback action on green cones.