Cone input to horizontal cells in the turtle retina

Abstract

Action spectra were obtained by intracellular recordings from horizontal cells of the retina of turtle ( Pseudemys scripta). Dark-adapted L 1 type horizontal cells received their major input from either red cones or from blue and green cones. With chromatic adaptation, red-cone dominated L 1 cells could be further subdivided on the basis of receptor input. They received input from only red cones (L 1-R), red and green cones (L 1-RG) or all cones, red, green and blue (L 1-RGB). L 1-RG and L 1-RGB cells most likely receive their green-cone input from double cones. C-type horizontal cells were found to be of two types, biphasic and triphasic. Biphasic cells were depolarized by red light and hyperpolarized by green light (C-R/GB). Chromatic adaptation showed that blue and green cones acted together and opposed the activity of red cones. Triphasic C-type cells depolarized to green light and hyperpolarized to blue and red light (C-G /BR). Thus, blue cones acted with red cones and opposed the action of green cones. From these results it is concluded that: (1) red cones are the main determinant in the turtle luminosity system. (2) green cones and blue cones have their major role in the chromaticity system, (3) these results are consistent with the feedback hypothesis for the formation of C-type responses in turtle horizontal cells.