The organization of the turtle inner retina. II. Analysis of color-coded and directionally selective cells.

Color coding and directional selectivity (DS) of retinal neurons were studied in the Pseudemys turtle by using similar intracellular recording and staining techniques as in the preceding paper (J. Ammermüller and H. Kolb, 1995, J. Comp. Neuronal. 358:1-34). Color-coded responses were elicited by red (621 or 694 nm), green (525 or 514 nm), and blue (455 nm) light flashes. In addition to red/green and yellow/blue types of chromaticity horizontal cells, in our sample of 305 identified cells we found that 17% of bipolar cells, 6.5% of amacrine cells, and 18% of ganglion cells exhibit color-coded responses. DS responses were found in 37% of the tested ganglion cells and 41% of the tested amacrine cells. Two morphologically identified bipolar cell types, B10 and B11, were red-ON/blue-OFF and red-OFF/green, blue-ON, respectively. Of five identified amacrine cell types, three were red-OFF/blue-ON center (A1, A3, A23b), one was red-OFF/green-ON center (A32), and one (A33) was double color-opponent of red-ON/blue-OFF center:red-OFF/blue-ON surround. Five ganglion cell types had variously color-coded centers (G14 and G24) or surrounds (G3 and G18), including one type, G6, that was double color-opponent (red-OFF/green-ON center:red-ON/green-OFF surround). Responses to colors were found primarily in sustained responses of bipolar and ganglion cells. However, in amacrine cells, transient components of the response also showed color dependence. Red-OFF-center responses were found in ganglion cells that were in a position to make connections at the strata 2/3 border with the red-OFF bipolar cell (B11); red-ON-center responses occurred in ganglion cells with branches in stratum 4 of the IPL where the red-ON-center bipolar (B10) ended. Blue-ON-center signals appeared to be processed mainly in strata 1-2/3, and blue-OFF-center signals in strata 3-5 of the IPL, with contributions of amacrine cells and bipolar cells. Labeled DS amacrine cells could be identified as A9, A20, and A22, and ganglion cells as G19, G20, and G24. The latter type (G24) showed DS and color coding. All response types (ON-center, OFF-center, ON-OFF) were encountered. DS amacrine cells were monostratified near the middle of the IPL, whereas DS ganglion cells were mono-, bi-, and multistratified, although all DS ganglion cells had one feature in common: they had dendrites in stratum 1 of the IPL.(ABSTRACT TRUNCATED AT 400 WORDS)