Pikeperch horizontal cells identified by intracellular staining.

Micropipettes filled with Procion yellow dye were used to record from and to stain pikeperch horizontal cells intracellularly. Three major types were found: a distal layer (H1) of relatively small cells which were luminosity or L-type; a second and more proximal layer of larger L-type cells (H2); and a third and yet more proximal layer of very stellate chromatic or C-type cells (H3). A few anucleate processes which displayed slow-potentials were found in the proximal area of the inner nuclear layer. Cells of each of the three layers were shown to be cone related by both anatomical and physiological methods. L-type cells were further categorized by the area over which each exhibited spatial summation and the relative sensitivity of each to red and green lights. Receptive field sizes of H2's were found to range from less than 2 mm to greater than 5 mm in diameter, whereas those of the few H1's tested were all less than 2 mm. Results from spectral screening tests indicate that most H1 and H2 cells are maximally sensitive to orange light, whereas the H3 cells hyperpolarize maximally to green and depolarize maximally to red. A small percentage of sampled C-cells displayed an additional depolarization to violet.