Morphology and physiology of horizontal cells in the retina of the perch (Perca fluviatilis L.)
Horizontal cells of the perch retina were studied with morphological and physiological techniques. Three types of cone horizontal cells were observed in Golgi preparations and they were called HI, H2, and H3 type cells, according to their morphological characteristics. Analysis of cone-horizontal cell contacts, revealed that HI cells contact red sensitive twin cones and green sensitive single cones, H2 cells contact red sensitive twin cones exclusively, and H3 cells contact exclusively green sensitive single cones. Inter connections of cones by basal processes were also examined; single cone basal processes were found to contact twin cone pedicles, and twin cone basal processes to contact other twin cone pedicles. The spectral sensitivity and spatial organization of horizontal cells were analysed by intracellular recordings. Two types of horizontal cell responses were observed; L-type responses that hyper polarized to light stimuli of all wavelengths, and R/G C-type responses that depolarized to red and hyperpolarized to green stimuli. Correlation of anatomical and morphological results suggests that HI and H2 cells generate L-type responses, and H3 cells generate R/G C-type responses. The R/G cells are hyperpolarized by signals from the green (P5352) sensitive cones and depolarized by a far red (650-670 nm) mechanism. Compared with the red cone pigment (P6I52), the L-type horizontal cell spectral sensitivity curve is narrow and with maximum (650 nm) displaced towards the red end of the spectrum (a pseudopigment spectral sensitivity curve), suggesting that an antagonistic interaction occurs between the two cone types, generating the horizontal cell spectral sensitivity function.