UV-SENSITIVE INPUT TO HORIZONTAL CELLS IN THE TURTLE RETINA

Microspectrophotometry, electroretinography and behavioural studies ha ve indicated that ultraviolet (UV) light contributes to functional vis ion in various vertebrate species. Based on behavioural evidence, this was also suggested for turtle vision. In order to reveal the interact ions underlying detection of UV light in the distal retina, we recorde d intracellularly the photoresponses of cones and horizontal cells in retinas of Pseudemys scripta elegans and Mauremys caspica and calculat ed the action spectra of these cells under different conditions of ada ptation. In the dark-adapted retina, all three types of horizontal cel ls; luminosity-type, red/green chromaticity-type and yellow/blue chrom aticity-type exhibited increased sensitivity in the UV region of the s pectrum, However, chromatic adaptation indicated that only the yellow/ blue chromaticity-type horizontal cells received excitatory input from UV-sensitive cones with peak sensitivity approximate to 360 nm. The e nhanced UV sensitivity of luminosity-type horizontal cells probably re flected the beta-band of the long-wavelength sensitive visual pigment as indicated by the action spectra of dark-adapted L-cones. It is sugg ested that the enhanced UV sensitivity of red/green chromaticity-type horizontal cells reflects the beta-band of the medium-wavelength sensi tive visual pigment. Transmission measurements of the optical media (c ornea, lens and vitreous) indicated that UV vision can be functional u nder normal circumstances.