Tetrachromatic input to turtle horizontal cells

Abstract

Recent physiological experiments support behavioral and morphological evidence for a fourth type of cone in the turtle retina, maximally sensitive in the ultraviolet (UV). This cone type has not yet been included in the models proposed for connectivity between cones and horizontal cells. In this study, we examined the inputs of UV, S, M, and L cones to horizontal cells. We used the high-resolution Dynamic Constant Response Method to measure the spectral sensitivity of horizontal cells without background light and after adaptation to UV, blue (B), green (G), and red (R) light. We concluded the following: (1) Tetrachromatic input to a Y/B horizontal cell was identified. The spectral-sensitivity curves of the cell in three of the adaptation conditions were well represented by L-, M-, and S-cone functions. Adaptation to blue light revealed a peak at 372 nm, the same wavelength location as that determined behaviorally in the turtle. A porphyropsin template could be closely fitted to the sensitivity band in that region, strong evidence for input from a UV cone. (2) The spectral-sensitivity functions of R/G horizontal cells were well represented by the L- and M-cone functions. There was no indication of UV- or S-cone inputs into these cells. (3) The spectral sensitivities of the monophasic horizontal cells were dominated by the L cone. However, the shape of the spectral-sensitivity function depended on the background wavelength, indicating secondary M-cone input. Connectivity models of the outer retina that predict input from all cone types are supported by the finding of tetrachromatic input into Y/B horizontal cells. In contrast, we did not find tetrachromatic input to R/G and monophasic horizontal cells. Chromatic adaptation revealed the spectral-sensitivity function of the turtle UV cone peaking at 372 nm.

Spectral Responses in Zebrafish Horizontal Cells Include a Tetraphasic Response and a Novel UV-Dominated Triphasic Response

“…ERG recordings identify UV cone contributions in zebrafish (Bilotta et al 2005;Hughes et al 1998;Nelson and Singla 2009) and juvenile goldfish (Chen and Stark 1994). Horizontal cell hyperpolarizations to UV light have been reported in turtle (Ammermuller et al 1998;Ventura et al 1999;Zana et al 2001) and fish (Hashimoto et al 1988). Tetraphasic light responses were first described in the 1980s in fish (Fukurotani and Hashimoto 1984;Harosi and Fukurotani 1986;Hashimoto et al 1988); however, with the exception of Japanese dace (Hashimoto et al 1988), we found no reports describing UVpreferring triphasic responses in horizontal cells in any of the above species.…”

“…In turtle, all horizontal cells are hyperpolarized by UV light stimulation (Ammermuller et al 1998;Ventura et al 1999), but only the triphasic cells receive direct UV cone excitation Zana et al 2001). In fish, triphasic horizontal cells also receive inputs from UV cones (Hashimoto et al 1988), and, in some species of cyprinids, a tetraphasic response-hyperpolarized to red, depolarized to green, hyperpolarized to blue, depolarized to UV-has been reported (De Aguiar et al 2006;Fukurotani and Hashimoto 1984;Harosi and Fukurotani 1986;Hashimoto et al 1988).…”

Seeing red to being red: conserved genetic mechanism for red cone oil droplets and co-option for red coloration in birds and turtles

“…By contrast, other extant reptile lineages either lack retinal oil droplets entirely (crocodiles, snakes) or have coloured oil droplets varying from clear to yellow and green, but not red (many lizards) [14]. Like birds, turtles have excellent tetrachromatic colour vision [17,18].…”

Do Hermann's tortoises (Testudo hermanni) discriminate colours? An experiment with natural and artificial stimuli

“…Moreover, most Chelonians exhibit good vision, based on a complex type of eye, which allow them to see and clearly distinguish images and to perceive colours (Granda & Stirling 1965;Ammermüller et al 1995;Twig & Perlman 2004;Mathger et al 2007). Recent physiological experiments have shown that Trachemys dorbignii possess a fourth type of cone in the retina, which is maximally sensitive to the ultraviolet spectrum (Ventura et al 1999;Zana et al 2001).…”