Spectral sensitivities of short‐ and long‐wavelength sensitive cone mechanisms in the frog retina

Abstract

ERG mass photoreceptor responses were recorded across the isolated, aspartate-perfused retina of the frog, Rana temporaria, in order to determine spectral sensitivities of cones. Cone responses were distinguished from rod responses by their faster kinetics, and responses from different cone types were isolated by selective background adaptation. Our main finding is that of a novel short-wavelength sensitive cone population peaking at about 431 nm. Further, we find that the sensitivity spectrum of the dominant long-wavelength sensitive cone population fully accounts for the most common type of photopic ganglion cell spectrum. Both can be described by a nomogram with lambda max = 562 nm. This resolves a long-standing apparent conflict between cone absorbance spectra and ganglion cell sensitivities. Including the 502 nm cones previously described by microspectrophotometry, the frog possesses a collection of cones that could support trichromatic photopic vision.

Simultaneous <em>ex vivo</em> Functional Testing of Two Retinas by <em>in vivo</em> Electroretinogram System

“…Cone photoreceptor responses have been isolated previously by so-called double flash technique where a bright probe flash saturating the rods is followed by a test flash at a time when cones have restored their dark-adapted state but rods remain saturated 19,29 . Here we isolated cone-mediated ERG responses (containing both a- and b-wave) in Ames’ media supplemented with 100 μM of barium but not DL-AP4 by using double flash technique (Figure 3).…”

“…Thus, it is hard to find a background light intensity that is bright enough to keep rods saturated without affecting cones. Here we demonstrate an alternative double flash method that takes advantage of both the lower sensitivity and faster recovery kinetics of cones 19,29,30 . In this way it is easier to isolate truly dark-adapted cone-mediated responses.…”

Measurement of thermal contribution to photoreceptor sensitivity

“…Possible changes in saturating response amplitude during the experiment were corrected for by linear interpolation between interleaved intensity-response functions recorded with a reference wavelength. Cone responses were isolated either by selective suppression of rods with steady background light (in two of four frog cone experiments in Table 1), or, in the dark-adapted retina, by stimulation at a ®xed time after a strong blue pre-¯ash, while rods were still saturated but cones had essentially recovered 19 (two experiments). Rod responses were recorded in the darkadapted retina; cone contributions to responses to longer wavelengths were eliminated on the basis of kinetics (Fig.…”

Pronounced heritable variation and limited phenotypic plasticity in visual pigments and opsin expression of threespine stickleback photoreceptors

“…The electrophysiological technique used relied on extracellular recordings from a subset of optic nerve fibres and this limitation, along with restricted illumination of the ventral retina , could easily have resulted in the absence of detected signal from smaller cone populations. Other taxa, like amphibians, also have reduced populations of UV and S cones dispersed throughout the retina (accounting for ~1-6% of all cones) (Chen et al, 2008), and their physiological presence was only revealed following action potential recordings from the entire retina (Koskelainen et al, 1994;Deutschlander and Phillips, 1995). In primates, S cones (expressing a SWS1 opsin) are present in reduced numbers (<10%) compared with other cone types (Roorda et al, 2001), yet play a role in non-foveal vision.…”