Electroretinogram (ERG) flicker photometry was used to examine the photopigment complements of representatives of four genera of Canid: domestic dog (Canis familiaris), Island gray fox (Urocyon littoralis), red fox (Vulpes vulpes), and Arctic fox (Alopex lagopus). These four genera share a common cone pigment complement; each has one cone pigment with peak sensitivity of about 555 nm and a second cone pigment with peak at 430-435 nm. These pigment measurements accord well with the conclusions of an earlier investigation of color vision in the dog, and this fact allows some predictions about color vision in the wild canids. An additional set of measurements place the peak of the dog rod pigment at about 508 nm.

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PubMedDate not supplied

Regional variations in the relative sensitivity to UV light in the mouse retina.

About 3% of all mouse photoreceptors are cones. An earlier electrophysiological study indicated that there were two classes of cone in the mouse retina having peak sensitivities (lambda max) of about 360 nm and 511 nm. Recent immunocytochemical results show there are two types of cones that have distinctive regional segregation patterns. We used regional stimulation of the retina in conjunction with electroretinogram (ERG) flicker photometry to see if the two cone types identified electrophysiologically are regionalized in a fashion suggested by the anatomical results. We find they are. Relative sensitivity to ultraviolet and visible light stimulation qualitatively parallels that predicted by immunocytochemical labelling. One result of this remarkable regionalization of cone types is that the mouse retina is relatively more sensitive to ultraviolet light stimulation when that light is directed toward the ventral half of the retina.

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PubMedDate not supplied

Spectral sensitivity of macaque monkeys measured with ERG flicker photometry.

Macaque monkeys are widely used as a model species for investigations of the biology of human vision. Previous measurements suggest that the cone-based spectral sensitivity of these two primates is greatly similar, but perhaps not identical. We measured the photopic spectral sensitivity of 42 male macaque monkeys from two species (Macaca mulatta, M. fascicularis) using an objective index, electroretinogram flicker photometry. The variations among individuals and between the two species were very small and there was no evidence for any significant cone pigment polymorphism in this sample. There are small but systematic differences in spectral sensitivity between macaque monkeys and equivalently tested human subjects--the monkeys were slightly more sensitive to short wavelengths (< 520 nm) and slightly less sensitive to wavelengths longer than this value. The results obtained from the curve fitting of standard photopigment absorption spectra to the spectral-sensitivity functions suggest that the difference between human and macaque monkey spectral sensitivity principally reflects differences in the relative proportions of the long- and middle-wavelength cones in the retinas of the two species.

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PubMedDate not supplied

Photopigment basis for dichromatic color vision in cows, goats, and sheep.

Electroretinogram (ERG) flicker photometry was used to measure the spectral properties of cones in three common ungulates-cattle (Bos taurus), goats (Capra hircus), and sheep (Ovis aries). Two cone mechanisms were identified in each species. The location of peak sensitivity of an S-cone mechanism varied from about 444 to 455 nm for the three species; analogous values for an M/L-cone were tightly clumped at about 552-555 nm. Each of these three species has the requisite photopigment basis for dichromatic color vision and they are, thus, similar to other ungulates examined earlier.

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PubMedDate not supplied

The topography of rod and cone photoreceptors in the retina of the ground squirrel.

The distributions of rod and cone photoreceptors have been determined in the retina of the California ground squirrel, Spermophilus beecheyi. Retinas were fixed by perfusion and the rods and cones were detected with indirect immunofluorescence using opsin antibodies. Local densities were determined at 2-mm intervals across the entire retina, from which total numbers of each receptor type were estimated and isodensity distributions were constructed. The ground squirrel retina contains 7.5 million cones and 1.27 million rods. The peak density for the cones (49,550/mm2) is found in a horizontal strip of central retina 2 mm ventral to the elongated optic nerve head, falling gradually to half this value in the dorsal and ventral retinal periphery. Of the cones, there are 14 M cones for every S cone. S cone density is relatively flat across most of the retina, reaching a peak (4500/mm2) at the temporal end of the visual streak. There is one exception to this, however: S cone density climbs dramatically at the extreme dorso-nasal retinal margin (20,000/mm2), where the local ratio of S to M cones equals 1. Rod density is lowest in the visual streak, where the rods comprise less than 5% of the local photoreceptor population, increasing conspicuously in the ventral retina, where the rods achieve 30% of the local photoreceptor population (13,000/mm2). The functional importance of the change in S to M cone ratio at the dorsal circumference of the retina is compromised by the extremely limited portion of the visual field subserved by this retinal region. The significance for vision, if any, remains to be determined. By contrast, the change in rod/cone ratio between the dorsal and ventral halves of the retina indicates a conspicuous asymmetry in the ground squirrel's visual system, suggesting a specialization for maximizing visual sensitivity under dim levels of illumination in the superior visual field.

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PubMedDate not supplied

Cone receptor variations and their functional consequences in two species of hamster.

Results from earlier experiments indicate that different species of rodent vary both in the number of cone types found in their retinas and in the spectral sensitivities of the cone pigments. These features have now been examined in two types of hamster commonly used for research purposes: Syrian golden hamsters (Mesocricetus auratus) and Siberian dwarf hamsters (Phodopus sungorus). Electroretinogram (ERG) flicker photometry, behavioral discrimination tasks, and opsin antibody labeling were used to investigate hamster photoreceptors and their visual consequences. Results from the three approaches support the following conclusions: (1) The retinas of both species have an abundant population of rods containing a photopigment with peak sensitivity of about 498-500 nm; (2) Siberian dwarf hamsters have two classes of cone: one with maximum sensitivity in the ultraviolet (c. 360 nm), the other with peak sensitivity closely similar to that of its rod; and (3) Syrian golden hamsters have a class of cone with peak sensitivity at about 506 nm, but they lack a second cone type. Implications of these alternative arrangements are discussed.

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