Visual cells and visual pigments of the river lamprey revisited

Jan 17, 2020Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology

Visual cells and pigments in the river lamprey revisited

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Abstract

The decay of visual pigments in lamprey cones occurs almost 100 times faster than in typical rods.

Short photoreceptors in lampreys are identified as rods, while long photoreceptors are identified as cones.
The lamprey retina exhibits color discrimination within a specific range of light intensities.
The overlap in working intensity ranges of rods and cones may suggest that rod-cone vision is common among vertebrates.
Lamprey rhodopsin shares similarities with visual pigments found in the 'rods' of nocturnal geckos.
Classifying photoreceptors strictly as 'rods' and 'cones' may overlook their genetic, biochemical, and evolutionary distinctions.

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Retinas of the river lamprey Lampetra fluviatilis were studied by microspectrophotometry, electroretinography and single-photoreceptor electrophysiology to reconcile the apparently contradictory conclusions on the nature of lamprey photoreceptor cells drawn in the early work by Govardovskii and Lychakov (J Comp Physiology A 154:279-286, 1984) and in recent studies. In agreement with recent works, we confirmed former identification of short photoreceptors as rods and of long photoreceptors as cones. In line with the results of 1984, we show that within a certain range of light intensities the lamprey retina exhibits "color discrimination". We found that the overlap of working intensity ranges of rods and cones is not a unique feature of lamprey short receptors, and suggest that rod-cone (possibly color) vision may be common among vertebrates. We show that the decay of meta-intermediates in lamprey cones occurs almost 100 times faster than in typical rod metarhodopsins. Rate of decay of metarhodopsins of lamprey rods take an intermediate position between typical rods and cones. This makes lamprey rhodopsin similar to transmuted cone visual pigment in "rods" of nocturnal geckos. We argue that defining various types of photoreceptors as simply "rods" and "cones" may be functionally correct, but neglects their genetic, biochemical and morphological features and evolutionary history.

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Visual cells and visual pigments of the river lamprey revisited

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