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Photoreceptor layer of salmonid fishes: Transformation and loss of single cones in juvenile fish
Author(s) -
Cheng Christiana L.,
Flamarique Iñigo Novales,
Hárosi Ferenc I.,
RickersHaunerland Jutta,
Haunerland Norbert H.
Publication year - 2006
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.20879
Subject(s) - opsin , biology , absorbance , pigment , rainbow trout , rhodopsin , retina , photopigment , trout , photosensitivity , anatomy , retinal , biophysics , fish <actinopterygii> , biochemistry , optics , chemistry , fishery , chromatography , organic chemistry , neuroscience , physics
The retinas of many vertebrates have cone photoreceptors that express multiple visual pigments. In many of these animals, including humans, the original cones to appear in the retina (which express UV or blue opsin) may change opsin types, giving rise to new spectral phenotypes. Here we used microspectrophotometry and in situ hybridization with cDNA probes to study the distribution of UV and blue cones in the retinas of four species of Pacific salmon (coho, chum, chinook, and pink salmon), in the Atlantic salmon, and in the rainbow/steelhead trout. In Pacific salmon and in the trout, all single cones express a UV opsin at hatching (λ max of the visual pigment ∼365 nm), and these cones later transform into blue cones by opsin changeover (λ max of the blue visual pigment ∼434 nm). Cones undergoing UV opsin downregulation exhibit either of two spectral absorbance profiles. The first is characterized by UV and blue absorbance peaks, with blue absorbance dominating the base of the outer segment. The second shows UV absorbance diminishing from the outer segment tip to the base, with no sign of blue absorbance. The first absorbance profile indicates a transformation from UV to blue phenotype by opsin changeover, while the second type suggests that the cone is undergoing apoptosis. These two events (transformation and loss of corner cones) are closely associated in time and progress from ventral to dorsal retina. Each double cone member contains green (λ max ∼510 nm) or red (λ max ∼565 nm) visual pigment (double cones are green/red pairs), and, like the rods (λ max ∼508 nm), do not exhibit opsin changeover. Unlike Pacific salmonids, the Atlantic salmon shows a mixture of UV and blue cones and a partial loss of corner cones at hatching. This study establishes the UV‐to‐blue cone transformation as a general feature of retinal growth in Pacific salmonids (genus Oncorhynchus ). J. Comp. Neurol. 495:213–235, 2006. © 2006 Wiley‐Liss, Inc.