Biomedical subjects

Iñigo Novales Flamarique

Publications and source records attributed to Iñigo Novales Flamarique.

6 recordsLinked to original sources

PubMed2006

Photoreceptor layer of salmonid fishes: transformation and loss of single cones in juvenile fish.

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 (lambda(max) of the visual pigment approximately 365 nm), and these cones later transform into blue cones by opsin changeover (lambda(max) of the blue visual pigment approximately 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 (lambda(max) approximately 510 nm) or red (lambda(max) approximately 565 nm) visual pigment (double cones are green/red pairs), and, like the rods (lambda(max) approximately 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).

Adaptation, Ocular↗

PubMed2004

Temporal shifts in visual pigment absorbance in the retina of Pacific salmon.

The visual pigments and photoreceptor types in the retinas of three species of Pacific salmon (coho, chum, and chinook) were examined using microspectrophotometry and histological sections for light microscopy. All three species had four cone visual pigments with maximum absorbance in the UV (lambda(max): 357-382 nm), blue (lambda(max): 431-446 nm), green (lambda(max): 490-553 nm) and red (lambda(max): 548-607 nm) parts of the spectrum, and a rod visual pigment with lambda(max): 504-531 nm. The youngest fish (yolk-sac alevins) did not have blue visual pigment, but only UV pigment in the single cones. Older juveniles (smolts) had predominantly single cones with blue visual pigment. Coho and chinook smolts (>1 year old) switched from a vitamin A1- to a vitamin A2-dominated retina during the spring, while the retina of chum smolts and that of the younger alevin-to-parr coho did not. Adult spawners caught during the Fall had vitamin A2-dominated retinas. The central retina of all species had three types of double cones (large, medium and small). The small double cones were situated toward the ventral retina and had lower red visual pigment lambda(max) than that of medium and large double cones, which were found more dorsally. Temperature affected visual pigment lambda(max) during smoltification.

Aging↗

PubMed2004

Opsin expression: new mechanism for modulating colour vision.

Each cone photoreceptor in the retina responds to light in a limited range of wavelengths, giving it a spectral phenotype. This phenotype is determined by the most prevalent of the photoreceptor's visual-pigment proteins (opsins) and is assumed to remain unchanged during an animal's lifetime. Here we show that in the Pacific pink salmon, Oncorhynchus gorbuscha, single cones can switch their spectral phenotype from ultraviolet to blue by regulating the production of the appropriate opsins as the fish grow older. This photoreceptor plasticity may operate to modulate colour vision as the salmon's lifestyle changes.

Animals↗

PubMed2002

A novel function for the pineal organ in the control of swim depth in the Atlantic halibut larva.

The pineal organ of vertebrates is a photo-sensitive structure that conveys photoperiod information to the brain. This information influences circadian rhythm and related metabolic processes such as thermoregulation, hatching time, body growth, and the timing of reproduction. This study demonstrates extra-ocular light responses that control swim depth in the larva of the Atlantic halibut, Hyppoglosus hyppoglosus. Young larvae without a functional eye (<29 days) swim upwards after an average delay of 5 s following the onset of a downwelling light stimulus, but sink downwards a few seconds later. Older larvae (> or = 29 days), which possess a functional eye, swim immediately downwards (microsecond delay) following the onset of the light stimulus, but proceed to swim upwards several seconds later. These two response patterns are thus opposite in polarity and have different time kinetics. Because the pineal organ of the Atlantic halibut develops during the embryonic stage, and because it is the only centre in the brain that expresses functional visual pigments (opsins) at early larval stages, it is the only photosensory organ capable of generating the extra-ocular responses observed.

Aging↗

PubMed2002

Partial re-incorporation of corner cones in the retina of the Atlantic salmon (Salmo salar).

The distribution of corner (putative ultraviolet-sensitive) cones in the retina of Atlantic salmon was examined from the small juvenile (parr) stage to the adult stage (approaching sexual maturation). Small parr weighing approximately 5 g lacked corner cones everywhere except, mainly, near the dorsal periphery. Large fish ( approximately 5 kg) approaching sexual maturation showed corner cones in other areas of the dorsal retina besides the periphery. These areas, characterized by low resolving power, had similar corner cone densities to analogous areas in the smolt retina, suggesting that corner cones are formed in the periphery and incorporated into the dorsal retina of the Atlantic salmon sometime during the smolt stage. This incorporation is partial both in numbers of cones and in location (only the dorsal retina is affected). These findings contrast with the situation in rainbow trout where corner cones from existing mosaics are only partially lost from the ventral retina, if at all, and where production and incorporation of these cones into the dorsal retina occurs throughout life. Thus, in salmonids, there are at least two different strategies that determine retinal corner cone distributions.

Aging↗

PubMedDate not supplied

Visual pigments and dichroism of anchovy cones: a model system for polarization detection.

The retinas of anchovies have two unique photoreceptor types: "bifid" and "long" cones (Fineran & Nicol, 1976). The outer segments of these cells contain multiple layers of membranes (lamellae) oriented longitudinally (axially). This orientation is distinct from that in all other vertebrate rods and cones, where the lamellae are stacked transversely with their planes perpendicular to the incident light path. Although the common arrangement provides optimal absorption for normally incident light rays, it is also insensitive to the rays' direction of vibration (i.e. their polarization). In contrast, the two mutually perpendicular sets of axially oriented lamellae segregated into bifid and long cones could function as the principal analyzers for linearly polarized light, as previously hypothesized (Fineran & Nicol, 1976, 1978). Here, we report on a microspectrophotometric study that shows (1) the presence of two spectrally distinct visual pigments in the three photoreceptor types of the bay anchovy retina; these are typical vertebrate pigments in that they bleach, when exposed to light, and have absorption spectra like all other vitamin A1-based visual pigments; (2) that the rods and cones exhibit dichroic absorption of light in accordance with their lamellar orientation, and (3) that the two cone types of the retina contain a spectrally indistinguishable pigment with peak absorbance (lambda(max)) around 540 nm, while the rods contain a rhodopsin-like pigment with lambda(max) near 500 nm. Compared to other vertebrates, anchovies are remarkable for using a monochromatic cone system with unusual specializations supportive of a polarization detection system.

Animals↗