Individual larvae of the zebrafish mutant belladonna display multiple infantile nystagmus-like waveforms that are influenced by viewing conditions.

Purpose: Infantile nystagmus syndrome (INS) is characterized by involuntary eye oscillations that can assume different waveforms. Previous attempts to uncover reasons for the presence of several nystagmus waveforms have not led to a general consensus in the community. Recently, we characterized the belladonna (bel) zebrafish mutant strain, in which INS-like ocular motor abnormalities are caused by misprojection of a variable fraction of optic nerve fibers.

Sunscreen for fish: co-option of UV light protection for camouflage.

Many animals change their body pigmentation according to illumination of their environment. In aquatic vertebrates, this reaction is mediated through aggregation or dispersion of melanin-filled vesicles (melanosomes) in dermal pigment cells (melanophores). The adaptive value of this behavior is usually seen in camouflage by allowing the animal to visually blend into the background.

Slc45a2 and V-ATPase are regulators of melanosomal pH homeostasis in zebrafish, providing a mechanism for human pigment evolution and disease.

We present here the positional cloning of the Danio rerio albino mutant and show that the affected gene encodes Slc45a2. The human orthologous gene has previously been shown to be involved in human skin color variation, and mutations therein have been implicated in the disease OCA4. Through ultrastructural analysis of the melanosomes in albino alleles as well as the tyrosinase-deficient mutant sandy, we add new insights into the role of Slc45a2 in the production of melanin.

Analysis of optokinetic response in zebrafish by computer-based eye tracking.

Large-field movements in the visual surround trigger spontaneous, compensatory eye movements known as optokinetic response (OKR) in all vertebrates. In zebrafish (Danio rerio) the OKR is well developed at 5 days post fertilization and can be used in the laboratory for screening of visual performance following genetic manipulations or pharmaceutical treatments. Several setups for measurement of the zebrafish OKR have been described.

Light perception: more than meets the eyes.

Larval zebrafish lacking eyes and pineal organ show elevated activity levels and undirected light-seeking behaviour upon loss of illumination. This behaviour, termed dark photokinesis, is mediated by hypothalamic deep brain photoreceptors expressing melanopsin.

The Usher gene cadherin 23 is expressed in the zebrafish brain and a subset of retinal amacrine cells.

Purpose: To characterize the expression pattern of cadherin 23 (cdh23) in the zebrafish visual system, and to determine whether zebrafish cdh23 mutants have retinal defects similar to those present in the human disease Usher syndrome 1D.

Methods: In situ hybridization and immunohistochemistry were used to characterize cdh23 expression in the zebrafish, and to evaluate cdh23 mutants for retinal degeneration. Visual function was assessed by measurement of the optokinetic response in cdh23 siblings and mutants.

Automated visual choice discrimination learning in zebrafish (Danio rerio).

Training experimental animals to discriminate between different visual stimuli has been an important tool in cognitive neuroscience as well as in vision research for many decades. Current methods used for visual choice discrimination training of zebrafish require human observers for response tracking, stimulus presentation and reward delivery and, consequently, are very labor intensive and possibly experimenter biased. By combining video tracking of fish positions, stimulus presentation on computer monitors and food delivery by computer-controlled electromagnetic valves, we developed a method that allows for a fully automated training of multiple adult zebrafish to arbitrary visual stimuli in parallel.

VisioTracker, an innovative automated approach to oculomotor analysis.

Investigations into the visual system development and function necessitate quantifiable behavioral models of visual performance that are easy to elicit, robust, and simple to manipulate. A suitable model has been found in the optokinetic response (OKR), a reflexive behavior present in all vertebrates due to its high selection value. The OKR involves slow stimulus-following movements of eyes alternated with rapid resetting saccades.

Distinct retinal deficits in a zebrafish pyruvate dehydrogenase-deficient mutant.

Mutations in ubiquitously expressed metabolic genes often lead to CNS-specific effects, presumably because of the high metabolic demands of neurons. However, mutations in omnipresent metabolic pathways can conceivably also result in cell type-specific effects because of cell-specific requirements for intermediate products. One such example is the zebrafish noir mutant, which we found to be mutated in the pdhb gene, coding for the E1 beta subunit of the pyruvate dehydrogenase complex.

Polarizing optics in a spider eye.

Many arthropods including insects and spiders exploit skylight polarization for navigation. One of the four eye pairs of the spider Drassodes cupreus is dedicated to detect skylight polarization. These eyes are equipped with a tapetum that strongly plane-polarizes reflected light.

Visual acuity in larval zebrafish: behavior and histology.

Background: Visual acuity, the ability of the visual system to distinguish two separate objects at a given angular distance, is influenced by the optical and neuronal properties of the visual system. Although many factors may contribute, the ultimate limit is photoreceptor spacing. In general, at least one unstimulated photoreceptor flanked by two stimulated ones is needed to perceive two objects as separate.

Behavioral neurobiology: how larval fish orient towards the light.

Orientation of animals towards or away from light is a simple behavior commonly found in the animal kingdom. A recent study using zebrafish larvae has revealed the underlying neural logic of this primal choice behavior, by differential use of the retinal ON- and OFF-pathways.

Quantitative measurements of the optokinetic response in adult fish.

Small teleost fish are increasingly used for studying the genetic basis of vision. In particular, zebrafish (Danio rerio) and medaka (Oryzias latipes) are commonly used vertebrate model organisms in developmental research, including research on the development of visual function. A multitude of behavior-based visual tests are established for larvae that have been successfully used to identify and characterize visual defects in genetically manipulated strains of these species.