Biomedical subjects

S Saszik

Publications and source records attributed to S Saszik.

9 recordsLinked to original sources

PubMed2001

Rod contributions to the electroretinogram of the dark-adapted developing zebrafish.

Anatomical studies of the developing zebrafish retina have shown that rods approach maturity at about 15 days postfertilization (dpf). Past work has examined the photopic spectral sensitivity function of the developing zebrafish, but not spectral sensitivity under dark-adapted conditions. This study examined rod contributions to the dark-adapted spectral sensitivity function of the ERG b-wave component in developing zebrafish. ERG responses to stimuli of various wavelengths and irradiances were obtained from dark-adapted fish at 6-8, 13-15, 21-24, and 27-29 dpf. The results show that dark-adapted spectral sensitivity varied with age. Spectral sensitivity functions of the 6-8 and 13-15 dpf groups appeared to be cone dominated and contained little or no rod contributions. Spectral sensitivity functions of the 21-24 and 27-29 dpf groups appeared to have both rod and cone contributions. Even at the oldest age group tested, the dark-adapted spectral sensitivity function did not match the adult function. Thus, consistent with anatomical findings, the rod contributions to the ERG spectral sensitivity function appear to develop with age; however, these contributions are still not adult-like by 29 dpf, which is contrary to anatomical work. These results illustrate that the zebrafish is an excellent model for visual development.

Animals↗

PubMed2001

The zebrafish as a model visual system.

The zebrafish has become an important vertebrate model in developmental neuroscience because it is a useful model for embryology, developmental biology, and genetic analysis. The similarities of its visual system to that of other vertebrates also make this animal a valuable model in vision science. The anatomical, physiological, and behavioral components of zebrafish visual processing have been studied in adult and in developing zebrafish. Its retinal anatomy continues to develop following hatching, providing an opportunity to correlate the development of retinal structure with visual physiology and behavior. In addition, a number of genetic mutations have been developed which are used to examine the contributions of genetics to visual development and function. This article will provide an overview of studies of zebrafish anatomical, physiological and behavioral processing, and the effects if genetic and environmental manipulations on visual development.

Aging↗

PubMed2001

Constant dark-rearing effects on visual adaptation of the zebrafish ERG.

Anatomical and electrophysiological studies have shown that zebrafish retinal neurons develop in a sequential manner. Several studies have examined the impact of restricted rearing environments on zebrafish visual development, but the results have been mixed. The purpose of this study was to examine the development of light adaptation properties of the zebrafish electroretinogram (ERG), and examine the effects of constant dark rearing on retinal development. Subjects were zebrafish, Danio rerio, reared under normal lighting conditions and zebrafish reared in constant dark from fertilization to 6 days postfertilization (dpf). Increment threshold functions were obtained from a- and b-wave ERG responses from normally reared subjects at different ages and from animals exposed to early constant dark rearing. Dark-reared subjects were tested immediately following constant dark exposure (6-9 dpf) and after exposure to normal cyclic lighting (11-13 dpf). Adult zebrafish were significantly more sensitive at lower background illuminations than were larvae zebrafish. Also, constant dark rearing had a differential effect on the a- and b-wave response measures. Constant dark rearing raised b-wave threshold uniformly across background illuminations, while only producing higher a-wave thresholds at low levels of illumination. These results are consistent with findings in studies on zebrafish retinal development, and may help explain some of the discrepancies across studies examining the effects of restricted rearing.

Aging↗

PubMed2000

Effects of experimental glaucoma in macaques on the multifocal ERG. Multifocal ERG in laser-induced glaucoma.

Multifocal ERGs (MERGs) of 5 adult monkeys (Macaca mulatta) with inner retinal defects caused by laser-induced glaucoma were compared to MERGs from 3 monkeys with inner retinal activity suppressed pharmacologically. MERGs were recorded with DTL fiber electrodes from anesthetized monkeys. Stimuli consisted of 103 equal size hexagons within 17 degrees of the fovea. Stimuli at each location passed through a typical VERIS m-sequence of white (200 cd/m2) and black (12 cd/m2) presentations. In animals with laser-induced glaucoma, visual field sensitivity was assessed by static perimetry using the Humphrey C24-2 full-threshold program modified for animal behavior. Inner retinal (amacrine and ganglion cell) activity was suppressed by intravitreal injection of TTX (4.7-7.6 microM) and NMDA (1.6-5 mM). In normal eyes the first order response (1st order kernel) was larger and more complex, with more distinct oscillations (>60 Hz) in central than in peripheral locations. The 2nd order kernel also was dominated by oscillatory activity. There were naso-temporal variations in both kernels. Pharmacological suppression of inner retinal activity reduced or eliminated the oscillatory behavior, and naso-temporal variations. The 1st order kernel amplitude was increased most and was largest at the fovea. Removed inner retinal responses also were largest at the fovea. The 2nd order kernel was greatly reduced at all locations. In eyes with advanced glaucoma, the effects were similar to those produced by suppressing inner retinal activity, but the later portion of the 1st order kernel waveform was different, lacking a dip after the large positive wave. Visual sensitivity losses and MERG changes both increased over the timecourse of glaucoma, with changes in the MERG being more diffusely distributed across the visual field. We conclude that 1st and 2nd order responses of the primate MERG can be identified that originate from inner retina and are sensitive indicators of glaucomatous neuropathy.

Animals↗

PubMed1999

The effects of temperature on the dark-adapted spectral sensitivity function of the adult zebrafish.

In goldfish and other cold-blooded vertebrates, temperature can influence the rhodopsin/porphyropsin contributions to the rod photoreceptors. This study examined the effects of temperature on the spectral sensitivity function of the dark-adapted zebrafish. Zebrafish were housed in either a warm (28-30 degrees C) or cold (22-25 degrees C) tank prior to testing. Fish were dark-adapted for at least 1 h and electroretinogram (ERG) responses to 200 ms stimuli of various wavelengths and irradiances were obtained. Results show that water temperature affected the spectral sensitivity function of the ERG b-wave. Subjects housed in the warm temperatures had a spectral sensitivity consistent with the rhodopsin absorption curve; however, fish housed in the colder temperatures had a spectral sensitivity function that was the result of a rhodopsin/porphyropsin mixture. In addition, ultraviolet cones (lambda max: 362 nm) contributed to the dark-adapted spectral sensitivity function under both temperature conditions. Consistent with the results from other fish, the dark-adapted visual system of the zebrafish can be influenced by water temperature. The results of this study demonstrate the necessity of maintaining a stable environment when examining the contributions of the photoreceptors to the visual response.

Adaptation, Ocular↗

PubMed1999

Establishing and maintaining a low-cost zebrafish breeding and behavioral research facility.

The purpose of this paper is to describe how to establish and maintain a low-cost zebrafish facility that can be used for both teaching and research purposes. The cost of the facility ranges from about $250 to $1,000, depending on the size of the facility and the experiments that will be conducted. The facility plan presented here also has the advantage that it can be disassembled so that it need not function year-round. A detailed list of supplies and materials is provided, along with detailed instructions on how to set up and maintain the adult and breeding portions of the facility. Finally, there is discussion of some of the general uses of a zebrafish facility, including a variety of procedures that are currently being used in behavioral research with this species.

Animal Husbandry↗

PubMed1999

Effects of abnormal light-rearing conditions on retinal physiology in larvae zebrafish.

PURPOSE: Anatomic studies have found that zebrafish retinal neurons develop in a sequential fashion. In addition, exposure to abnormal light-rearing conditions produces deficits in visual behavior of larvae zebrafish, even though there appears to be little effect of the light-rearing conditions on the gross morphology of the retina. The purpose of this study was to assess the effects of abnormal light-rearing conditions on larvae zebrafish retinal physiology. METHODS: Larvae zebrafish (Danio rerio) were exposed to constant light (LL), constant dark (DD), or normal cyclic light (LD) from fertilization to 6 days postfertilization (dpf). After 6 days, the animals were placed into normal cyclic light and tested at 6 to 8, 13 to 15, and 21 to 24 dpf. Electroretinogram (ERG) responses to visual stimuli, consisting of various wavelengths and irradiances, were recorded. Comparisons were made across the three age groups and the three light-rearing conditions. RESULTS: Deficits from the light-rearing conditions were seen immediately after exposure (6 8 dpf). The LL-condition subjects showed the greatest deficit in the UV and short-wavelength areas and the DD-condition subjects showed a slight deficit across the entire spectrum. At 13 to 15 dpf, the LL and DD groups showed an increase in sensitivity and by 21 to 24 dpf, the groups no longer differed from controls. CONCLUSIONS: Abnormal lighting environments can adversely influence the physiological development of the larvae zebrafish retina. The pattern of damage that was seen in zebrafish is similar to that found in other vertebrates, including higher vertebrates. However, unlike higher vertebrates, the zebrafish appears to be capable of regeneration. This suggests that the zebrafish would be a viable model for light environment effects and neural regeneration.

Animals↗

PubMedDate not supplied

Cone contributions to the photopic spectral sensitivity of the zebrafish ERG.

Microspectrophotometry studies show that zebrafish (Danio rerio) possess four cone photopigments. The purpose of this study was to determine the cone contributions to the zebrafish photopic increment threshold spectral-sensitivity function. Electroretinogram (ERG) b-wave responses to monochromatic lights presented on a broadband or chromatic background were obtained. It was found that under the broadband background condition, the zebrafish spectral-sensitivity function showed several peaks that were narrower in sensitivity compared to the cone spectra. The spectral-sensitivity function was modeled with L - M and M - S opponent interactions and nonopponent S- and U-cone mechanisms. Using chromatic adaptation designed to suppress the contribution of the S-cones, a strong U-cone contribution to the spectral-sensitivity function was revealed, and the contributions of the S-cones to the M - S mechanism were reduced. These results show that the b-wave component of the ERG receives input from all four cone types and appears to reflect color opponent mechanisms. Thus, zebrafish may possess the fundamental properties necessary for color vision.

Adaptation, Physiological↗

PubMedDate not supplied

ERG assessment of zebrafish retinal development.

Research has shown that adult zebrafish have a complex visual system, with two possible opponent mechanisms. Anatomically, zebrafish retina develops in a sequential manner and is immature at hatching. The purpose of the present study was to assess zebrafish retinal development using the electroretinogram (ERG). ERG responses to visual stimuli were obtained from 4-5, 6-8, 13-15, and 21-24 days postfertilization (dpf) zebrafish. Individual waveforms were assessed and compared across the four age groups. Spectral-sensitivity functions were calculated for the a- and b-wave components of the ERG response. Results showed that the ERG waveforms and spectral-sensitivity functions varied with age. While the 21-24 dpf subjects had an ERG waveform that was similar to that of adults, the younger subjects did not. Although there were modest differences in the a-wave spectral sensitivity, substantial differences were found in the b-wave spectral sensitivities across the ages. There was a consistent strong response to ultraviolet wavelengths, while across the remaining parts of the spectrum, there was a gradual increase in sensitivity with age. Also, the 21-24 dpf subjects appear to have adult-like U- and S-cone functions, but were missing the L-M and the M-S opponent mechanisms found in the adult. These results support the findings of the anatomical studies and demonstrate that the zebrafish is a useful model for examining the development of retinal function.

Animals↗