Ultraviolet Radiation (Uvr) on Zebrafish Development While

¶ … Ultraviolet Radiation (UVR) on Zebrafish Development

While global warming represents a threat to humankind by virtue of a reduction in the ozone layer and an increased exposure to ultraviolet radiation in the future (Conscience, Cotton, Schlumpf et al. 2001), researchers have shown that moderate exposure to varying levels of ultraviolet radiation may have some beneficial effects for humans. For example, multiple sclerosis, type 1 diabetes, and, to a lesser degree, rheumatoid arthritis, in the Northern Hemisphere, especially in Western Europe and North America, display a latitudinal gradient in disease frequency, with the prevalence of these disorders increasing at higher latitudes (Lim et al. 2003). Furthermore, ultraviolet germicidal irradiation (UVGI) that occurs in the upper portion of air in a room has been cited as an environmental control measure that could economically reduce exposure to Mycobacterium tuberculosis (MTB) droplet nuclei (Burge, First & Ko 2002).

Rationale for Selecting Zebrafish. The zebra danio (B. rerio) is a popular freshwater aquarium fish that originated in Asia; this fish is small (up to about 1.5 inches long), with dark-blue and silvery longitudinal stripes (Zebrafish 2004). The zebra danio (B. rerio) provides an attractive system to investigate the early-life-stage toxicity stages in a vertebrate at the molecular, cellular, and whole-organism levels.

Further, there is a large body of literature devoted to mechanisms regulating zebrafish embryo development, and a well-characterized morphologic staging series has also been published (Blechinger, Warren, Kuwada and Krone 2002). Moreover, the transparency of the zebrafish embryo permits scientists to easily observe heart bud migration and fusion, making it an ideal model for such studies (Slothick 2000).

Importance of Investigation. According to Lim et al. (2003), the apparent immune-suppressive effect of ultraviolet radiation (UVR) has suggested that this environmental exposure may influence the development of immune-related disorders, including type 1 diabetes mellitus, rheumatoid arthritis (RA), eczema/dermatitis, and asthma. "Ultraviolet radiation (UVR) reaching the earth's surface varies inversely with latitude; UVR is thus a prominent latitude-related environmental factor" (Lim et al. 2003). Recent photoimmunologic studies have also demonstrated that UVR tends to downregulate cellular immunity, attenuating T-helper (Th)1 T-cell-mediated immune responses (Lim et al. 2003).

These responses are believed to be significantly involved in some autoimmune disorders such as MS, type 1 diabetes, and RA. Consequently, UVR could reasonably be expected to be beneficial for these disorders; however, few autoimmune or other immune-related disorders have been assessed ecologically with respect to UVR. The few studies conducted to date though support the possibility of UVR being a protective modulator of immune and autoimmune processes involved in the etiology of such immune disorders (Lim et al. 2003).

Hypothesis. Based on the foregoing perceived beneficial attributes of UVR, the hypothesis of this investigation is that an experimental sample of one hundred zebrafish that are exposed to additional amount of UVR throughout their lives will live longer than a similarly situated control group that does not receive any UVR exposure beyond what is available in the ordinary ambient laboratory light.

Materials and Methods.

Zebrafish source and maintenance. Five hundred adult zebrafish will be obtained from a commercial source and maintained on a 14:10-hour light:dark cycle at 28.5 [degrees] C. And bred for further generations in marbled tanks as described by Westerfield (1993).

Both experiment and control specimens will be fed three times daily with a combination of Freshwater Aquarium Flakefood (Ocean Star International, Inc., Hayward, California) and live brine shrimp (Carolina Biological Supply Co., Burlington, North Carolina).

Care and treatment of all specimens will follow the guidance and practices established by the Tulane University Institutional Animal Care and Use Committee (cited in Mattingly, Mclachlan, and Toscano 2001).

Procedures. The experiment will be conducted over the course of three phases, each lasting until the entire populations of both groups expire, and each of the three experiments will be conducted identically with the sole exception of the amount of time the experimental groups are irradiated.

The control groups will be raised as described above, with no special efforts being made to moderate their UVR exposure levels.

A commercial black light (personal property of the investigator) and a timer will be used to ensure a comparable amount of UVR is used in each group.

The black light will be placed in such a manner that the entire experimental aquarium is irradiated.

The first experimental groups will receive 3-hour doses of UVR constantly throughout the day (3 hours on, 3 hours off).

The second experimental group will receive 2-hour doses of UVR throughout the day (2 hours on, 2 hours off).

The third experimental group will receive 1-hour doses of UVR throughout the day (1 hour on, 1 hour off).

Methods. As specimens from each respective group die, a record will be made of the date of death and which group on the data collection form (sample at Appendix A). When the final specimen from the control group and the experimental group have expired, the aquaria will be sanitized the experiment repeated until three sessions have been completed.