Biomedical Engineering Reference
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Figure 12.3 Influence of light level on locomotion. Larvae were tested for 30min in one of the two light
levels followed by 20min in dark (denoted by the bar in the lower portion of the figure). Activity increased to
a steady level in light, whichwas reached earlier under the lower light condition. Switching to dark produced
a rapid rise in activity followed by a gradual decline. Dark activity was higher in larvae that had been
exposed to the brighter light condition.
increase in activity on return to darkwas greater in larvae that were exposed to brighter
light. Interestingly, the subsequent decay in dark activity appeared equal under both
lighting conditions.
The effect of light intensity on the level of activity during the return to dark
resembled the effect produced by varying the duration of a constant intensity of light.
These results suggest that it might be possible to investigate visual summation
phenomena using the locomotion of larval zebrafish.
As a result of these preliminary studies, we arranged a testing protocol that
included (1) an initial period of darkness, (2) a period of light, and (3) a return to
darkness. The duration of these periods and the number of cycles (transitions) were
left as variables that depended on the particular experiment. In addition, activity
during the initial dark period was eliminated from further analysis, since it was
considered a period of acclimation, during which the activity was not under the direct
control of the variables we intended to manipulate.
12.6 CHEMICAL EFFECTS ON LARVAL LOCOMOTION
Recent experiments have determined the effects of acute drug administration on larval
locomotion. The intent of these experiments was to administer compounds that are
known to produce effects on the motor activity of laboratory rodents (mice, rats).
We were particularly interested in determining whether similar qualitative effects of
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