Biomedical Engineering Reference
In-Depth Information
Camera
Dissecting
microscope
Figure 15.4
A schematic of the
OKR apparatus. A projector plays a
movie of black and white grating
onto the inside of the drum, which
surrounds a dish containing the
8dpf zebrafish larvae immobilized
in methylcellulose (inset). A
camera records movies of the
larvae for subsequent analysis of
eye position and quantification of
the number of saccades for the eye
of each larva.
Drum
Larvae in dish
Glass plate
Projector
zebrafish (partial optokinetic nystagmus (poa)) using gratings illuminated with long-
wavelength red instead of white light (Brockerhoff et al., 1997).
15.3.2.1 OKR Method The MTC for the compound is first determined as
described in Section 15.3.1.1. The zebrafish larvae are treated with compound in
1% (v/v) DMSOfinal solvent concentration in swimmingmedium for 5 days from3 to
8dpf with compound refreshment at 6dpf before assessment by OKR. The OKR assay
is undertaken by immobilizing groups of up to 10 zebrafish 8dpf larvae in 4% (w/v)
methylcellulose in a 2.5 cm plastic Petri dish with the dorsal side up, tail toward the
center, and head facing outward, taking care not to introduce air bubbles that would
impede vision. The larvae are allowed to habituate for 10min prior to assessment.
The methylcellulose does not contain test compound but the OKR assessment is
completed within 15 min of the larvae being removed from the compound solution. A
white drum is then placed around the Petri dish and larvae are video-recorded from
above while a movie of vertical black and white gratings is played by projection from
below in a clockwise and then counterclockwise direction inside the drum. The stripes
are run for 1 min in each direction at a speed of 78 cycles/min, 0.05 cycles/degree. Eye
movement of each individual larva is then analyzed by counting the number of
saccades. If the vehicle-treated larvae control scored less than 20 saccades, the
experiment is considered invalid (Richards et al., 2008).
15.3.2.2 OKR Validation Studies The OKR assay can be used to detect the
adverse effects of compounds on visual function. However,
the OKR assay
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