Biology Reference
In-Depth Information
light exposure (
5, 52
). In nocturnal animals such as rats the
intensity of light required to induce retinal damage needs to be
only two to three times above the normal room lighting (200-
400 lx) (
50
).
29. The full-field electroretinogram (ERG) is used to evaluate the
electrical response of the retina to light stimulation. The ERG
is a test used worldwide to assess the function of the retina in
humans and animal models. The method is based on the stim-
ulation of the retina with bright light such as a flash produced
by light emitting diodes or lamps. The flash of light evokes a
recordable bi-phasic wave composed by a negative a-wave and
a positive b-wave. The amplitude of the a- and b-waves is used
to evaluate retinal function (
53
).
The ERG recording and analysis require practice. In our
opinion it is necessary for a novice to follow an experienced
operator to set up the whole ERG apparatus, to perform the
recordings and to analyze the data. Extensive practice is also
important to achieve reproducible results.
30. Use the Ganzfeld software to set: (1) the pattern of light stim-
uli (that are generated by the Ganzfeld globe); (2) the intensity
of the background light. Use the ERG2Ch.vi software to: (1)
register and analyze the evoked ERG traces; (2) vary the ERG
amplification; (3) control the background noise. The ERG2Ch.
vi software computerizes the ERG traces and allows their visu-
alization on the oscilloscope in real time.
31. Amplify the ERG traces 10,000 folds (1K gain), set the band
pass-filter at 0.3-1,000 Hz and the notch filter at 50 Hz.
32. Record the scotopic ERG using 12 flashes of increasing inten-
sity starting from 0.0001 to 20.0 cd s/m
2
(candela per second
per square meter). The luminance varies from −4 to +1.3 log
cd s/m
2
and the gap between flashes of different intensities is
0.6 log. To minimize the noise, the operator averages three
ERG traces per stimulus over the indicated luminance range
using a temporal frequency of 0.7 Hz.
33. Record photopic ERGs using a constant background illumina-
tion (50 cd/m
2
) and ten flashes having the same intensity
(20 cd s/m
2
). To minimize the noise, the operator averages the
resulting ten ERG traces at the indicated intensity (20 cd s/m
2
).
34. The scotopic and photopic ERGs can be recorded one after the
other.
35. The amplitudes of the a- and b-waves generated from a single
eye are plotted as a function of the increasing flash intensity.
36. In case a little amount of blood is recovered from the caudal
vein it is also possible to collect it from the jugular vein. Briefly,
anesthetize the rat and lay it flat on its back, shave the fur
Search WWH ::
Custom Search