Abstract
Purpose: :
To characterize the optokinetic response in normal and retinal degenerate (RD) rats and mice by modulating the grating frequency and rotational speed using a computer-based apparatus.
Methods: :
The optokinetic testing apparatus consists of four computer monitors (13 inch) arranged in a square to form an optokinetic chamber. A java based computer program was used to generate alternate black and white stripes that can be moved across all four computer monitors. The program allows modulation of the stripe width, speed and direction of the movement of the stripes (clockwise vs anti-clockwise). Optokinetic head-tracking response of rats and mice were tested inside the optokinetic chamber. Normal Copenhagen rats (n=6), S334ter-line-3 retinal degenerate rats (n=6), normal C57 mice (n=6) and rd10 mice (n=6) were tested. Grating frequencies ranging from 0.2 cycles/degree to 1.0 cycles/degree with speeds ranging from 0.25 rev/min to 15 rev/min were used. Each animal was tested for 2 minutes, 1 minute in the clockwise direction and 1 minute in the anti-clockwise direction and the head-tracking behavior was scored on a scale of 0-4 based on the level of response.
Results: :
In rats, the maximum optokinetic score was observed at a grating frequency of 0.1 cycles/degree and a speed of 3 rev/min, whereas in mice, the score was maximum at a grating frequency of 0.3 cycles/degree and a speed of 5 rev/minute. The grating frequency and speed that produced the maximum optokinetic score was similar in normal and RD models (both rats and mice). The average maximum optokinetic score was 3.8 in normal rats and 4.0 in normal mice. Considerable decrease in the magnitude of the response was observed in the RD animals (optokinetic scores 2.0 for line-3 rats and 2.56 for rd10 mice).
Conclusions: :
The study demonstrates that, in both rats and mice, there is a specific grating frequency and speed that evokes the maximum optokinetic response, and this is not affected by retinal degeneration. These parameters may be useful in developing optimal testing protocols for measuring optokinetic visual behavior in rodents following various therapeutic interventions.
Keywords: visual acuity • retina • degenerations/dystrophies