A method for evaluating visual impairments using operant behavior in mice

A behavioral method, using a shuttle box (one of the conditioned behaviors) for assessing visual function in mice, was investigated. Normal ICR mice were trained to avoid the unconditioned stimulus (electric footshock) during the presentation of conditioned stimuli (tone and light). After acquisition of avoidance response, normal ICR mice were presented randomly tone or light as the conditioned stimulus. The percent of avoidance in the presentation of light was decreased suddenly, but that of tone was not. However, the decrease of avoidance response to light stimulus was recovered by following trainings. The mice, which had acquired the condition response to tone and light stimulus alone, were treated in their cornea with 4N NaOH. The decrease of percent of avoidance in the mice with alkali-treated cornea after differentiation of conditioned stimuli did not recover following training. These results suggested that visual impairment of mice can be detected by this method. Therefore, we attempted to detect the visual impairments of dominant (Cts) and recessive (cac) hereditary cataract mice, hereditary retina degenerated mice (C3H) and first filial generation mice of C3H, FI ((ICR x C3H) FI). The acquisition curves of both Cts and cac cataract mice were similar to that of normal ICR mice, but those of C3H and FI were similar to that of ICR mice treated with alkali. Moreover, changes in recovery %, which was calculated from avoidance response in the presentation of light alone after differentiation of conditioned stimuli, corresponded to the above results. These findings demonstrated that the visual impairment of Cts and cac cataract mice is weak, while that of C3H and FI mice is strong.