SODIUM ARSANILATE-INDUCED VESTIBULAR DYSFUNCTION IN RATS - EFFECTS ON OPEN-FIELD BEHAVIOR AND SPONTANEOUS ACTIVITY IN THE AUTOMATED DIGISCAN MONITORING-SYSTEM

Vestibular dysfunction was chemically induced in Long-Evans rats by intratympanic injections (30 mg per side) of sodium arsanilate (atoxyl). Following a one-week recovery period the rats were behaviorally assayed for integrity of the labyrinthine systems. All subjects were tested for presence of the air-righting reflex, the contact-righting reflex (by lightly holding a sheet of Plexiglas against the soles of the rat's feet), and body rotation-induced nystagmus. All animals were then tested for their ability to remain on a small (15 × 15 cm) platform. Next, the subjects were given two 10-min open-field tests during which ambulation, rearing, grooming, and defecation responses were recorded. Four to five weeks later all rats were tested twice (60 min per session) in the automated Digiscan Activity Monitor which provides a multivariate assessment of spontaneous motor activity. The rats with vestibular dysfunction (Group VNX) took significantly less time to fall off the platform (p<0.01). They also exhibited significantly more open-field ambulation but fewer rearing responses (ps<0.01). An examination of group correlation coefficients for open-field variables and the platform test scores revealed some interesting group differences (ps<0.05). In the Digiscan tests the atoxyl-treated rats exhibited fewer number of horizontal movements, but increased speed for these movements (ps<0.05). Vertical movements did not differ significantly in incidence, but these movements were greatly reduced in duration (p<0.001). In general, changes in spontaneous behavior observed in the sodium arsanilate-treated rats were consistent with a loss in ability to balance on the two hind feet (during rearing or grooming) and a redirecting of exploratory vertical movement sequences toward horizontal locomotion, especially in the open-field test. The multivariate behavioral assessment available in the Digiscan Activity Monitoring system seems to be especially useful in the examination of behavioral components affected by vestibular dysfunction. © 1990.