EFFECTS OF TOLUENE, STYRENE, TRICHLOROETHYLENE, AND TRICHLOROETHANE ON THE VESTIBULO-OCULO AND OPTO-OCULO MOTOR SYSTEM IN RATS

The acute effects of inhalation of four solvents on the central vestibular system of rats were analyzed by recording eye movements upon different stimuli. The dose-response relationship was investigated. Optokinetic stimulation was obtained by placing the animals in front of a surrounding visual pattern, moving at different velocities. The slow-phase eye velocity (SPV) of nystagmus was calculated and divided by the stimulus velocity, giving the gain. All the solvents caused a decrease of the gain. Vestibular stimulation was performed on a turntable by an angular acceleration/deceleration in darkness. The SPV and the duration of the post-stimulatory nystagmus were calculated. The shape of the SPV dose-response curves differed among the four solvents. Toluene, styrene, and trichloroethylene prolonged the duration of nystagmus while trichloroethane did not. A conflicting vestibular and optokinetic stimulation was performed by an angular acceleration/deceleration with a surrounding visual pattern moving with the turntable. All solvents decreased the ability to cancel nystagmus, elicited by vestibular stimulation in conflict with a visual input. Quick movements of the eyes, saccades, were elicited by tactile stimulation. Toluene, styrene, and trichloroethylene changed the generation of the saccades while trichloroethane did not. Most of the findings indicate a common site of action in the central vestibular system, viz., the cerebellar-vestibular circuit. However, within this domain, there are evident differences in the effects among the solvents. This finding, together with previous results obtained in other experimental models of the central nervous system (CNS), suggest that different solvents should be considered as individual compounds. While the current results are consistent with the notion that solvents affect cerebellar-vestibular function, they also demonstrate differences on selected components of this system which may be of concern.