Chronic recording of the vestibulo-ocular reflex in the restrained rat using a permanently implanted scleral search coil.

A technique is described which allows accurate long-term monitoring of eye movements in the rat using permanently implanted scleral search coils. Search coils permanently sutured around the sclera yield vestibulo-ocular reflex (VOR) gain and phase values which are comparable to those reported previously in the literature using acutely implanted coils or electrooculographic electrodes. Considerations related to strain, sex and surgical procedures which permit measurement of responses in the chronically restrained rat are described. VOR gain and phase show a time course to their recovery following the implant surgery, with asymptotic performance typically attained approximately 10 days post-surgically. This technique, with the ability to monitor eye movements over weeks to months, appears ideal for development of rodent models of reflex adaptation which require observation of reflex behavior over extended periods of time. Development of a chronic procedure for monitoring eye movement in rodents is especially important given their initial response to restraint (extensive struggling). Finally, adaptation of this technique to smaller species (e.g., mouse) appears technically feasible which should permit the application of transgenic and knockout techniques to the determination of various vestibular reflex functions requiring long-term monitoring.