The origin of high and regular discharge rates of eye-movement-related neurons in the region of the interstitial nucleus of Cajal.

Burst-tonic neurons in the region of the interstitial nucleus of Cajal (INC) that show a close correlation to vertical eye movement have been known to exhibit high and regular discharge rates, not only during fixation in alert animals, but also during sleep. Since they receive major input from vertical semicircular canals, we examined in this study whether or not the source of the high and regular discharge rates was the primary vestibular afferents. Infusion of lidocaine into the middle ear bilaterally resulted in a significant decrease of mean discharge rates and an increase in the coefficient of variation of the mean rates. However, burst-tonic neurons in cats that had received bilateral labyrinthectomy 6 weeks previously still exhibited high and regular discharge rates similar to those of normal cats. These results indicate that high and regular discharges of eye-position-related INC cells are maintained largely by input from primary vestibular afferents in normal cats. However, such characteristic discharges could also be maintained centrally in the brainstem without peripheral vestibular input in labyrinthectomized cats.