Effects of lesion of the interstitial nucleus of Cajal on vestibular nuclear neurons activated by vertical vestibular stimulation.

Experiments were performed in cats anesthetized with nitrous oxide to study the effects of INC lesions on responses of vestibular nuclear neurons during sinusoidal rotations of the head in the vertical (pitch) plane. Responses of neurons in the INC region were recorded during pitch rotations at 0.15 Hz. A great majority of these neurons did not respond to static pitch tilts, and they seemed to respond either to anterior or to posterior semicircular canal inputs with a peak phase lag of 140 deg (re head acceleration). Responses of vestibular nuclei neurons in intact cats were recorded during pitch rotations at the same frequency (0.15 Hz). Neurons that seemed to respond to vertical semicircular canal inputs showed peak phase lags of 90 deg relative to head acceleration, whereas neurons that responded to static pitch tilts showed peak phase shifts near 0 deg. These results indicate that responses of neurons in the INC region lag those of vestibular neurons by about 50 deg, suggesting that the former neurons possess a phase-lagging (i.e. integrated) vestibular signal. Responses of vestibular neurons in cats that had received electrolytic lesions of bilateral INCs 1-2 weeks previously were recorded during pitch rotations at the same frequency (0.15 Hz). Neurons that presumably responded to vertical semicircular canal inputs showed a peak phase lag of 60 deg relative to head acceleration, a significant decrease of the phase lag compared to normal, whereas responses near 0 deg were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)