Effect upon eye movements of rabbits induced by severance of mossy fiber visual pathway to the cerebellar flocculus

In albino rabbits the visual mossy fiber pathway to the cerebellar flocculus was interrupted by placing lesions in the nucleus reticularis tegmenti pontis (NRTP). After recovery of more than 3 days, eye movements were tested by means of a television eye tracking system. The optokinetic response (OKR) in one eye induced by sinusoidally moving a vertical slit light on the horizontal plane (2.5° peak-to-peak amplitude) at 0.17-0.033 Hz in front of that eye. In rabbits with unilateral NRTP lesions, the OKR gain was reduced significantly in the eye contralateral to lesions, whereas that in the ipsilateral eye did not differ from control rabbits. The horizontal vestibulo-ocular reflex (HVOR) exhibited no change attributable to NRTP lesions. The operated rabbits were rotated (5° peak-to-peak amplitude) at 0.1 Hz continuously for 3 h, while the slit light was presented to the eye contralateral to the NRTP lesions. During the rotation, the HVOR gain in the test eye increased adaptively as in control rabbits. It is concluded that the visual mossy fiber pathway to the flocculus contributes to the OKR, but not to visually-guided adaptive modification of the HVOR.