Untitled research work

In stationary animals, which experience rotation of large-field visual pattern, secondary vestibular neurons respond in a direction-selective manner. The total destruction of the flocculus, which sends inhibitory outputs to second-order vestibular neurons, results in impairment of optokinetic nystagmus (OKN). The prevailing hypothesis, based on physiological evidence, claims the vestibulocerebellum to be an essential final link mediating the optokinetic response to the vestibular nuclei.The flocculus, on the other hand, receives visual signals through a climbing fiber pathway and also through a mossy fiber pathway. In the previous report, however, the inferior olive which is a source of the climbing fiber was unrelated to OKN and visual suppression (VS) of caloric nystagmus. The nucleus reticularis tegmenti pontis (NRT) has been suggested to be a likely candidate for prefloccular relay nucleus conveying visual signals for OKN and VS of caloric nystagmus.In the present experiment, major concerns were to elucidate whether the ponto-flocculo-vestibular tract is related to optokinetic responses. To achieve this goal, OKN was evaluated after producing NRT lesions or floccular ablation in 20 cats. After damage to the NRT on the right side, cats could follow optokinetic stimuli, but showed extreme velocity limitation, at lower stimulus velocities. This limitation was alleviated in 3 weeks. After making unilateral flocculectomy, OKN was normal at low surround velocity (<30°/S), but was extremely velocity-limited at higher speeds. This change, however, disappeared rapidly within a week. Based on these datas, we suspect that NRT may be a relay nucleus mediating the visual signals responsible for OKN not to the flocculus but to the vestibular nucleus.