Investigation of Central Mechanisms underlying Compen

The autoradiographic [14C]deoxyglucose method for quantitative determination of local cerebral glucose utilization (LCGU) was used to study the compensatory process following hemilabyrinthec tomy in adult cats. In the critical stage when the cats were uncompensated, LCGU in the deafferented vestibular nuclei was well below that of the intact side. Increased LCGU was seen in contralateral nucleus reticularis parvocellularis, the bilateral nuclei pontis, and the ipsilateral abducens nucleus and its ventral parts. Activity levels in the inferior olive were essentially unchanged. In the cerebellum, the posterior vermis and the nodulofloccular lobe were very active. LCGU in the cerebellar nuclei was not noticeably changed. In the compensatory stage, the rate of LCGU in the deafferented vestibular nuclei had increased to that of the intact side. The increased LCGU was bilaterally evident in the nuclei reticularis parvocellularis, gigantocellularis, and lateralis, and superior colliculus. The posterior ver mis, nodulus, and cerebellar nuclei were active. Destruction of the vermis, fastigial nuclei, and surrounding white matter produced marked im balance during walking and a tremor of the head during feeding. These signs subsided very gradually . Interruption of the transreticular vestibular crossed connection produced severe motor disturbances on standing, walking, and feeding, and normal function was not restored. These findings suggest that vestibular compensation results from the combined activity of many brainstem and cerebellar struc tures, where intervestibular crossed pathways are considered an important factor in compensation.