Projections to lateral vestibular nucleus from cerebellar climbing fiber zones.

1. The olivary projections to the lateral vestibular nucleus (LVN), direct and excitatory through climbing fiber collaterals and indirect and inhibitory through climbing fiber activated Purkinje cells, were investigated in cats with the spinal cord transected at C3 sparing only the contralateral ventral funiculus. In this preparation all spinocerebellar paths are interrupted except the ventral spino-olivocerebellar paths (VF-SOCPs). Three FV-SOCPs responding with different latencies and receptive fields on limb nerve stimulation project to different sagittal zones in the anterior lobe vermis: the a-zone medially and the b-zone laterally in the vermis and the c1-zone in the extreme lateral part of the vermis and the medial part of the pars intermedia. 2. The EPSPs evoked through climbing fiber collaterals and the following IPSPs evoked through climbing fiber activated Purkinje cells were recorded intracellularly from LVN neurons on limb nerve stimulation. Simultaneously the climbing fiber responses evoked in Purkinje cells located in the a-, b- and c1-zones were recorded as positive potentials from the cerebellar surface. 3. Three groups of LVN neurons were distinguished: X neurons (about 20%) which did not receive excitation or inhibition from the olivary paths, aCF neurons (about 5%) which received excitation and inhibition from the olivary path projecting to the a-zone, and bCF neurons (about 75%) which received excitation and inhibition from the olivary path projecting to the b-zone. No LVN neurons were related to the c1-zone. 4. The aCF and bCF neurons occurred intermingled throughout the LVN. The X neurons occurred predominantly in its ventral part. 5. The findings are discussed in relation to a hypothesis of cerebellar organization.