The ventral spino-olivocerebellar system in the cat. I. Identification of five paths and their termination in the cerebellar anterior lobe

Abstract

1. The spino-olivocerebellar paths ascending through the ventral funiculus (VF-SOCPs) and projecting to the cerebellar anteior lobe were investigated in cats with the spinal cord transected in the third cervical segment sparing only the ventral funiculus on one side. The climbing fibre responses evoked in Purkinje cells by limb nerve stimulation were studied by recording the mass activity at the cerebellar surface or in the molecular layer. 2. Five VF-SOCPs were distinguished on the basis of their receptive fields, response latencies, and projection areas. 3. The projection areas consist of narrow sagittal zones. Three zones (a, b1 and b2) lie in the vermis and extend throughout lobules II--V. Two zones (c1 and c3) lie in the pars intermedia and are restricted to the classical hindlimb area, lobules II--IV. The VF-SOCPs are labelled according to their termination zones: a-VF-SOCP, b1-VF-SOCP, etc. 4. The a-, c1- and c3-paths are activated from the ipsilateral hindlimb, whereas the b1- and b2-paths are activated bilaterally from the forelimbs and hindlimbs, respectively. The latencies of the responses evoked from the ipsilateral hindlimb are relatively short for the c1-path and successively longer for the c3-, b2- and a-paths. 5. The olivary transmission showed fluctuations in efficacy independent for the different VF-SOCPs. The effect of anaesthetics on this transmission also differed between the paths. 6. It is concluded that the five VF-SOCPs relay in different compartments of the inferior olive which are tentatively identified.