The cerebellar corticonuclear projection from lobule Vb/c of the cat anterior lobe: a combined electrophysiological and autoradiographic study. II. Projections from the vermis.

The present study is an investigation of the efferent pathways from Purkinje cells within particular sagittal zones of the vermal region of the cat cerebellar cortex. A combined electrophysiological/autoradiographic technique was used, in which a small volume (10-120 nl) of 3H-leucine was injected into the centre of a chosen cortical zone after the mediolateral extent of the zone had been delimited electrophysiologically on the basis of its climbing fibre input. Study of the uptake and orthograde transport of labelled material by the Purkinje cells showed that the smallest injections gave rise to injection sites which were restricted to a single zone and to terminal labelling which was very reproducible between cases. Larger injections usually resulted in spread of labelled material to neighbouring zones but the resultant distribution of terminal labelling was nevertheless consistent with that arising from smaller injections. The x zone, which receives climbing fibre input transmitted from the ipsilateral forelimb via a dorsal funiculus spino-olivo-cerebellar pathway (DF-SOCP), was found to project to the junctional region between nucleus fastigius and nucleus interpositus posterior (NIP). The b zone, which lies laterally in the vermis and receives climbing fibre input transmitted from both forelimbs (and both hindlimbs) via a slower conducting SOCP, was found to project, not to the cerebellar nuclei proper, but to the ipsilateral lateral vestibular nucleus. The projection of the third zone within the vermis, the a zone, was not examined but it is generally agreed that this zone projects mainly to nucleus fastigius.