Rostrocaudal branching within the climbing fibre projection to forelimb-receiving areas of the cerebellar cortical C1 zone

Abstract

The inferior olive climbing fibre projection to two somatotopically corresponding regions of the paravermal C1 zone in lobule V of the anterior lobe and the rostral folia of the paramedian lobule (PML) in the posterior lobe were investigated in cats by using a combined electrophysiological and retrograde double-labelling technique. In each experiment (n = 7), a small injection of rhodamine-tagged beads was made into the forelimb-receiving part of the C1 zone in one region of the cortex, and an injection of fluorescein-tagged beads was made into the other region. The two regions were found to receive olivary input from cells located in a partially overlapping territory within the rostromedial dorsal accessory olive (DAO). At progressively more rostral levels of DAO, the territory providing climbing fibres to the anterior lobe was centred more laterally than the territory projecting to the rostral PML. Where overlaps occurred, cells that provided climbing fibres to one or the other region were intermingled with a smaller population of double-labelled cells that had axons that branched to supply climbing fibres to both regions of the zone. The double-labelled cells represented on average 26% of the smaller total population of labelled cells within the area of overlap and 7% of the total population of neurones projecting to both regions of the zone. Overall, the findings suggested that the C1 zone within spatially separate but somatotopically corresponding regions of the paravermal cerebellar cortex receives at least partially independent olivary inputs, consistent with the presence of distinct microzones at different rostrocaudal levels of the zone.