Axonal branching in parasagittal zones of the rat olivocerebellar projection: a retrograde fluorescent double-labelling study

Axonal branching in the olivocerebellar projection was investigated using the retrograde fluorescent double-labelling method. Combinations of true blue and diamidino yellow injections (50 nl) were made in the cerebellar cortex of anaesthetized rats to investigate branching within single longitudinal zones and branching between such zones. The topographical arrangement of the projection was similar to that previously described, but additionally it was found that lateral parts of the inferior olive project more rostrally within a longitudinal zone and medial parts project more caudally in the same zone. Double-labelled olivary neurones, with axons branching rostrally and caudally within a single zone, were found to lie in an intermediate position between the two groups of single-labelled neurones. No such double-labelled neurones occurred when branching between zones was investigated. The correlation between these anatomical findings and earlier physiological work is discussed.