Olivocerebellar projection to the cardiovascular zone of rabbit cerebellum

Climbing fiber responses were evoked in the medial vermal cortex of lobule VIIa by stimulation of the contralateral medial accessory olive (MAO) in anesthetized, paralyzed rabbits. Effective stimulating sites were localized in a small medial part of the caudal MAO, at 0.4-1.6 mm rostral from the caudal pole of the MAO (total length of the MAO, 4.2 mm). Stimulation of this MAO area induced depression in renal sympathetic nerve activity and this depressant response disappeared after ablation of lobule VIIa. Following injections of horseradish peroxidase into the small areas of lobule VIb, VIc, VIIa or VIIb, retrogradely labeled cells were found in corresponding small particular regions of the MAO: lobule VIb to the most caudal part, lobule VIc to the next caudal, lobule VIIa to the most rostral within the caudal MAO, and lobule VIIb further rostrally to the intermediate MAO. There was a clear disparity between the medial halves of lobules VI and VII projected from the medial MAO and the lateral halves from the lateral MAO. These results show that climbing fiber projections to lobules VI and VII are topographically organized, and that the medial region of lobule VIIa, related to cardiovascular function, receives climbing fibers from a localized small medial region of the caudal MAO.