Origin in the medial accessory olive of climbing fibres to the x and lateral c1 zones of the cat cerebellum: a combined electrophysiological/WGA-HRP investigation.

The climbing fibres to the x and lateral c1 zones of the anterior lobe of the cerebellum arise as branches of common stem olivary axons. Anatomical studies have shown that the c1 zone receives its climbing fibres from the dorsal accessory olive (DAO). It has, therefore, been assumed that the x-zone also receives its climbing fibres from this olivary subnucleus. The present study demonstrates that both the x-zone and the lateral part of the c1 zone in fact receive their climbing fibre input from the middle portion of the medial accessory olive (MAO) (approximate antero-postero-levels P10-13). Electrophysiological techniques were used to define the extent of these cerebellar zones and small volumes (15-50 nl) of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were pressure injected into the defined zone. These small pressure injections resulted in injection sites with minimal spread to adjacent zones. The sensitive tetramethylbenzidine (TMB) reaction was used to visualize both the injection site and retrogradely labelled cells in the inferior olive. This combination of electrophysiological and neuroanatomical techniques gave extremely reproducible results. The results suggest that the zone previously named lateral c1 would be better designated cx.