Relationship of complex spike synchrony bands and climbing fiber projection determined by reference to aldolase C compartments in Crus IIa of the rat cerebellar cortex

Synchronous complex spike (CS) activity occurs most often among cerebellar Purkinje cells located in a narrow longitudinal (parasagittal) strip of cortex (synchrony band). The relationship of the anatomical organization of the olivocerebellar projection to these synchrony bands has not been investigated in detail. Thus, we studied this relationship by using the aldolase C (zebrin II) expression pattern, another landmark for the cerebellar longitudinal organization, as a reference frame in rat crus IIa. Crus IIa consists of 10 aldolase C-positive and -negative longitudinal compartments. Aldolase C labeling after multiple-electrode recording of CSs indicated that in lateral crus Ila (compartments 5 + to 7 +) synchrony bands were generally constrained to single compartments. In contrast, in medial crus Ila (compartments 4a- to 5a-) the synchrony within and across the compartments was much higher than in lateral crus Ila, resulting in wide synchrony bands covering multiple compartments. Retrograde labeling of olivary neurons by injections of biotinylated dextran amine into aldolase C compartments in crus Ila showed that compartments in medial crus Ila were all innervated by the caudal part of the medial accessory olive. On the other hand, each aldolase C compartment in the lateral crus Ila was innervated by a region in a different submicleus in the rostral inferior olive. These regions in different subnuclei were located close to each other. These results suggest that CS synchrony bands reflect the olivocerebellar compartmental projection pattern and neuronal coupling within a particular olivary submicleus, and that medial and lateral crus Ila may be functionally distinct.