Functional and antigenic maps in the rat cerebellum: zebrin compartmentation and vibrissal receptive fields in lobule IXa.

The mammalian cerebellum is compartmentalized, both structurally and biochemically, into an array of parasagittal bands. In the adult rat, bands can be shown by immunocytochemical staining of a Purkinje cell subset with the monoclonal antibody antizebrin II. In contrast to the bands revealed by the zebrin II distribution, electrophysiological maps of tactile representations show an apparently quite different organization, a patchwork somatotopy of interwoven small receptive fields. We have compared zebrin II compartmentation with the distribution of vibrissal receptive fields in the dorsal face of lobule IXa. Nine adult rats were studied. Zebrin II immunocytochemistry revealed a zebrin II+ band at the midline (P1+) and three others (P2+, P3+, P4+) arrayed laterally, separated by the P1-, P2-, and P3- bands of unstained Purkinje cells. The only significant source of variability was that P3- was sometimes ill defined, making the P3+ and P4+ difficult to distinguish. Electrophysiological recording in the granular layer of lobule IXa identified two reproducible vibrissal receptive fields on each side of the midline (V1 and V2), with a third, more laterally, identified occasionally (V3). When receptive field maps were constructed and aligned with the zebrin II compartment maps from the same individuals, the V1 receptive field was centered on P1-, V2 on P2-, and V3 on P3-. However, the receptive fields typically extended beyond the P- band into the neighboring P+ to each side. Thus there is a simple, reproducible vibrissal receptive field organization in lobule IXa that bears a constant relationship to the Purkinje cell compartmentation revealed by zebrin II immunocytochemistry. The biochemical parcellation of the cortex may serve to organize the afferent and efferent projection topography and thus to align the sensory and motor maps in the cerebellum.