Spinocerebellar projections from spinal border cells in the cat as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The cerebellar projections of spinal border cells, which give rise to crossed ascending axons, were studied in the lower lumbar segments by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. Prior to the injections, the spinal cord was lesioned rostral and ipsilateral to the WGA-HRP injections to eliminate labeling of the ipsilaterally ascending axons. Following injections of WGA-HRP into the L4-L6 segments, labeled terminals were seen in sublobules Ib-Vf of the anterior lobe, sublobules VIf-VIe, lobule VIII, the paramedian lobule, and crus II. More than 90% of the total number of labeled terminals were in the anterior lobe; the projections were predominantly ipsilateral to their cells of origin (about 90% or more labeled terminals of the total number in each of sublobules IIb-Va). Many labeled terminals were seen ipsilaterally in sublobules IIb (11.1-17.5% of the total number), IIIa (11.7-12.9%), IIIb (16.1-17.6%), IVa (8.8-10.8%), IVb (6.2-10.5%), and Va (9.7-10.3%). In the posterior lobe, labeled terminals were numerous only in sublobule C of the ipsilateral paramedian lobule (2.7-4.9%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross-sections through each lobule. In the anterior lobe, labeled terminals were distributed in four major areas. In sublobules IIa-IVa, area 1 was located between 1.0 and 2.0 mm lateral to the midline in zones B-C1 of Voogd; area 2, between 2.0 and 3.0 mm lateral to the midline in zones C1-C2; area 3, between 3.0 and 4.0 mm in zones C2-C3; and area 4, lateral to 4.0 mm from the midline in zone C3. These areas extended apicobasally in the apical to middle parts of the lobules. On the rostral side of sublobule C1 of the ipsilateral paramedian lobule, the projection areas extended in the entire apicobasal and the mediolateral axis of the sublobule, except in the most lateral part. The present results suggest that the SBCs project to specific areas in the cerebellar lobules.