Spinocerebellar projections from the thoracic cord in the cat, as studied by anterograde transport of wheat germ agglutinin‐horseradish peroxidase

The projection fields of the spinocerebellar tracts arising from thoracic segments were studied by the anterograde transport of wheat germ agglutinin bound to horseradish peroxidase (WGA‐HRP) in the cat. Following injections of WGA‐HRP into upper and middle thoracic segments, labeled mossy fiber terminals were seen in all lobules of the anterior lobe, lobules VI, VIII, and IX, sublobule VIIb, the paramedian lobule, medial parts of the dorsal paraflocculus, crus I, crus II, and the simple lobule. In the anterior lobe labeled terminals in sublobules IIb‐Vb accounted for about 50–60% of the total labeled terminals, of which about 14–18% were present in lobule III and 11–13% were present in lobule IV. The labeled terminals were concentrated within 1.0–1.5 mm from the midline in the vermal region, accounting for about 45–75% of the total in each sublobule. Following injections into lower thoracic segments, labeled terminals tended to distribute more numerously in the lateral part of the vermis and the intermediate region. In the posterior lobe about 5% of the total labeled terminals were distributed in lobules VI and VIII, respectively, and about 16–23% were in the paramedian lobule (mainly sublobules B and C). Cases with injections preceded by a lateral cordotomy have shown that about 65% of the total labeled terminals in each lobule of the anterior lobe were distributed ipsilaterally and 35%, contralaterally. In the paramedian lobule the labeled terminals were distributed predominantly ipsilaterally. Projection fields in the horizontal plane were reconstructed from a series of transverse sections through each lobule. In lobules III and IV the labeled terminals were distributed in nine areas: areas 1–4 in the vermis and areas 5–9 in the intermediate‐lateral regions. The two medial areas 1 and 2 were located within 0.5 mm from the midline in zone A1 of Voogd and area 3 appeared to be located in zone A2. Area 4 was located between 0.75 and 1.5 mm in the medial part of zone B. These areas extended longitudinally in the middle part of the apicobasal extent. The five areas in the intermediate‐lateral regions were localized in the basal part of the lobule: area 5 in zone C1, areas 6–8 in zones C2 and C3, and area 9 in zone D. Some of these projection areas were identified also in lobules I, II, and V. In sublobule Villa four distinct longitudinal areas containing labeled terminals were found in the middle part of the apicobasal extent. In the paramedian lobule labeled terminals were distributed in ill‐defined longitudinal areas in the medial and lateral parts of sublobules B (the posterior part) and C (the copular part).