Pontine projections to crus I and crus II of the cat cerebellum. A horseradish peroxidase study

Abstract

The location of basal pontine nuclei neurons that project to crus I-crus II subdivisions of the ansiform lobule has been studied in the cat by retrograde axonal transport of horseradish peroxidase. It has been found that the folia of crus I receive projections from cell clusters located in the dorsal and ventral sectors of the paramedian nucleus, from cells scattered in the ventral nucleus and from a prominent cell group lying dorsally within the lateral nucleus. Clusters of neurons located in the ventral sector of the paramedian and lateral nuclei and in the centro-caudal extent of the peduncular and dorsolateral nuclei project to the lateral folia of crus II. These projections are bilateral with ipsilateral preponderance for the dorsolateral nucleus. To the intermediate folia of crus II project neurons located in the dorsolateral and lateral nuclei as well as in the centro-dorsal paramedian and ventral nuclei. The medial folia of crus II receive projections from neuronal aggregates located in the middle sectors of the paramedian nucleus, in the lateral sector of the ventral and in the middle sector of the lateral nuclei and from a scattered cell group lying in the dorsolateral nucleus. The most important aspects of these results are: (a) the pontine neuronal groups projecting to the different crus I-crus II subdivisions are largely segregated within common pontine nuclei; (b) the cellular groups projecting to the different areas of the ansiform lobule—from crus I to medial crus II—are caudo-rostrally displaced within the pontine grey; (c) the pontine projections to the lateral part of crus I-crus II are markedly bilateral. From considerations on the afférents to the labeled pontine areas it can be inferred that the outputs of the visual association cortices and of the forelimb-face areas of the sensorimotor cortex are mainly directed to medial crus II while superior colliculus and area 6 outputs are directed to lateral crus II.