Contralateral as Well as Ipsilateral Projections to Raccoon Cerebellum from External Cuneate Nuclei and Cell Groups f and x

Abstract

To assess the locations and densities of cells in the dorsal medulla giving rise to ipsilateral versus contralateral projections to the mechanosensory regions of cerebellar cortex in the anterior lobe and paramedian lobule, these cortical regions were injected unilaterally with horseradish peroxidase in each of 5 raccoons. To show injection sites and retrogradely labelled cells in the medulla, sections through the medulla and the cerebellum, in at least two different planes for each, were reacted with tetramethylbenzidine; alternate sections were reacted with cobalt-enhanced diaminobenzidine. Labelled were 60–80% of cells in the ipsilateral and 15–25% of cells in the contralateral external cuneate nuclei, as well as 25–50% of cells in the ipsilateral and the contralateral cell groups f and x near the descending vestibular nucleus.Substantial contralateral, as well as ipsilateral cerebellar projections from external cuneate nuclei and cell group x may be related to development of forelimb dexterity in raccoons, since these nuclei mediate forelimb muscular sensibility. The numerical complementarity of ipsilaterally versus contralaterally projecting cells suggests that they represent two separate populations.