The pontine projection to the cerebellar vermal visual area studied by means of the retrograde axonal transport of horseradish peroxidase.

Following injections of horseradish peroxidase (HRP) in cerbellar vermal lobules VI, VIIA and B, VIIA and B in the cat, the distribution of labeled cells in the pontine nuclei was mapped in drawings of serial transverse and horizontal sections. The labeled pontine cells are distributed in 4 largely longitudinal columns, situated in the dorsolateral, peduncular, lateral and paramedian pontine nucleus (referred to as columns A, B, C and D, respectively). The majority of afferents to the vermal, visual areas come from colums A and B. To some extent cells projecting to the various sublobules have their preferential location within each column (Fig. 5). The majority of the fibers end in lobule VII. Available data from the literature show that only columns A, D and rostral part of B may be involved in the transmission of visual impulses to the vermal area, since these columns receive afferents from the superior colliculus, the lateral geniculate body and the visual cortex, respectively. The route via the superior colliculus-dorsolateral nucleus appears to be quantitatively the most important. As judged from data on fiber connections, impulses from various sources (inferior colliculus, cerebellar nuclei and "non-visual" parts of the cerebral cortex) are transmitted to certain parts of the 4 columns. The functional importance of this convergence and some general features in the organization of the pons are discussed.