T. Hashikawa

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.

Identification of cells of origin of tectopontine fibers in the cat superior colliculus: An experimental study with the horseradish peroxidase method

The pontine projections from the superior colliculus in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP in the dorsolateral pontine nucleus, where the tectopontine fibers terminate, a fair number of labeled cells are found throughout the rostrocaudal extent of the ipsilateral superior colliculus. Relatively few of the labeled cells are of medium size (25-40 micron in diameter), more than 80% are small (10-25 micron), but no large cells are labeled. The cell bodies giving rise to tectopontine fibers are distributed in tectal layers deeper than the optic stratum (including this), with only a few in the deeper portion of the superficial gray layer. There are only few labelled cells in the relatively large lateral portion of the intermediate and deep gray layers were the largest neurons (more than 40 micron) are located. Most of these presumably belong to the tectoreticular and the tectospinal projections. The tectal neurons, distributed in various collicular layers, are supposed to receive different kinds of information from other parts of the central nervous system, e.g. from the retina, the cerebral cortex, the brain stem reticular formation, the spinal cord etc. The dorsolateral pontine nucleus appears to have a particular function in the integration of the input from the superior colliculus with those from other sources, especially from the inferior colliculus and the auditory cerebral cortex.

Regional and laminar distribution of choline acetyltransferase immunoreactivity in the cat superior colliculus

The pattern of distribution of cholinergic fibers was examined immunohistochemically in the cat superior colliculus by using a monoclonal antibody against choline acetyltransferase (ChAT). In the superficial layers, an obvious immunoreactive zone was found in the rostral two-thirds of the outer portion of the superficial gray layer (SGS), with increasing immunoreactive intensity at the rostral pole of the colliculus. A mesh-like distribution of the immunoreactive fibers was found throughout the deeper portion of this layer with a higher concentration in the caudal levels. In the deeper collicular layers, a number of ChAT-immunoreactive fibers were seen in the outer portion of the intermediate gray layer (SGI) in a patch-like fashion. A few fibers were also immunoreactive in the deeper portion of the SGI and in the medial aspect of the deep gray layer. The density of the immunoreactivity in the deeper layers increased in the caudal levels. After unilateral destruction of the parabigeminal nucleus, the ChAT immunoreactivity was markedly reduced in the rostral aspect of the contralateral SGS, and moderately in the caudal aspect of the ipsilateral SGS.