Cells of Origin and Terminations of the Trigeminotectal Projection in the cat as Demonstrated with the Horseradish Peroxidase and Autoradiographic Methods

Abstract

Organization patterns of the trigeminotectal projection in the cat were studied with the horseradish peroxidase (HRP) and autoradiographic techniques.
The projection was purely contralateral and most (68%) of the trigeminotectal cells were located in the oral nucleus, particularly in the rostral and ventral parts. Labeled cells in the oral nucleus had somal diameters of 22.8±7.4μm(mean±SD)and were of the ovoid, fusiform, or triangular type. Other trigeminotectal neurons occurred in the principal (7%), interpolar (13%) and caudal (12%) nuclei. On the other hand, many trigeminothalamic neurons occurred contralaterally in the principal nucleus, most of which were small sized (15.4±4.0μm)with round somata. Trigeminospinal neurons were found bilaterally and those in the oral nucleus were somelarger (33.2±3.1μm)and of the multipolar type.
After injection of tritiated leucine into the rostral and ventral parts of the oral nucleus, silver grains of the labeled trigeminotectal fibers were found contralaterally, terminating in the intermediate gray layer of the superior colliculus. The terminals were seen to form columnar patches,100-500μm wide, separaed at 100-300μm intervals. The discontinuous patches of terminals of other collicular afferents than the trigeminotectal projection were discussed with a comment on their morphological features that have been shown by other investigators.