Octavolateral projections to the torus semicircularis of the trout, Salmo gairdneri

Microiontophoretic delivery of horseradish peroxidase in the torus semicircularis of the trout resulted in heavy labeling of somata in the rhombencephalic nucleus intermedius octavolateralis and nucleus octavus magnocellularis. In addition some labeled somata were found closely to the fasciculus longitudinalis lateralis and in the diencephalon. Efferents leave the torus to the diencephalon, the tegmentum and the tectum and, via the fasciculus longitudinalis lateralis, to the rhombencephalon and the spinal cord. It is concluded that in the trout the torus receives octaval and lateral line input mainly directly from the octavolateral area in the hindbrain, without involvement of a superior olive.