Fiber connections of the torus longitudinalis in a teleost: Cyprinus carpio re-examined.

Abstract

Fiber connections of the carp torus longitudinalis were re-examined by means of tract-tracing methods. The torus longitudinalis projected mainly to the stratum marginale of the optic tectum, area pretectalis, and corpus cerebelli. The stratum marginale was anterogradely labeled only by biocytin, but not by horseradish peroxidase. Because the stratum is composed of extremely fine axons of the small toral neurons, this may be ascribed to different molecular weights of the tracers. The main afferent sources to the torus longitudinalis were the nucleus subvalvularis, which was located beneath the nucleus lateralis valvulae, the nucleus subeminentialis pars magnocellularis, and neurons along the posterior mesencephalo-cerebellar tract. Some labeled cells also appeared in the area pretectalis, nucleus paracommissuralis, optic tectum, and torus semicircularis. In a previous paper, it was incorrectly reported that the valvula cerebelli was the main source of afferents to the torus longitudinalis. Here we report the reason for the previous mistake in relation to the techniques employed.