Long ascending fibers in the dorsal column of a teleost fish: a disynaptic pathway connecting sense organs to cerebellum]

In spite of the generally accepted opinion that long ascending proprioceptive and tactile fibers do not occur in the spinal dorsal columns of teleost fish, it was demonstrated with degeneration and axonal transport tracing methods that such dorsal column fibers exist in the teleost fish Gnathonemus petersii. These fibers are in fact common spinal afferent fibers originating in spinal ganglion cells. They connect the peripheral sense organs with the lateral funicular nuclei (Fl2) in which the dorsal column fibers terminate, directly through the dorsal columns. In contrast to the dorsal column nuclei of higher vertebrates, the Fl2 nuclei do not project to the diencephalic thalamus but to the caudal lobe and the second lobe (C2) of the corpus cerebelli. Thus, sense organs and cerebellum are connected by a disynaptic pathway. Since the caudal lobe projects directly to the electrosensory lobe, that is, to the target of electrosensory afferents, the presence of a disynaptic pathway in G. petersii suggests the existence of a proprioceptive control of the electrosensory input.