Ascending pathways from the spinal cord in the himé salmon (landlocked red salmon, oncorhynchus nerka)

Abstract

The ascending pathways from the spinal cord of the himé salmon were anterogradely labelled by the cobaltic lysine method, and their courses and terminations were examined. Following application of the cobaltic lysine to the cut end of the spinal cord or injection of the cobalt at the 10th to 15th spinal segment, labelled axons were traced from the spinal cord to various regions in the rhombencephalon and the mesencephalon. The axons ascending from the dorsal funiculus gave off many terminals as they ascended to the lower medulla. This terminal area may be homologous to the nucleus funiculi dorsalis of other vertebrates, although cytoarchitectural differentiation of the area is not evident. The dorsal funicular fibers also formed some terminals in the vagus and glossopharyngeal motor nuclei and the nucleus fasciculi solitarii. The axons arising from the anterolateral funiculus ascended as the common trunk of the lemniscus spinalis. The lemniscus spinalis fibers distributed many axon terminals on their way through the lower medulla, and most probably made synaptic contacts with the peripheral dendrites of the cells of origin of the reticulospinal pathways throughout its rostrocaudal extent. They also projected to all the medullary cranial nerve motor nuclei (V, VI, VII, IX, and X). The rostral continuation of the lemniscus spinalis fibers entered the lemniscus lateralis and gave a rostrocaudally elongated terminal area in the nucleus lateralis of the torus semicircularis.(ABSTRACT TRUNCATED AT 250 WORDS)