Central neuronal pathways in the lateral line system ofXenopus laevis

Abstract

1. InXenopus laevis Daudin, the primary afferents of the posterior lateral line nerve enter the medulla by paths which are different from those taken by the efferent fibres. In the medulla, the afferents occupy a terminal area near the IVth ventricle. The soma layers in this region are identified as the lateral line nucleus. The somata of the primary afferent fibres are located in the jugular ganglion. 2. The somata of the efferents are located in the region of the nucleus XI. Their axons leave the medulla ventral to the entering afferent fibres and join the posterior lateral line nerve in the jugular ganglion. 3. In the lateral line nucleus, the lateral line sensory input is transferred from primary to secondary neurons. The existence of intrinsic interneurons within the nucleus indicates a more complex kind of information processing. 4. Secondary afferent neurons emerging from the lateral line nucleus project into at least three regions: (a) the opposite lateral line nucleus, (b) the cerebellar region, (c) both the contralateral and ipsilateral mesencephalic torus semicircularis. 5. Suppression of activity of secondary neurons which issue from one lateral line nucleus and proceed to the contralateral torus semicircularis may take place provided that the opposite posterior lateral line nerve was stimulated at least 4 ms earlier than its counterpart.