Long term goals are to elucidate the central pathways and connections of the electrosensory, mechanosensory and auditory subdivisions of the octavolateralis system of cartilaginous fishes. Thus far, primarily in the clearnose skate, the electrosensory pathways carrying information from the ampullae of Lorenzini (detectors of weak electric fields) and mechanosensory pathways from lateral line neuromasts (detectors of water movements) have been traced from peripheral receptors to medullar and midbrain levels. Furthermore, recent findings reveal that the mesencephalic electrosensory lateral line nucleus projects to the medial pallium of the telencephalon via a posterior lateral thalamic relay center. Mechanosensory pathways beyond the midbrain level are unknown and an auditory pathway remains anatomically unidentified. The immediate goals are to delineate the efferent projections of the mesencephalic mechanosensory center (dorsomedial nucleus) and their relations to electrosensory mesencephalic, diencephalic and telencephalic terminal fields using experimental neuroanatomical methods (horseradish peroxidase, silver degeneration and autoradiography). In addition, descending input to the medullar electrosensory dorsal nucleus and mechanosensory intermediate nucleus will be studied. The rationale is to discover where the electrosensory and mechanosensory modalities of the octavolateralis system are separate and where they communicate with each other and possibly with other sensory systems. Similar experiments will be performed on representatives of different elasmobranchs with different levels of brain organization (clearnose skates, smooth dogfish and spiny dogfish) for the purpose of sampling variations that occur between primitive and advanced species and comparing similarities and differences in order to reveal evolutionary trends among cartilaginous fishes as well as other vertebrate radiations.
