THE OCTAVOLATERAL SYSTEMS IN THE STINGRAY, DASYATIS-SABINA .1. PRIMARY PROJECTIONS OF THE OCTAVAL AND LATERAL LINE NERVES

The central projections of the electrosensory, mechanosensory, and oct aval nerves of the Atlantic stingray were examined by transganglionic transport of horseradish peroxidase. Particular attention was paid to the relation of the projections to cell plates C1 and C2, and to a new ly described cell plate, C3. The electroreceptors in the stingray are found in three groups on the dorsal and ventral sides of the body. The electroreceptors are represented topographically on the ipsilateral d orsal nucleus. Those of the rostral part of the head and pectoral fins are represented on the rostroventral part of the nucleus, and those o n the caudal part of the head and the pectoral fin on the dorsocaudal part of the nucleus. Mechanosensory lateral line afferents terminate w ithin the ipsilateral intermediate and caudal nuclei, and the lateral granular mass of the vestibulocerebellum.-Anterior lateral line affere nts also project to the magnocellular octaval nucleus. A topographic r epresentation of the mechanosensory lateral line periphery is present on the intermediate and caudal nuclei. Mechanoreceptors on the trunk a re represented laterally and those on the head medially. The terminal field of the anterior lateral line afferents on the intermediate nucle us surrounds cell plates C1 and C2. The anterior lateral line afferent s also project to the medial part of the lateral granular mass, wherea s the posterior lateral line afferents project to the lateral portion. Sparse projections of anterior lateral line afferents to the perivent ricular octaval nucleus were also observed. The octaval nerve afferent s terminate largely within the octaval column. Octaval nerve projectio ns were also observed to the reticular formation, the periventricular octaval nucleus, the deep cerebellar nucleus, the vestibulocerebellum, particularly the lower lip and medial granular mass, and the intermed iate nucleus. A sparse projection to cell plate C3 was found. The rela tion between cell plates C1 and C2 and the anterior lateral line affer ents suggests that these cell plates are related to processing lateral line information. While the relationship between cell plate C3 and th e octaval afferents is not strong, the sparse octaval projection C3 re ceives suggests that it is relaying octaval information.