ORGANIZATION OF INNER-EAR ENDORGAN PROJECTIONS IN THE GOLDFISH, CARASSIUS-AURATUS

Cytoarchitectural analysis of the octavolateralis area of the goldfish , Carassius auratus, reveals that as in other teleosts, five first-ord er octaval nuclei are present: the anterior octaval, magnocellular, de scending, tangential, and posterior octaval nuclei. The descending nuc leus appears to be anatomically specialized relative to that of the ha lecomorph Amia calva and many teleosts in that a large dorsomedial sub population of the nucleus lies medial to nucleus medialis, a first-ord er lateral line nucleus. In addition to this dorsomedial zone, the des cending nucleus is made up of an intermediate and a ventral zone. Appl ication of horseradish peroxidase (HRP) to individual inner ear endorg ans reveals that the distribution of these afferents to the octaval nu clei is generally ally similar to that in another otophysan, Ictalurus punctatus [McCormick and Braford, 1993]. Nucleus magnocellularis rece ives a diffuse projection from all of the endorgans. The semicircular canals project heavily to the nucleus tangentialis, the entire ventral zone and portions of the intermediate zone of the descending nucleus, the ventral portion of the caudal anterior nucleus, and the bulk of t he rostral anterior nucleus. The macula neglecta projects to the inter mediate zone of the descending nucleus and to ventral locations within the dorsal half of the caudal anterior nucleus. The otolithic endorga ns - the saccule, lagena, and utricle - project, in an overlapping man ner, to the dorsal half of the caudal anterior nucleus and minimally t o the rostral anterior nucleus. The inputs of the otolithic endorgans to the intermediate zone of the descending nucleus are more segregated , though a given region is sometimes supplied by more than one endorga n. The projections of the saccule tend to be concentrated more mediall y than those of the other two endorgans. The dorsomedial zone of the d escending nucleus receives the majority of its primary input from the saccule, and a much smaller input from the lagena, over most of its ro strocaudal extent. At caudal-most levels of the dorsomedial zone, affe rents from the three otolithic endorgans overlap.