Central projections of the octavolateralis nerves of the clearnose skate, Raja eglanteria

Abstract

The central projections of first-order lateral line and octavus nerve afferents of the clearnose skate, Raja eglanteria, were determined by nerve degeneration and horseradish peroxidase techniques. The octavolateralis area of the medulla, which receives these afferents, is organized into dorsal, intermediate, and ventral longitudinal columns of cells and neuropil. Fibers that innervate the electroreceptive sense organs enter the dorsal longitudinal column via the dorsal root of the anterior lateral line nerve and terminate within the dorsal nucleus. Mechanoreceptive fibers from neuromasts of the head and trunk are carried by the ventral root of the anterior lateral line nerve and posterior lateral line nerve, respectively. Both nerves enter the intermediate longitudinal column and terminate throughout the rostrocaudal extent of the intermediate nucleus. Fibers of the ventral root of the anterior lateral line nerve are confined to the medial portion of the intermediate nucleus and posterior lateral line nerve fibers to the lateral portion. In addition, ascending mechanoreceptive fibers from both head and trunk neuromasts project to the vestibulolateral lobe of the cerebellum. Octavus nerve afferents enter the medulla and terminate primarily within the four octaval nuclei that comprise the ventral longitudinal column. Rostrocaudally, these nuclei are the anterior, magnocellular, descending, and posterior octaval nuclei. A few ascending axons continue beyond the anterior octaval nucleus and course to the vestibulolateral lobe of the cerebellum. Some descending axons emanate from the descending octaval nucleus and course to the reticular formation and intermediate nucleus. Therefore, electroreceptive lateral line, mechanoreceptive lateral line, and octavus nerve afferents project ipsilaterally and terminate predominantly within separate medullary nuclei. The significance of octavus nerve projections to the intermediate nucleus and overlap of mechanoreceptive and octavus afferents within the vestibulolateral lobe of the cerebellum cannot be determined until it is known which fibers of the inner ear sense organs project to these areas. Retrograde transport of horseradish peroxidase results in the labeling of large multipolar cells, both ipsilaterally and contralaterally, within a column of gray that lies dorsolateral to the reticular formation. These cells are interpreted as the cell of origin of the efferent components of the anterior and posterior lateral line nerves.

The Primary Octaval Nuclei and Inner Ear Afferent Projections in the Otophysan <i>Ictalurus punctatus</i>

“…Although such projections appear to be sparse in some species [McCormick, 1981). in others they may be more substantial [Koester, 1983;Dunn and Koester, 1987;Meredith et a l., 1987;Barry, 1987], In our material, we observe sparse input from the lagena and saccule into the caudal portion of nucleus medialis. The close proximity between the ventral-most border of the ros tral nucleus medialis and the caudo-lateral part of the ante rior nucleus makes it impossible to detemiine whether inner ear inputs terminate in nucleus medialis at these lev els, or conversely, whether lateral line afferents project to the anterior nucleus.…”

“…In Am ia eighth nerve fibers from all otic endorgans project sparsely into nucleus mcdialis, but it is unknown whether they terminate in the Purkinje-likc cell layer, onto other neurons in nucleus mcdialis, or onto the distal dendrites of octaval neurons [McCormick, 1981). This is also the case in various chondrichthyan species [Koester, 1983;Barry. 1987;Dunn and Koester.…”

Primary Projections of the Lateral Line Nerves in Adult Lampreys

“…Primary lateral line fibers have been traced to the dorsal nucleus via the dorsal root of the ALLN in elasmobranchs [Boord and Campbell, 1977;Koester, 1983;Bodznick and Schmidt, 1984], chondrosteans [New and Northcutt, 1984;New and Bodznick, 1985], lepidosirenid lungfishes [Northcutt, 1983], and some urodeles [Fritzsch, 1981]. Electrophysiological recordings indicate that these vertebrates are electroreceptive [Fields and Lange, 1980;Bullock et al, 1983;Münz et al, 1984;New and Bodznick, 1985]; the dorsal nucleus is the primary electrosensory nucleus.…”

“…Peripheral components of lateral line sys tems commonly consist of distinct cranial nerves, the anterior and posterior lateral line nerves (ALLN and PLLN), innervat ing mechanoreceptive neuromasts and, in some cases, one or more types of electrore ceptors. The central projections of the lat eral line nerves to the medullary octavolateralis nuclei have been experimentally ex amined in members of several gnathos-tome radiations: cartilaginous fishes [Boord and Campbell, 1977;Koester, 1983;Bodznick and Schmidt, 1984], lungfishes [Northcutt, 1983], chondrosteans [New and Northcutt, 1984;New and Bodznick, 1985], the bowfin [McCormick, 1981] , salamanders [Fritzsch, 1981], and several species of teleosts [Maler et al, 1973a[Maler et al, , b, 1974Luiten, 1975;Bell and Rus sell, 1978;Claas and Miinz, 1981;Carr et al, 1982;Tong and Finger, 1983;Finger and Tong, 1984;Meredith, 1984], Centrally, primary elctroreceptive afferents terminate separately from fibers supplying mechanoreceptors. Whereas the mechanoreceptive lateral line component appears homologous across the jawed vertebrates, structural and functional characteristics of the receptors, the central projections of the ALLN, and the mor phology of the octavolateralis area all in dicate that electroreception has evolved several times within the lateral line sys tems of gnathostomes [McCormick, 1982;Bullock et al, 1983].…”

The valvula cerebelli of the spiny eel, Macrognathus aculeatus, receives primary lateral-line afferents from the rostrum of the upper jaw

“…This interpretation is supported by evidence that primary lateral-line and octaval projections only reach the vestibulolateral lobe, but no other part of the cerebellum, in the non-teleost actinopterygians Amia (McCormick 1981), and Lepisosteus (Song and Northcutt 1991). Furthermore, in the cartilaginous fish Raja (Koester 1983;Barry 1987), which does not have a valvula, primary octaval and lateral line projections exclusively reach the vestibulolateral lobe and not the corpus cerebelli. The presence of primary lateral-line projections to the valvula cerebelli, in addition to such projections to the eminentia granularis and corpus cerebelli, in the shovelnose sturgeon Scaphirhynchus (New and Nortcutt 1984), can thus also be intepreted as an independently derived feature.…”