Organization of the efferent vestibular nuclei and nerves of the toadfish, Opsanus tau

Afferent and efferent projections of the VIIIth cranial nerve in the lamprey Lampetra japonica

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the VIIIth cranial nerve in the lamprey Lampetra japonica. Ganglion cells of the VIIIth nerve are classified into three types on the basis of their morphology. The central processes of these ganglion cells enter the medulla in two groups: the anterior group (mostly thick fibers) and the posterior group (mostly thin fibers). Afferent fibers mainly terminate within the ipsilateral ventral and octavomotor nuclei of the octavolateralis area and within the granular and molecular layer of the cerebellum. Some fibers terminate in the contralateral cerebellum, the medial and dorsal nuclei of the octavolateralis area, the descending nucleus of the trigeminal nerve, some cranial motor nuclei, and the lateral octavus nucleus, which has not been described previously. This small nucleus is located beneath the descending nucleus of the trigeminal nerve near the obex. Within the ventral nucleus, thin fibers occupy the dorsal part and thick fibers occupy the ventral part. The basic projection pattern of the primary afferents of the VIIIth nerve in the lampreys was similar to that of gnathostome fishes that have been studied to date. Cell bodies of the efferent vestibular neurons are located between the ipsilateral trigeminal motor nucleus and the facial motor nucleus. The lateral location of these cell bodies differs from that of all other fish species that have been studied.

Efferents to the labyrinth of the river lamprey (Lampetra fluviatilis) as revealed with retrograde tracing techniques

The cells of origin of centrifugal fibres to the labyrinth were examined in a jawless vertebrate, the lamprey, with several retrograde tracers (horseradish peroxidase (HRP), fluorescein isothiocyanate (FITC) and rhodamine coupled dextran-amines (FDA and RDA), and cobalt-lysine) that had been applied to the eighth nerve. With all 3 techniques, up to 20 cells were consistently labelled ipsilaterally, adjacent to the Mauthner cell; none were labelled on the contralateral side. The axons of the efferent cells emanate either from lateral dendrites or the perikaryon and course laterally towards the ipsilateral eighth nerve root. The dendrites ramify widely in the basal plate and may thus receive diverse inputs. The same tracers were applied to the lateral-line nerve and afferent fibres were labelled but no efferent cells, thus confirming previous reports. These data suggest that lampreys have an efferent innervation to the labyrinth but not to the lateral line.

Primary projections and efferent cells of the VIIIth cranial nerve in the monitor lizard, Varanus exanthematicus

In order to describe the central relations of both the afferent and efferent components of the VIIIth cranial nerve in one reptile, the methods of anterograde and retrograde axonal transport and anterograde degeneration were used to study the vestibular and cochlear projections and the efferent system of this nerve in Varanus exanthematicus. On the basis of cresyl violet and Klüver-Barrera staining, five vestibular nuclei, four cochlear nuclei, and two clusters of small cells which could not be designated as strictly auditory or vestibular are distinguished. The vestibular nuclei include the nucleus dorsolateralis, nucleus ventrolateralis, nucleus tangentialis, nucleus ventromedialis, and nucleus descendens. The well-developed cochlear nuclear complex includes the nucleus angularis, nuclei magnocellulares medialis and lateralis, and nucleus laminaris. The two cell clusters are located dorsolaterally in the brainstem just ventrolateral to the acoustic tubercle. The primary afferent vestibular fibers coursing in the anterior VIIIth nerve root distribute to the ventral portions of all vestibular nuclei except nucleus ventromedialis, whereas the fibers coursing in the posterior root project to the dorsal portions of these nuclei. In nucleus ventromedialis fibers of both roots do not segregate into ventral and dorsal portions. Other targets of the vestibular fibers are the two cell clusters, the granular layer of the ipsilateral cerebellum, the reticular formation, and the descending trigeminal tract and its nucleus. The primary cochlear fibers coursing in the posterior root terminate in nucleus angularis, nuclei magnocellulares medialis and lateralis, and the inner cell strand of nucleus laminaris. The efferent system is, ipsi- and contralaterally in the brainstem, composed of ventral and dorsal cell groups that extend from the level of the principal abducens nucleus caudally where they overlap with the facial motor nucleus. The fibers, which originate from the contralaterally located efferent cells, course beneath the IVth ventricle to exit the brainstem on the ipsilateral side.

Cholinergic neurons in the brain of a teleost fish (Porichthys notatus) located with a monoclonal antibody to choline acetyltransferase

A monoclonal antibody (Ab8) to choline acetyltransferase (ChAT) was used to locate structures showing ChAT-like immunoreactivity (ChAT-IR) in the brain of a teleost fish, the midshipman (Porichthys notatus). ChAT is the synthetic enzyme for acetylcholine found in neurons using that neurotransmitter; thus ChAT-IR may be interpreted as indicating putative cholinergic activity. Robust staining is seen in all cranial nerve motor nuclei. In addition, the brainstem of Porichthys is distinguished by two other expansive ChAT-IR zones: a sonic motor nucleus, which innervates swimbladder "drum" muscles, and an octavolateralis efferent nucleus, which innervates acoustic, vestibular, and lateral line end organs. Scattered labeled cells are found in several cranial sensory nuclei--the vagal lobe, and the main and descending trigeminal nuclei. ChAT-IR cells form restricted subpopulations in other noncranial nerve nuclei, including the granule cell layer of the cerebellum; superior, medial, and inferior divisions of the reticular formation; the stratum periventriculare of the midbrain's optic tectum; and the nucleus isthmi in the midbrain tegmentum. In the telencephalon, a dense population of ChAT-IR cells is found in the ventral nucleus of area ventralis; terminals and fine fibers are found in the dorsal, medial, and central nuclei of area dorsalis. Together, the data represent the first complete report of ChAT-IR cell bodies in the brain of any nonmammal with the monoclonal antibody Ab8, which has already been extensively used on a variety of vertebrate brains. The results are thus discussed from a comparative viewpoint, considering reports of ChAT-IR in different taxa.

Localization of choline acetyltransferase to somata of posterior lateral line efferents in the goldfish

The somata of posterior lateral line efferents in goldfish have been identified by retrograde transport of horseradish peroxidase. Co-localization of retrogradely transported horseradish peroxidase and choline acetyltransferase, detected by immunohistochemical staining with the monoclonal antibody AB8, supports the view that some lateral line efferent neurons in the goldfish are cholinergic.

Distribution and morphological characteristics of efferent neurons innervating end organs in the ear and lateral line of the European eel

Neurons that provide the efferent innervation to the labyrinthine and lateral line sense organs of the eel were located by applying horseradish peroxidase to branches of the appropriate cranial nerves. Retrogradely labeled neurons were found in a single median column, the octavolateralis efferent nucleus (OEN), located immediately rostral to and overlapping with the facial nucleus of the branchiomotor column. We estimate that on each side of the brain the efferent nucleus contains about 60-70 neurons, most of which supply the ear and the lateral line system of the head. Most neurons (approximately 90%) are ipsilateral to the targets they innervate. There is no crisp topographical order within the nucleus because neurons supplying different end organs intermingle. However, the head lateral line is supplied by rostrally located neurons, and the body system by more caudal neurons. There are no marked differences in cell form between neurons supplying different targets. Most are multipolar, relatively uniform in size, and have extensive dendrites. The dendrites of some cells extend to the contralateral side of the brain. Efferent axons are of small diameter (approximately 3 micron). Two neurons are sufficiently constant in size and location that they can be consistently recognized from fish to fish. Their axons branch to supply more than one target. Nearly all efferent neurons stain for acetylcholinesterase and some, bordering the midline, consistently stain weakly.

Distribution of afferent fibers in the brainstem from end organs in the ear and lateral line in the European eel

Sensory nerve fibers from the lateral line system and labyrinth of Anguilla anguilla were labeled with horseradish peroxidase and traced to various targets in the ipsilateral brainstem. The three rami of the anterior lateral line nerve and the supratemporal ramus of the posterior lateral line nerve form overlapping terminal zones in the ventral portion of nucleus medialis. The posterior lateral line nerve on the body is represented exclusively in the dorsal half of the nucleus medialis. Eighth nerve fibers from the otolithic end organs in the inner ear send fibers into dorsal portions of three octavus nuclei: anterior, magnocellular, and descending, and saccular fibers lie most medial and utricular fibers most lateral. Fibers from vestibular organs, especially the semicircular canals and utricle, end densely in ventral portions of these nuclei and in the tangential nucleus. All labyrinthine sense organs send fibers into the region of a Mauthner-like neuron, and all except the saccule terminate in the reticular formation, tangential nucleus, and eminentia granularis of the cerebellum. Primary sensory input to the octavolateralis efferent nucleus comes only from the labyrinth, and fibers from the saccule alone penetrate the region of efferent neuronal somata. Fibers from labyrinthine end organs except the saccule project to the reticular formation where they may contact the dendrites of efferent somata. Fibers from the lateral line and the eighth nerve overlap most extensively at the rostral pole of the nucleus medialis and in the eminentia granularis of the cerebellum.