Central projections and motor nuclei of the facial, glossopharyngeal, and vagus nerves in the mormyrid fish Gnathonemus petersii.

Most of the information about the anatomy of the fish's cranial nerves was collected in the first two decades of this century. Experimental analysis of the VIIth, IXth, and Xth cranial nerves by modern tract tracing techniques started about 20 years ago. Several species have been investigated to date, including one species of Agnatha (Myxinoidea), two species of elasmobranchs, and species of some orders of Teleostei like Cyprinidae, Siluriformes, Perciformes, and Gadidae.

[Long ascending fibers in the dorsal column of a teleost fish: a disynaptic pathway connecting sense organs to cerebellum].

In spite of the generally accepted opinion that long ascending proprioceptive and tactile fibers do not occur in the spinal dorsal columns of teleost fish, it was demonstrated with degeneration and axonal transport tracing methods that such dorsal column fibers exist in the teleost fish Gnathonemus petersii. These fibers are in fact common spinal afferent fibers originating in spinal ganglion cells. They connect the peripheral sense organs with the lateral funicular nuclei (Fl2) in which the dorsal column fibers terminate, directly through the dorsal columns.

A well defined spinocerebellar system in the weakly electric teleost fish Gnathonemus petersii. A tracing and immuno-histochemical study.

Long ascending fiber systems were investigated in the spinal cord of a teleost fish, Gnathonemus petersii. Concomitant results of Fink-Heimer degeneration tracing as well as CaBP28K immunohistochemical labelling demonstrate the existence of a well defined direct pathway from the very lowest spinal level to the caudal lobe of the cerebellum. HRP retrograde labelling shows that this pathway originates in a cellular column located in the most ventral part of the lateral column next to the lateral extremity of the ventral horn.

Serotoninergic neurons in the mormyrid brain and their projection to the preelectromotor and primary electrosensory centers: immunohistochemical study.

Serotonin-containing neurons in the brain of the weak-electric fish Gnathonemus petersii (mormyridae, teleostei) were studied with the aid of immunohistochemical labeling. Study of the central serotoninergic innervation was focused on the structures subserving the command of the electric organ and the first central relay of the electrosensory system. In the midline raphe nuclei, serotoninergic neurons formed a column that stretched from the ventral caudal medulla to the dorsal midbrain, ending caudal to the cerebellar peduncle.

The use of Quetol 651 for the post-embedding immunohistochemical demonstration of gamma-aminobutyric acid on semithin sections.

Quetol 651 was used as an embedding medium for the demonstration of gamma aminobutyric acid (GABA) in semithin sections by the peroxidase-anti-peroxidase method. In order to demonstrate the immunoreactivity, the embedding medium was partially dissolved using absolute ethanol containing 0.8-1 M NaOH or KOH for 5-7 min.

Oculomotor system of the weakly electric fish Gnathonemus petersii.

The peripheral and central aspects of the extraocular system were studied in the weakly electric fish Gnathonemus petersii. All six extraocular muscles show a similar composition of large and small fibers grouped characteristically in the proximal and distal regions respectively. The exit of the three extraocular nerves from the brain is similar to that in other vertebrates.

Convergence of electrotonic club endings, GABA- and serotoninergic terminals on second order neurons of the electrosensory pathway in mormyrid fish, Gnathonemus petersii and Brienomyrus niger (Teleostei).

Previous electrophysiological data indicate that the afferent electrosensory impulses conveyed towards the mesencephalon are blocked in the rhombencephalic electrosensory lateral line nucleus (nELL) by the concomitantly occurring EOD (electric organ discharge) command-associated (corollary) discharge. Electron-microscopic observations and anterograde labeling with horseradish peroxidase show that the primary electrosensory fibers terminate with club endings on the adendritic soma of the nELL cells and form gap junctions with the postsynaptic membrane. The remaining part of the soma and the initial segment membrane of nELL cells are covered with a large number of boutons showing chemical synaptic profiles.

The mormyrid brainstem--II. The medullary electromotor relay nucleus: an ultrastructural horseradish peroxidase study.

The medullary relay nucleus of the mormyrid weakly electric fish Gnathonemus petersii is a stage in the command pathway for the electric organ discharge. It receives input from the presumed command or pacemaker nucleus and projects to the electromotoneurons in the spinal cord. Its fine structure and synaptology were investigated by electron microscopy.

New formation of sensory cells in the tuberous organ (Electroreceptor) of Brienomyrus niger (Mormyridae) induced by transection of afferent nerve.

The tuberous organs-cutaneous electroreceptors of the mormyrid fish Brienomyrus niger-were examined, with the light and electron microscope, after sectioning of the afferent nerve of the lateral line. Transection of the afferent nerve leads to the concomitant complete degeneration of all sensory cells, and to a differentiation of new sensory cells from accessory cells, which constitute the platform. Ultrastructural examination of the newly formed sensory cells shows that within a few days these gain the characteristics of normal sensory cells.

The mormyrid mesencephalon. III. Retinal projections in a weakly electric fish, Gnathonemus petersii.

The optic nerve and the retinal projections were studied in a mormyrid fish, Gnathonemus petersii, by using Fink-Heimer, HRP, cobalt labeling, and autoradiographic tracing techniques. The retinal fibers terminate bilaterally in the following places: suprachiasmatic nucleus, dorsolateral optic nucleus, optic nucleus of the posterior commissure, cortical nucleus, ventral pretectal area, optic tectum, and the accessory optic terminal field. The number of uncrossed fibers is relatively high in the suprachiasmatic nucleus, but negligibly small in the other retinal terminal fields.

The mormyrid brainstem. I. Distribution of brainstem neurones projecting to the spinal cord in Gnathonemus petersii. An HRP study.

The sources of the descending spinal tracts were identified in the teleost fish Gnathonemus petersii by retrograde HRP transport. HRP injections were made at two spinal levels, either at level of the caudal end of the dorsal fin, anterior to the electric organ, or at the pectoral fin. In both cases all labeled cells were found in the rhombencephalon and the mesencephalic tegmentum.

Pathways of the electric organ discharge command and its corollary discharges in mormyrid fish.

The motoneurons which innervate the mormyrid electric organ are driven by a descending volley from the medullary relay nucleus. This nucleus does not initiate the electric organ discharge (EOD) but is driven in an obligatory manner by another center, a command nucleus. One goal of the present study was to identify this command nucleus anatomically.

The mormyrid rhombencephalon: I. Light and EM investigations on the structure and connections of the lateral line lobe nucleus with HRP labelling.

The rhombencephalic posterior lateral line lobe nucleus (nLLL) and its connections were investigated in the mormyrid fish Gnathonemus petersii, at light and electron microscopical levels using HRP tracing. The nLLL, constituted on each side of about 1500 large, round shaped, adendritic cells, is located in the intermediate cell and fibre layer exclusively, in the ventrolateral zone of the posterior lateral line lobe. The cells show a complex synaptology: boutons with chemical synapses cover the largest part of the soma and the long initial segment of the axons.

Anatomical study and HRP identification of electromotoneurons and motoneurons in the spinal cord of Gymnarchus niloticus.

Two types of neurons were identified by light and electron microscopy in the spinal cord of Gymnarchus niloticus following HRP injections at different peripheral sites: one, situated in the mediodorsal region, is labelled after injection into the electric organ; the other, situated in the lateroventral region, is labelled in addition after injections extending beyond to the lateral muscle. The cells of the first type, thus shown to be electromotoneurons (EMNs), are spherical and do not have dendritic processes; some of them are connected by somato-somatic gap junctions. The EMNs are surrounded by dense glial processes and embedded in a network of myelinated axons of large diameter.

On the course and origin of cranial nerves in the teleost fish Gnathonemus determined by ortho- and retrograde horseradish peroxidase axonal transport.

By horseradish peroxidase (HRP) labelling the course and origin of the II-X cranial nerves are identified in the teleost fish Gnathonemus petersii. Roots as well as motor and sensory nuclei in the viscero- and somatomotor and somatosensory areas are localised. Earlier data of comparative and experimental anatomical observations are completed, partly confirmed or corrected.

Electrosensory systems in the mormyrid fish, Gnathonemus petersii : special emphasis on the fast conducting pathway.

1. Rhombencephalic and mesencephalic structures involved in electroreception were investigated by electrophysiological methods in the weakly electric fish Gnathonemus petersii. 2.

Rhombo-mesencephalic connections in the fast conducting electrosensory system of the mormyrid fish, Gnathonemus petersii. An HRP study.

Using retrograde horseradish peroxidase (HRP) axonal transport direct rhombo-mesencephalic connections were revealed in Gnathonemus petersii. By HRP injection in the neuropil of the extrolateral mesencephalic ganglion the neurons of the lateral line lobe nucleus were labeled. The pathway is mainly composed of crossed fibers.

Fast conducting electrosensory pathway in the mormyrid fish, Gnathonemus petersii.

A compound action potential of short latency was recorded from the ganglion mesencephali extrolaterale in response to both the fish's own electric organ discharge and electric stimulation of the whole fish or a branch of the posterior lateral line nerve. The time difference between the response in the nerve, 16 mm from its entry into the brain, and the mesencephalic ganglion, which is positioned 10 mm anterior in the CNS, was found to be 1.6 msec.