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.

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.

Morphology and physiology of the brainstem nuclei controlling the electric organ discharge in mormyrid fish.

The motoneurons to the mormyrid electric organ are driven from the medullary relay nucleus. This nucleus is in turn innervated by an adjacent cell group, nucleus C. The goals of this study were to characterize the morphology and physiology of neurons in these two nuclei, and to test the hypothesis that nucleus C is the command nucleus responsible for initiating the electric organ discharge.

Physicochemical and immunochemical proofs of short-term insulin regulation of hepatic M2 pyruvate kinase.

In isolated rat hepatocytes, the short-term regulation of the M2 pyruvate kinase isozyme by insulin is demonstrated. This hormone dependence, which is a function of dose and incubation time, is checked by the activity of the pyruvate kinase, using enzyme assay, cellulose acetate electrophoresis and electroimmunodiffusion methods.