Reconstruction of Electric Discharge Patterns and Electrogenesis Mechanism in African Sharptooth Catfish Clarias gariepinus (Clariidae, Siluriformes).

Electrical discharges (EDs) in the African sharptooth catfish Clarias gariepinus were studied. Irregular monopolar EDs, lasting for 8-10 ms and longer, and more complex EDs, lasting for 20-50 ms and characterized by specific indentation of the discharge pattern, were recorded in pairs of individuals exhibiting both aggressive and defensive behavior. The pattern of long discharges was reconstructed by adding short EDs with different latencies and amplitudes. The conditions for the formation of long EDs with asynchronous activity of electromotor neurons and the possibility of coordinated operation of the electric generator and electroreceptor systems in catfish were considered, since an increase in the duration of EDs lowers the threshold of their perception.

Electric Organ Discharges of Cyphomyrus petherici (Mormyridae, Osteoglossiformes) from the White Nile Basin.

The waveform and some characteristics of the electric organ discharges have been studied in 11 individuals of Cyphomyrus petherici, the only representative of the genus in the Nilotic fauna. The discharge is characterized by three to five phases with a prevalence of the second phase in terms of the relative amplitude and a wide variability of the total duration of discharge (from 212 to 558 µs). The comparison of the discharges of the species under study with those in the congeneric species and representatives of the genus Pollimyrus (which previously encompassed C. petherici) demonstrates a general similarity of the C. petherici discharges with those of Cyphomyrus, but not Pollimyrus. This is in agreement with the correspondence of the discharge characteristics observed in other mormyrids to the phylogenetic position and taxonomic status of the species.

Electric discharges and electrogenesis peculiarity in two African upside-down catfishes, Synodontis caudovittatus and S. eupterus (Mochokidae, Siluriformes).

The paper reports spontaneous generation of weak electric discharges with an amplitude of 0.4-1.0 mV and a frequency of 3-9 min-1 by solitary Synodontis caudovittatus fish. When fish individuals were tested in pairs, their aggressive-defense interactions were associated with an increase in the amplitude of the discharges (up to 30-45 mV) compared to the discharges of individual fish, while the duration of the pulses increased up to 20-25 ms due to the prolongation of the second phase. In S. eupterus, electric activity was recorded only in the course of aggression-defense interactions, while spontaneous generation of discharges was not observed at all. The paper discusses the different aspects of electrocummunication between the catfish including the role of the reversion of polarity of the merged summated discharges with increased duration.

Electrical discharges in Chinese salamander Andrias davidianus.

In 2-year-old Chinese giant salamanders Andrias davidianus, occasional electric discharges with a characteristic pattern similar to the electric discharges of weakly electric catfish, Polypterus and Protopterus, were recorded for the first time. The discharges markedly differ in shape from the myograms accompanying abrupt movements of the salamander or exceeded them in amplitude by more than an order of magnitude. The discharges were recorded both in the autonomous experiment in the absence of experimenters and at a weak tactile stimulation.

[The functional characteristics of electroreceptive central neurons of the sea catfish Plotosus anguillaris].

With the use of microelectrode techniques (extracellular recordings) and the method of post-stimulus histograms, the functional characteristics of medulla oblongata neurons of sea catfish Plotosus were investigated under stimulation of electroreceptors by a homogeneous electric field of different duration, intensity, and direction. Two types of the cells possessing, accordingly, tonic or phase activity were registered among 66 neurons investigated. The mode of responses (inhibition or acceleration) of tonic neurons to the direction of the applied electric current is typical for central neurons of fresh-water catfish connected with ampullae's electroreceptors. Neurons showing a substantial response to fields of an intensity less than 1 microV/cm were registered. The reactions were most pronounced with the duration of electric stimuli in the range of 20-200 ms; however, particularly sensitive neurons showed distinct responses to stimuli of duration of 5 and even 2 ms. Thus, for the first time a high sensitivity of ampullae's electroreceptors to high-frequency stimulus was discovered, which allows one to expand the range of studying electric signals used by weakly electric fish for electrolocation and communication.

Identification of spinal electromotoneurons in the ray Raja clavata (Rajidae).

Retrograde transport of horseradish peroxidase injected ipsilaterally in several parts of the electric organ and light microscopy were employed to study motoneurons and electromotoneurons of the spinal cord in the weakly electric ray Raja clavata (Rajidae). The horseradish peroxidase-labelled electromotoneurons form a chain of cells located ventrolaterally in the gray matter of the spinal cord segments adjacent to the electric organ. The diameters of cells in the electromotor nucleus vary from 70 to 110 microns. When comparing other motoneurons of the spinal cord with electromotoneurons, the latter reveal no segmentation, whereas motoneurons yield accumulations which are close to metametric ones and are essentially smaller in size (averaging 33 microns in diameter).

[In memory of W. Heiligenberg].

The article is devoted in memory of outstanding neurophysiologist Walter Heiligenberg, worked for many years in the Department of Neurobiology of the Scripps Institution of Oceanography (California, La Hoya). His publications to date exemplify a full understanding of the workings of the brain, perception and processing of sensory signals to them.