[Comparative analysis of the effect of endogenous antibiotic defensin NP-1 and aminoglycoside antibiotic gentamicin on synaptic transmission in receptors of the frog vestibular apparatus].

The effect of human and rabbit neutrophilic defensins NP-1 and amonoglycoside antibiotic gentamicin on the synaptic transmission in the afferent synapse of isolated vestibular apparatus of the frog has been comparatively studied. Both defensins proved active in the concentration range of 0.0001 to 1 nM and efficiently decreased the impulse frequency in the afferent nerve fibers in a concentration-dependent manner.

[Absence of the effect of opioid peptides on muscarine receptors in the frog vestibular apparatus].

We studied the effects of opioid peptide leu-enkephaline, a specific antagonist of acetylcholine receptors atropine, and non-selective opiate antagonist naloxone on synaptic transmission and responses evoked by acetylcholine in semicircular organs of the frog. A decrease in frequency of acetylcholine (0.1-5.

[The effect of L-serine-O-phosphate on synaptic transmission in the afferent synapses of the ampullae of Lorenzini in skates].

Effect of bath-application of L-serine-O-phosphate (SOP) on the resting and evoked activity as well as on responses elicited by L-glutamate (L-GLU), quisqualate (Q), kainate (KA) and N-methyl-D-aspartate (NMDA) were studied at the level of afferent synapses of the ampullae of Lorenzini. SOP blocked the synaptic transmission (threshold concentration 10(-7) mol/l) and inhibited responses elicited by application of L-GLU and NMDA, while Q- and KA-induced responses remained unchanged. The data obtained permit supposing that inhibitory effects of SOP in the afferent synapses of the ampullae of Lorenzini are associated with its action on membrane receptors of the NMDA type.

[Analysis of the effect of quisqualate, N-methyl-D- aspartate and several blockers of amino acid receptors on synaptic transmission in the ampullae of Lorenzini].

Effects of bath-application of quisqualate (Q), N-methyl-D-aspartate (NMDA) and antagonists of NMDA-receptors: D-amino-adipate (AA), 2-amino-4-phosphonobutyrate (APB), 2-amino-5-phosphonovalerate (APV) and Mg2+ as well as acidic amino acid antagonist: D-glutamylglycine (DGG) on the synapse between the electroreceptor cells and afferent fibres were studied in the ampullae of Lorenzini. Q (threshold concentration 10(-8) M) and NMDA (threshold concentration 10(-5) M) strongly excited afferent fibres. Neither AA nor APB influenced the resting and evoked activities.

[Effect of antagonists of excitatory amino acids on synaptic transmission in the electroreceptors (Lorenzini's ampullae) in skates].

Ampullae of Lorenzini isolated from the skate (Raja clavata) have been investigated in vitro electrophysiologically to determine the nature of the transmitter at the synapse between the electroreceptor cells and afferent fibres. Glutamic acid diethyl ester (GDEE), glutamic acid dimethyl ester (GDME), kynurenic acid (KENYA), cis-2,3-piperidine dicarboxylic acid (PDA) reversibly decreased the resting and stimulus-induced activity. These antagonists also blocked postsynaptic responses induced by glutamate and aspartate.

[Analysis of the effect of glutamic acid diethyl ester on synaptic processes in the ampullae of Lorenzini of the skate].

The effects of glutamic acid diethylester (GDEE) on the electrical activity of the ampullae of Lorenzini were studied in skates. GDEE (10(-6)-10(-4) M) caused a decrease in frequency of afferent discharges in all receptors under study. GDEE also reversibly blocked the effects of excitatory amino acids (L-glutamate and L-aspartate).

[Effects of aspartic acid in the electroreceptors of the skate].

To identify the afferent transmitter in ampullary electroreceptors of the marine skates effects of L-aspartic acid (L-ASP) were examined using bath application of the drug. Perfusion of the basal membrane with L-ASP produced an increase in activity in most experiments (threshold concentrations 10(-7) M). L-GLU and L-ASP were identical in their ability to activate the afferents.

[Effect of kainic acid on synaptic transmission in the electroreceptors (ampullae of Lorenzini) of the skate].

Superfusion of the basal membrane of the ampullae of Lorenzini of the skate Raja clavata with 10(-6)-10(-9) M kainic acid produced significant and reversible changes in background firing rate depending on its initial level. When synaptic transmission was abolished by high Mg2+ solution, succeeding superfusion with kainic acid and Mg2+ containing solution restored the background and evoked activity in the afferent fibres. It is suggested that the observed effects of kainic acid on the activity of the ampullae of Lorenzini may be explained mainly by its presynaptic action.

[Effect of gamma-aminobutyric acid, taurine and catecholamines on the synaptic processes in Lorenzini's ampules in Black Sea skates].

Perfusion of the basal membrane of the ampullae of Lorenzini with GABA, taurine or catecholamines produced a reversible decrease in resting and evoked activity in afferent nerve fibers. Picrotoxine, phentolamine and propranolol did not suppress the electrical activity. Our findings exclude GABA, taurine and catecholamines as the transmitters at the ampullary electro-receptorsensory nerve synapses.

[Effect of glutamic and aspartic amino acids on the electrical activity of the ampullae of Lorenzini in skates].

Perfusion of the basal membrane of the Lorenzini ampullae with 10(-4)-10(-6) M L-glutamic amino-acid, irrespective of the concentration of the amino-acid, produced reversible changes in resting firing rate depending only on initial resting rate. D-glutamic and L-aspartic acids exerted inhibitory effects of the electrical activity. The findings are consistent with the opinion that L-glutamic acid is the synaptic transmitter in the Lorenzini ampullae.

[Frequency characteristics of central neurons of the electroreceptor system of the skate in response to exposure to electric and magnetic fields].

Responses of single units to sinusoidal homogenous electrical and magnetic field stimulation were studied in the lateral-line lobes of the skate Raja radiata. The voltage gradient thresholds were in the range of 0.03-10 microV/cm.

[Effect of potassium ions on the electrical activity of ampullae of Lorenzini in the skate].

Effect of different concentration of externally applied K+ on the resting and evoked discharge of the isolated Lorenzini ampullae was studied in skates. It was shown that low K+ or K+-free solutions caused a decrease in the frequency of the afferent discharge. An increase in K+ concentration (6-10 mM) produced a reversible increase in the resting activity, with no effect on the receptor thresholds to electrical stimulation.

[Activity of central neurons of the electroreceptor system of Glyptosternum reticulatum].

Acute experiments with extracellular recording of pulse activity from neurons of lateral lobes of the Turkestan catfish Glyptosternum reticulatum revealed tonic and phasic neurons. Tonic neurons as compared to phasic ones were more sensitive to a potential gradient in water and has spontaneous activity. Phasic neurons had no spontaneous activity, their responses did not depend on the intensity and duration of electric stimuli.

[Electrophysiologic study of the central projections of the ampullae of Lorenzini in the skate].

A large portion of the central nervous system of the skate Raja radiata was examined for responses related to single electroreceptor organs (ampullae of Lorenzini) or their groups. It was shown that electroreceptors project to the anterior lateral lobes of the medulla, caudal portion of the auricles and the mesencephalon. A topographic segregation of electroreceptors (to the anterior lateral lobes) and mechanical lateral afferents (to the posterior lateral lobes) was found.

[Mechanisms of synaptic transmission in the ampullae of Lorenzini in skates].

Effects of Mg2+, L-glutamate (L-GLU) and L-glutamic acid diethyl ester (GDEE) on background and evoked activity of the ampullae of Lorenzini were studied in marine skates (Raja clavata). Perfusion of the basal membrane with 10(-4)-10(-5) M L-GLU produced significant and reversible changes in background firing rate depending on its initial level. When excitability was blocked by perfusion with Mg2+, the background activity could be restored in L-GLU (10(-4)-10(-5) M) Mg2+-containing solution.

[Effect of calcium ions on the electrical and temperature sensitivity of the ampullae of Lorenzini of Black Sea skates].

Changes in the ambient calcium concentration affected similarly both thermal and electrical sensitivity of electroreceptors of the Lorenzini ampullae in the skates. In Ca-free solution containing EGTA the sensitivity first decreased, then increased and after that blocking of synaptic transmission occurred. In Ca-rich solution both thermal and electrical sensitivity decreased.

[Central representation of the anterior lateral line nerve in dwarf catfish].

The central distribution of the anterior lateral line nerve (ramus) (NLLa) were studied in the pygmean sheat-fish (Ictalurus nebulosus) by means of the method of Nauta--Gygax. NLLa, as well as posterior lateral line nerve (NLLp), projects topographically on the nucleus medialis of the acoustic-lateral area. Within the nucleus medialis NLLa can be traces in the rostro-lateral parts.

[Study of the central representation of the posterior nerve of the lateral line in dwarf sheatfish].

Applying the axon-terminal degeneration method, the representation of the lateral line posterior nerve in acustico-lateral area of the dwarf sheatfish medulla oblongata was studied. The connections of the lateral line posterior nerve were demonstrated to be topically organized within the medial nucleus of the acustico-lateral area, however, within the limits of the nucleus the projections were not evenly distributed. The greatest degree of localization of the degenerated terminals was revealed in the dorsolateral area of the medial nucleus on the ipsilateral side, where previously, under adequate stimulation of the organs on the lateral line of the dwarf sheatfish, the greatest amount of responses was registered.

[Magnetic field perception by the electroreceptor system of fish].

Responses of 40 neurons in the acoustic-lateral area to electrical stimuli and changing magnetic induction were studied in the Black Sea skates Dasyates (Trigon) pastinaca. The smallest magnetic induction change which caused a response was 0.8 Gs/s, proving the possibility of perception of the geomagnetic field by electroreceptors of a slow-moving fish.

[Morphofunctional features of the catfish lateral line analyzer].

The peripheral and central portions of the catfish lateral line system were investigated by conventional light microscopical and electrophysiological methods. N. lat.