Investigation of mechanisms of synaptic transmission in ampullae of Lorenzini in the skate

The effect of magnesium ions, L-glutamate (L-GLU), and the diethyl ester of glutamic acid (DEE-GLU) on temperature and electrical sensitivity of the ampullae of Lorenzini in skates was studied by the method of perfusion of the basal membrane of electroreceptor cells and recording spike activity from single nerve fibers. Addition of 10^–4–10^–5 M L-GLU to the solution was shown to cause an increase in the spontaneous discharge frequency of receptors with low initial level of activity (8–20 spikes/sec) and a decrease in receptors with spontaneous activity of 22–42 spikes/sec. In solution with an increased magnesium ion concentration (15–50 mM) both spontaneous and evoked receptor activity was blocked, Under these conditions the addition of L-GLU to the solution caused partial recovery of spontaneous receptor activity. Reversible blocking of spontaneous and evoked receptor activity was observed in a solution containing 10^–4–10^–3 M DEE-GLU. It is suggested that L-GLU is the synaptic transmitter in the ampullae of Lorenzini of the skate.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 292–298, May–June, 1981.     

Effects of some agonists of excitatory amino acids on synaptic transmission in the skate electroreceptors (ampullae of Lorenzini)

The effects on synaptic transmission of blockers of amino acids at postsynaptic receptors were investigated by means of external perfusion of the basal membrane of electroreceptor cells in ampullae of Lorenzini and by recording of spike activity from individual nerve fibers in the skateRaja clavata: glutamic acid diethyl ester (DEE-GLU), glutamic acid dimethyl ester (DME-GLU), D--aminoadipic acid (DAA), kynurenic acid (KYN), and cis-2,3-piperidine dicarboxylic acid (PDA). The most effective blocker was found to be DEE-GLU, producing reversible blockade of postsynaptic amino acid response. It was found that DAA did not change synaptic transmission in the electroreceptors, while PDA largely affected response produced by applying L-aspartic acid (L-ASP); KYN affected response produced by L-glutamic acid (L-GLU). It is deduced that L-GLU and L-ASP are the most effective agonists at the afferent synapse of ampullae of Lorenzini and that their excitatory effect is produced by activating quisqualate receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 4, July–August, 1988, pp. 457–463.     

Influence of L-serine-O-phosphate on synaptic transmission in afferent synapses of the ampullae of Lorenzini of skates

The method of superfusion of the basal membranes of the ampullae of Lorenzini of skates was used to investigate the influence of L-serine-O-phosphate (SOP) on the background and evoked activity of afferent nerve fibers, as well as on the effects of application of agonists: exciting amino acids — L-glutamate (L-GLU), kainate (KA), quisqualte (Q), and N-methyl-D-aspartate (NMDA). It was found that SOP (threshold concentration 10^–7 M) had an inhibiting effect on the background and evoked activity of the nerve fibers; depending on the concentration it decreased the stimulatory effects of L-GLU and NMDA and did not change the responses due to application of KA and Q. The data obtained suggest that the effects of SOP observed in the ampullae of Lorenzini are associated with its interaction with NMDA-type amino acid receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 387–391, July–August, 1991.     

Effect of dalargin,a synthetic leu-enkephalin analogue on synaptic transmission in the Lorenzini ampullae of rays

Effects of dalargin, a synthetic leu-enkephalin analogue and its antagonist naloxone on synaptic transmission in afferent synapses of ray electroreceptors were investigated using an isolated preparation of Lorenzini ampullae from Black sea rays. It was shown that dalargin (10^–6–10^–10 mole liter) both decreased background activity and evoked activity of an afferent fiber in a dose-dependent manner. Naloxone (10^–5 mole/liter) also inhibited afferent impulsation and completely blocked responses of the Lorenzini ampullae to dalargin application. L-glutamate-induced excitatory responses were reduced in the presence of dalargin. It is suggested that the modulatory action of dalargin on glutamatergic synaptic transmission in the Lorenzini ampullae is exerted via specific opiate receptors.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 18–21, January–February, 1993.     

Effects of aspartic acid on skate electroreceptors

The effects of L-aspartic acid (L-ASP) on spontaneous and evoked activity in afferent nerve fibers were investigated by perfusing the basal membrane of sea skate electroreceptors (the ampullae of Lorenzini) with this substance. It was found that perfusion with physiological saline containing L-ASP exerted a primarily excitatory effect on afferent activity (threshold concentration: 10^–7 M). When synaptic transmission was blocked by magnesium ions, activity was restored in the afferent fibers if L-ASP was added to the solution and spike activity persisted for longer; this would imply the presence of desensitizing processes in the postsynaptic receptors of the ampullae. Finding would lead to the conclusion that L-ASP and L-glutamate fulfill a set of criteria for likely neurotransmitters in the ampullae of Lorenzini.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 61–67, January–February, 1987.     

Effects of quisqualate,N-methyl-D-aspartate,and some amino acid antagonists on synaptic transmission in ampullae of Lorenzini

The effects of quisqualic acid (QA), N-methyl-D-aspartate (NMDA), and a number of NMDA and non-NMDA receptor antagonists on background and induced activity in afferent nerve fibers were investigated in skates by means of bath application to the basal membrane of electroreceptors (ampullae of Lorenzini). Perfusion with physiological saline containing QA or NMDA (minimum concentrations required: 10^–8 and 10^–5 M respectively) was found to exert an excitatory effect on afferent activity. Aminoadipate and aminophosphonobutyrate had no effect on synaptic transmission, which was blocked by aminophosphonovalerate, however. Raising magnesium ion concentration (of 30 mM) led to blockade of NMDA-induced response without changing that produced by QA. Aminophosphonovalerate blocked NMDA response and partially reduced the effects of L-aspartic acid. Glutamyl glycine produced blockade of synaptic transmission. The findings obtained would point to synaptic sensitivity to the action of amino acid agonists (QA and NMDA) in the ampullae of Lorenzini.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 160–167, March–April, 1989.     

Effects of kainic acid on synaptic transmission in skate electroreceptors (ampullae of Lorenzini)

The effects of kainic acid on synaptic transmission in electroreceptors were investigated in the skate using techniques of uninterrupted superfusion of the synaptic area with a solution containing this substance and then recording the spike activity of single nerve fibers of the ampullae of Lorenzini. Kainic acid at threshold concentrations of the order of 10^–9 M effectively changed spontaneous and evoked activity of the receptors. Level of background activity served as an indication of the effects taking place. During blockage of synaptic transmission produced by magnesium ions the addition of kainic acid to the magnesium-saturated solution restored both spontaneous and evoked activity. It was deduced that the action of kainic acid on skate electroreceptors is of a primarily presynaptic nature.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 147–153, March–April, 1986.     

Reception of millimeter-band electromagnetic radiation by the ampullae of Lorenzini of skates

During recording of impulse activity from single nerve fibers of electroreceptors of the ampullae of Lorenzini of skates, we studied the responses to electromagnetic radiation (EMR) at a frequency of 37–55 GHz and an intensity of 1–100 mW/cm².Exposure of the ampullar canal pore to EMR at an intensity of 1–5 mW/cm² and a distance of 1–10 mm evoked a transient increase in the frequency of low-threshold receptor activity (current threshold was 0.04–0.2 µA). An increase in EMR intensity by more than 8–10 mW/cm² produced, together with elevation of receptor activity, an inhibition due to a rise in temperature of 1–3°C in the region exposed. The phase of increase in frequency of activity was absent in high current-threshold receptors (0.3–2.0 µA) when exposed to EMR. The receptors responded to irradiation of the ampullar canal pore at a distance of 15–20 mm by an increase in discharge frequency for 20 min. Direct irradiation of the ampullae of Lorenzini induced only inhibitory responses in receptor cells regardless of their excitability.The results obtained indicate that the sensory receptors of vertebrates are sensitive to EMR. It is concluded that the excitatory effects are due to direct reception of EMR by electroreceptors, and the inhibitory effects are related to local heating of the Lorenzini ampullar pore.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 325–329, September–October, 1993.     

Electrophysiological investigation of central neurons of the electroreceptor system of the skate

Bioelectrical responses of acoustico-lateral neurons to electrical stimulation of the ampullae of Lorenzini were investigated in acute experiments on the anesthetized Black Sea skateTrigon pastinaca. Three types of responses were found: a primary composite response, prolonged activity, and single unit activity. Excitation of the neurons corresponded to a more marked negative phase, and inhibition to a more marked positive phase of the primary response. The thresholds of the unit responses to adequate electrical stimulation were 10^–9–10^–10 A/mm² and the minimal latent period 20 msec. The spontaneous activity of some neurons clearly depended on the animal's respiration. The character of the response depended on stimulus polarity, as reflected in the appearance of on- and off-responses. A tonic type of response with features of adaptation was predominant. The dependence of some response parameters (latent period of on- and off-responses, firing rate, duration of the contrast interval, response thresholds) on those of the stimulus is analyzed. The mechanisms of these bioelectrical responses are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.1, pp.59–67, January–February, 1974.     

Effect of potassium ions on firing pattern of ampullae of Lorenzini in rays

The effect of a change in potassium ion concentration in the region of the basal membranes of the ampullae of Lorenzini of the thornback ray on spontaneous and evoked discharges of the receptors was investigated. A decrease in potassium ion concentration in the solution of perfusion with potassium-free solution led to a decrease in firing rate. Conversely, an increase in the potassium ion concentration caused an increase in discharge frequency followed by a decrease; thresholds of the receptors to the action of electrical stimuli were unchanged. When synaptic transmission was blocked by magnesium ions, an increase in the potassium ion concentration did not cause the appearance of activity in nerve fibers. If, however, activity of the nerve fibers in solution with a high magnesium ion concentration was restored with L-glutamic acid (10^–4 M), an increase in the potassium ion concentration caused an increase in firing rate. The role of potassium ions in the activity of receptors of the lateral-line system is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 493–497, July–August, 1984.     

Mechanism of perception of changes in the magnetic field by ampullae of lorenzini of elasmobranchs

The mechanisms of reception of changes in the magnetic field by electroreceptor formations were investigated in experiments on Black Sea rays in which spike activity was recorded from single nerve fibers connected with the ampullae of Lorenzini. The responses of the ampullae of Lorenzini to magnetic stimulation were shown to be due to induced electric currents creating potential gradients in the body tissues of the fish and the sea water. On the basis of differences in responses of different ampullae to magnetic stimulation, it is possible to distinguish between magnetic stimuli and other stimuli acting on the electroreceptor system. Potentiation of the receptor response to magnetic stimulation was found as the fish came closer to the "shore." The mechanisms and biological importance of reception of changes in the magnetic field by the ampullae of Lorenzini are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 1, 75–83, January–February, 1978.     

Effects of calcium and potassium channel blockers on changes in transepithelial potential and spike responses in Lorenzi ampullary electroreceptors in Raja clavata

The effects of TEA, 4-AP, Co⁺⁺, Cd⁺⁺, Cs⁺, EDTA, and verapamil on the sensory epithelium of ampullae of Lorenzini were studied inRaja clavata (Black Sea skate). During voltage clamping, transepithelial application of TEA to the basal surface caused oscillations in transepithelial potentials in response to presentation of an excitatory stimulus, which had been suppressed by Co⁺⁺, Cd⁺⁺, and EDTA. Application of Cs⁺ was followed by complete or partial suppression of spike response adaptation. When applied to the apical epithelial surface, TEA produced an increase in spike response to stimulation and highly accelerated adaption. No substantial changes took place after apical application of Co⁺⁺, Cd⁺⁺, and verapamil. The mechanisms of these phenomena are discussed.Deceased.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 652–659, September–October, 1985.     

Cutaneous mechanism of electroreceptor temperature sensitivity of the ampullae of Lorenzini

The potential difference on the receptor epithelium of the ampullae of Lorenzini and on the skin and also spike discharges of single electroreceptor nerve fibers in response to temperature stimulation of the region of the pores of the ampullae were studied in the Black Sea skateRaja clavata. Heating the skin in the region of the pore led to the appearance of a positive potential on the skin and on the epithelium of the ampulla, and to inhibition of spike activity. The time course of the change in potential reflected the course of change of temperature; the temperature coefficient was 100–150 µV/°C. Cooling the skin was accompanied by a negative deviation of potential on the skin and in the ampullary canal and by excitation of spike activity. During cooling the temperature coefficient was 30–50 µV/°C. It is concluded that spike activity of electroreceptors reflects changes in potential on the skin due to changes in temperature. The mechanism and biological significance of the phenomena discovered are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 307–314, May–June, 1981.     

Investigation of the mechanism of temperature sensitivity of the electroreceptors of ampullae of lorenzini

In experiments on Black Sea skates (Raja clavata), the potential of the receptor epithelium of the ampullae of Lorenzini and spike activity of single nerve fibers connected to them were investigated during electrical and temperature stimulation. Usually the potential within the canal was between 0 and –2 mV, and the input resistance of the ampulla 250–400 k. Heating of the region of the receptor epithelium was accompanied by a negative wave of potential, an increase in input resistance, and inhibition of spike activity. With worsening of the animal's condition the transepithelial potential became positive (up to +10 mV) but the input resistance of the ampulla during stimulation with a positive current was nonlinear in some cases: a regenerative spike of positive polarity appeared in the channel. During heating, the spike response was sometimes reversed in sign. It is suggested that fluctuations of the transepithelial potential and spike responses to temperature stimulation reflect changes in the potential difference on the basal membrane of the receptor cells, which is described by a relationship of the Nernst's or Goldman's equation type.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov, Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Pacific Institute of Oceanology, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 67–74, January–February, 1980.     

Changes in transepithelial potential and spike responses of ampullae of Lorenzini of the skate to temperature stimulation

Response of the sensory epithelium of single ampullae of Lorenzini and spike responses of nerve fibers connected to them to temperature stimulation of the region of the sensory epithelium were studied in experiments on Black Sea skatesRaja clavata. Electrically isolated ampullae with input resistance R=500–800 k, to which an external load (a controllable resistance R_ext) could be connected through a feedback circuit, were investigated. Heating the ampulla was accompanied by the appearance of a negative potential in the canal, and other conditions being the same, its magnitude was an almost linear function of the resultant inward resistance of the preparation [R_in=(R_a·R_ext)/(R_a+R_ext)]. The character and intensity of the spike response of the nerve fiber also was determined by the magnitude of R_in. With a resistance of more than 400–500 k, quickening of spike activity occurred in response to heating, and the degree of quickening increased with an increase in R_in. With a smaller value of R_in, the discharge was inhibited, and the inhibition strengthened as the resistance decreased. The presence of two sources of potential, evoked by a change of temperature and giving rise to opposite spike responses, is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR. Leningrad I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 11–18, January–February, 1982.     

Responses of the ampullae of Lorenzini in a uniform electric field

A linear relationship was established by analysis of discharges from electroreceptors of the ampullae of Lorenzini in a uniform electric field between the potential difference on a single ampulla and the relative change in the spike response of a single fiber. This relationship can serve as the basis for a model of activity of ampullary groups considered as functional units of the electroreceptor system.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 158–166, March–April, 1979.     

Neuropharmacological analysis of synaptic transmission in the Lorenzinian ampulla of the skate Raja clavata

Summary Dissected ampullae of Lorenzini of the skate (Raja clavata) were studied with the aim of determining the synaptic transmitter between electroreceptor cell and afferent fibre. Resting activity and stimulus-evoked activity in response to electrical pulses were recorded in single afferent units at constant perfusion with normal and test solutions containing different putative neurotransmitters. Presynaptic transmitter release was blocked by Mg²⁺ (up to 50 mM) to investigate the effects of the test substances upon the postsynaptic membrane. l-Glutamate (l-GLU) and l-aspartate (l-ASP), both at concentrations between 10^-7 and 10^-3 M, enlarged strongly resting and stimulus-evoked discharge frequency in the afferent fibre. If transmission was blocked by high Mg²⁺, resting discharge frequency could be restored by l-GLU or l-ASP. The glutamate agonists quisqualate (10^-8–10⁵ M) and N-methyl-D-aspartate (10^-5–10^-3 M) enlarged spontaneous activity in the afferent fiber. The same was found for kainic acid (10^-9–10^-5 M). Taurine at concentrations between 10^-5 and 10^-3 M caused a concentration-dependent decrease in afferent activity. The same was found for gammaaminobutyric acid (GABA; 10^-5–10^-4 M), and for the catecholamines adrenaline and noradrenaline, both in concentrations between 10^-5 and 10^-3 M. Serotonine (10^-5–10^-3 M) and dopamine (10^-5-10^-3 M) had no effect on resting or evoked activity in the Lorenzinian ampulla afferents. Acetylcholine (ACh; 10^-4 M) enlarged discharge frequency in those units with initial rates lower than 22–25 Hz, but diminished discharge frequency in fibres with initial activity higher than 25 Hz. When synaptic transmission was blocked by high Mg²⁺ solution, perfusion with additional ACh did not restore resting activity in the afferent fibre. The results suggest that the most probable transmitter in the afferent synapse of the ampullae of Lorenzini is l-GLU or l-ASP, or a substance of similar nature.Abbreviations ACh acetylcholine - GABA gamma aminobutyric acid - KA kainic acid - l-ASP l-aspartate - l-GLU l-glutamate - NMDA N-methyl-D-aspartate - Q quisqualate - n.s. normal solution     

Electrophysiological investigation of the properties of the electroreceptors (ampullae of Lorenzini) in Black Sea rays

Responses of electroreceptors (ampullae of Lorenzini) in Black Sea rays to electrical stimuli were recorded in vivo as spike activity of single nerve fibers. Depending on their functional properties the fibers could be divided into silent, those with regular activity (10–15 spikes/sec) and those with grouped activity. Electrical stimuli evoked a tonic response with a varied degree of adaptation in the nerve fibers. The threshold currents were between 10^?10 and 10^?11 A/mm². The minimal latent period of the on-responses to pulses of current of maximal intensity was 15–40 msec, whereas that of the off-responses was 15–200 msec. The effect of intensity, duration, and polarity of the stimuli on the responses of the receptors and the adaptation of the electroreceptors during application of a steady current were investigated. The properties of the ampullae of Lorenzini were compared with those of other types of electroreceptors.     

Synaptic effects of nicotinic and muscarinic agonists in sympathetic ganglia of the frog

Superfusion of the isolated sympathetic ganglia of the frog with nicotinic agonists (suberyldicholine, tetramethylamonium, and dimethylphenylpiperazinium), as well as acetylcholine in the presence of atropine led to a brief depolarization of the neurons and blockade of synaptic transmission. The muscarinic agonists methylfurmethide (MFM) and methyldilvasen, cis^–, L(+), as well as acetylcholine elicited a stable depolarization which is not accompanied by disturbance in transmission. Oxotremorine at a concentration of 1·10^–5 M did not lead to the depolarization of the post-synaptic membrane, but at a concentration of 1·10^–6 M decreased the quantal EPSP content twofold, which indicates that the presynaptic receptors belong to the M₂ subtype. Inhibition of acetylcholinesterase significantly intensified the postsynaptic effect of MFM: a shift of the concentration-effect curve took place toward the side of lower MFM concentrations. It was shown that the post-synaptic muscarinic receptors of the ganglionic neurons possess varied sensitivity to the enantiomers of methyldilvasen and, consequently, are stereospecific. The identified functional properties of the cholinoreceptors of the ganglionic neurons explain the set of changes in synaptic transmission under conditions of the prolonged presence of a mediator in the synaptic cleft.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 227–234, March–April, 1988.     

Voltage-dependence of cobalt-induced blockade of synaptic transmission between photoreceptors and horizontal retinal cells

Synaptic transmission between photoreceptors and horizontal cells in the turtle retina blocked by Co²⁺ ions can be restored by passing constant radial current through the retina which depolarizes presynaptic receptor terminals. This finding is unassociated with current action on horizontal cells themselves, since polarization of these cells via an intracellular microelectrode did not restore response to light. The unblocking effect of depolarization at the receptor synaptic endings consists of two components: the opening of additional calcium channels not blocked by Co²⁺ at the presynaptic membrane and cobalt-induced voltage-dependent blockade of clacium channels. The latter may explain the paradoxical phenomenon of increased response to the action of moderate light in horizontal cells during cobalt-induced partial blockade of synaptic transmission.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 374–383, May–June, 1988.