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.     

Effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata

Summary The spectral sensitivity of the ocellus in the cucumber looper moth, Anadevidia peponis, was investigated by recording electroretinograms (ERGs). The peak sensitivities were observed at 340 nm in the ultraviolet and at 520–540 nm in the green. Selective spectral adaptation revealed the existence of at least two receptor types in the ocellar retina. The ratio of green to ultraviolet sensitivities for an ocellus whose ocellar nerve was cut was higher than that for an intact ocellus. It is suggested that efferent signals which control the spectral sensitivity of the ocellus are present in the ocellar nerve.Abbreviations ERG electroretinogram - GR/UV green to ultraviolet sensitivities - ON ocellar nerve     

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.     

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

1. Effects of kainic acid (KA) on resting and evoked activities of the ampullary electroreceptor were studied in marine skates (Raja clavata). 2. Perfusion of the basal membrane with 10(-6)-10(-9) M KA produced significant and reversible changes in impulse activity depending on initial firing rate. 3. When synaptic transmission was blocked by perfusion with elevated Mg2+, the resting and evoked activities were restored if KA was added. 4. The results are consistent with the view that KA is a potent excitant of the ampullae receptors and its effects appear to be presynaptic.     

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.     

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.     

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.     

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.     

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     

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.     

A morphological analysis of the ampullae of Lorenzini in selected skates (Pisces,Rajoidei)

A comparison of the ampullae of Lorenzini among 40 species of skates (Rajoidei) demonstrates a close relationship between inferred electroreceptive capabilities and feeding mechanisms. Three general lines of morphological modifications are noted. (1) Whereas the majority of ampullary pores are located on the ventral surface of the dorsoventrally flattened body, the relative proportion of ventral pores is significantly lower on species inhabiting aphotic waters. (2) The ventral pores on more piscivorous species are distributed over a larger portion of body surface than they are on those species that feed primarily on invertebrates. Ventral pores in this latter group are more noticeably concentrated around the mouth and their densities on the adult are inversely related to the overall mobility of preferred prey species. (3) The size of each ampulla and the number of alveoli associated with it are directly related to the habitat depth occupied by each species. Shallow-water species have smaller ampullae with fewer alveoli than deeper-dwelling (> 1,000 m) species. The general distribution of ampullary pores on deep dwelling rajoids appears to compensate for reduced visual input, whereas their relative densities are a measure of the system's resolution and reflect major differences in feeding strategies. The increased ampullary size and complexity observed in deep-sea rajoids provides mechanisms to increase both the sensitivity and signal-to-noise ratios.     

Effects of cadmium ions on synaptic transmission in the frog tectum

The effects of cadmium ions on synaptic transmission in the frog tectum were investigated in acute experiments using quantal EEG recording techniques (readings of extracellular monosynaptic potential induced by activating the synapses of a single axon) [1]. Superfusion of the tectum by 10–200 µM CdCl₂ reversibly inhibits EEG quanta, reduces their duration (measured at 50% amplitude level) and increases synaptic delay. The results of this study confirm the concept formed from in vitro experiments of votage-dependent calcium channels as one of the likely Cd²⁺ action sites at central synapses. It is concluded that cadmium-induced industrial pollution may also pose a threat in the form of damaging action on the central nervous system.Medical Institute, Ministry of Public Health of the Lithuanian SSR, Kaunas. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 756–765, November–December, 1989.