Morphological changes in axodendritic synapses of the leech during blocking of conduction in medium with reduced ionic concentration

Reactive changes were found by supravital staining with methylene blue in the synaptic system of the neuropil ofHirudo officinalis. They consist of marked bead-like deformation of the presynaptic portions, enlargement of the terminal structures, initial decolarization of the isthmuses between the boutons, and the clearer demonstration of the neurofibrils in the expanded postsynaptic dendrites. In a specially treated preparation of clearly identifiable axodendritic synapses of the leech it was shown that these changes reach a considerable magnitude when electrical activity in the ventral chain is blocked. This fact suggests that, together with other factors, they participate in the development of the conduction block.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 613–618, November–December, 1977.     

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.     

Electrical transmission between nonsymmetrical neurons in the leech ganglion

The extent of the electrical transmission (ET) between different nonsymmetrical neurons in the segmental ganglion of the abdominal nerve chain of the leechHirudo medicinalis L. was investigated. ET was demonstrated by simultaneous recording of the intracellular potentials in two neurons when bursts of a polarizing current were passed alternately into each of them. At least 16 different pairs of nonsymmetrical identifiable neurons with ET which, as a rule, was symmetrical with a coefficient of attenuation of the order of 10 in the direction of greater effectiveness, were found. In different pairs of nonsymmetrical identifiable neurons, the ET of hyperpolarizing currents as a rule is more effective from neurons with a higher frequency of background activity. The presence of ET was also shown between many nonsymmetrical unidentifiable neurons of the ganglion. The assymetrical ET in some of the combinations of neurons investigated did not have rectifying properties. The direction of the ET was retained in them for any polarity of the polarizing current. In some experiments hyperpolarization of one of the neurons of a pair evoked depolarization and an increase in the frequency of the impulse activity of the other, while depolarization had the opposite effect ("negative" ET). It was concluded that the broad extent of the ET between nonsymmetrical neurons indicates its important role in the integrating activity of the central nervous system of the leech.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 550–556, September–October, 1971.     

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.     

Action of calcium on the somatic membrane of mollusk giant neurons

Early membrane currents of the isolated neuron soma of the mollusksHelix pomatia,Limnaea stagnalis, andPlanorbis corneus in normal and sodium-free solutions differing in their calcium ion concentration were investigated by the voltage clamp method. The early inward current was shown to continue when the sodium ions in the external solution were replaced by an equivalent number of calcium ions and to be increased with an increase in the concentration of those ions in all neurons of these mollusks investigated. A change in the calcium concentration in the external solution shifted the inactivation curves and also the curves of conductance for the inward current along the potential axis. It is concluded that a system of calcium channels exists in the somatic membrane of neurons in these species of mollusks.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 621–627, November–December, 1973.     

Effects of applying oxytocin to Helix pomatia neurons. II. Hyperpolarization

The ionic mechanisms of hyperpolarization produced by applying oxytocin (OT) were investigated at the membrane of identifiedHelix pomatia neurons. Two types of neuron were known to exist, in one of which hyperpolarization is produced by a reduction in chloride ions at the membrane and a rise in membrane permeability to potassium ions in the other. In the first of these, response to OT had a reversal potential of –40 mV and decreased when furosemide and tolbutamide were added to the external medium. In the second case, the potential of the reversal of the response to OT was –70 mV. Upon doubling of potassium ion concentration in the external solution it was shifted towards depolarization by 15 mV. It is sugested thatHelix pomatia neurons have different types of OT receptors, some of which, when activated, manifest reduced chloride permeability at the membrane (probably through the cell cyclase system) with a rise in potassium permeability at the membrane in others.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 659–666, September–October, 1988.     

Effects of glutamic acid diethylester on synaptic transmission in the skate ampullae of Lorenzini

The effects on synaptic transmission of glutamic acid diethylester (GDEE), a glutamate receptor blocker, were investigated by recording spike activity from single nerve fibers in the electroreceptor cells of the skate (Raja clavata) ampullae of Lorenzini. It was found that adding GDEE to the bathing medium led to a concentration-dependent reduction in or complete blockade of background and evoked receptor activity; 10^–6 M GDEE was the minimum effective concentration. It was also shown that GDEE reversibly blocked postsynaptic response produced by excitatory amino acids: L-glutamate (L-GLU) and L-asparate (L-ASP). Findings suggest the involvement of L-GLU or a related substance in synaptic transmission in the ampullae of Lorenzini.I. P. Pavlov Institute of Physiology of the Academy of Science of the USSR, Leningrad, USSR. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 323–327, May–June, 1987.     

Effect of theophylline on electrical activity of bursting type in an identified Helix pomatia neuron

The effect of theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, on electrical activity of bursting neuron RPa1 ofHelix pomatia was investigated. In a concentration of 1 mM theophylline, when added to the external solution, increases the frequency and number of action potentials in the burst and also the duration of the inter-burst interval and the amplitude of membrane potential waves. In concentrations of 2.5 and 5.0 mM theophylline leads to reversible inhibition of bursting activity. During rinsing this activity rises to a higher level and then returns to the original value. The action of theophylline develops and disappears (as a result of rinsing) in the course of 1–5 min, depending on concentration of the inhibitor. It is suggested that electrical activity of the molluscan bursting neuron is controlled through the cyclic nucleotide system.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 75–79, January–February, 1981.     

The slow negative wave of the evoked potential of the frog midbrain tectum

A surface-negative slow wave (SW) with a latent period of 50–60 ms, an amplitude of up to 3 mV, and a duration of 0.5–1.5 sec follows the postsynaptic components in the potential of the midbrain tectum (MBT) of a curarized frog (Rana temporaria L.) evoked by electrical stimulation of the optic nerve. The SW develops as a result of the arrival of a synchronous afferent volley along amyelinic fibers; it is generated as a result of depolarization of radially oriented cellular elements; the periventricularly located parts of these structures serve as the source of the current. In the case of rhythmical stimulation, the SW is summed to a value exceeding 10 mV, while at the beginning of stimulation with a frequency of 10–40/sec, the SW is facilitated. After the injection of picrotoxin, selective sensitivity of the SW to this substance was not found. An SW also develops from direct stimulation of the MBT. Comparison of the results of recording neuronal activity shows that the SW is connected with direct afferent inhibition. It is assumed that the SW is generated by elements of the ependymoglia.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 145–153, March–April, 1971.     

Electron-microscopic analysis of adrenergic nerve endings in the cat caudal mesenteric ganglion

The ultrastructure of nerve endings of the cat caudal mesenteric ganglion was studied after fixation of the material with 4% lithium permanganate solution by Richardson's method in the modification of Hökfelt et al. [12]. This fixation method was shown to permit the demonstration of numerous adrenergic as well as cholinergic nerve endings. Four types of adrenergic organelles were distinguished in neurons of the ganglion: small and large granular vesicles 30–50 and 70–90 nm in diameter, respectively, a tubular reticulum with electron-dense contents, and small granular vesicles 15–20 nm in diameter. The localization of the adrenergic endings and their relations with other processes and cells of the caudal mesenteric ganglion were studied in detail. The problem of the origin and physiological role of adrenergic nerve endings in this ganglion is discussed.Institute of Physiology, Academy of Sciences of the Belorussian SSR, Minsk. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 86–92, January–February, 1980.     

Neural control of heartbeat in the pteropod mollusk Clione limacina

The heart of the pteropod molluskClione limacina is innervated by the median nerve arising from the left abdominal ganglion. Five neurons sending axons to the heart have been identified in theClione central nervous system with retrograde cobalt or Lucifer yellow staining. Neuron H1 located in the left pedal ganglion produced an excitatory effect on heart beat. Stimulation of three neurons, H2–H4, situated in a compact group in the medial region of the left abdominal ganglion, led to inhibition of cardiac contraction, while H5, located in the caudal region of the left abdominal ganglion, did not affect heart beat. The activity of efferent cardiac neurons (ECN) was found to be related to the operation of the locomotor rhythm generator. Spontaneous or reflex depression of the latter was found to inhibit neuron H1 and activate units H2–H4. The behavior of these ECN accounts for the positive correlation between heart operation and locomotor activity inClione limacina.Institute of Research on Information Transmission, Academy of Sciences of the USSR, Moscow, M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 185–192, March–April, 1989.     

Effects of applying oxytocin to Helix pomatia neurons. I. Depolarization

Inward current produced by applying oxytocin (OT) to the neuronal soma (OT_I) current) under conditions of voltage-clamping at the cell membrane was investigated inHelix pomatia. Replacing sodium with Tris ions in the external medium produced a considerable decline in OT_I current. A reduction in the external concentration of chlorine ions by replacement with HEPES ions induced an increase in OT_I current and a shift in its current-voltage relationship towards depolarization values. The presence of furosemide in the external solution reversibly inhibited OT_I current. This current likewise declined reversibly following external application of imidazole and tolbutamide but was increased by theophylline action. It was inferred that OT receptors are present on the surface membrane of someHelix neurons which, when activated, lead to increased chlorine permeability — a process apparently mediated via the cyclic nucleotide system.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 652–659, September–October, 1988.     

Restoration of retino-tectal connections in frogs during regeneration of the optic nerve

At various times after unilateral division of the optic nerve in the frogRana temporaria L. evoked potentials in response to electrical stimulation of the optic nerve were investigated in a segment distal to the site of operation, spike activity was recorded from endings of regenerating and intertectal axons when stimuli of different shapes were placed in the field of vision, and the distribution of axonal bulbs of growth by depth in the tectum mesencephal was studied electron-microscopically. During regeneration of the axons the responses of the retinal ganglionic cells to visual stimuli retained most of their individual features. Myelinated axons of the retinal ganglionic cells regenerate first (starting on the 21st day after operation). Myelination of these fibers lags significantly behind their growth and is complete more than 100 days after the operation. Unmyelinated axons of the retinal ganglionic cells grow up toward the tectum mesencephali after myelinated axons (80 or more days after the operation). Axonal bulbs of growth in the initial periods after the operation are located close to the pial surface and the level of spread of the myelinated axons of the retinal ganglionic cells differs significantly from their normal level of localization. Intertectal connections persist after division of the nerve and are activated by visual stimuli during regeneration of the axons of the retinal ganglionic cells. Connections were found mainly between intertectal fibers terminating superficially and retinal ganglionic cells belonging to class 1 and 2 detectors. Axons of the retinal ganglionic cells grow up toward the caudal region of the tectum mesencephali later than toward the rostral region.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 611–620, November–December, 1973.     

Similarities and differences in the structure of segmentally homologous neurons that control the hearts in the leech,Hirudo medicinalis

Summary The neural circuit that controls the hearts in the leech comprises an ensemble of synaptically interconnected cardiac motor neurons (HE cells) and cardiac interneurons (HN cells). Both the HE cells and the HN cells constitute segmentally homologous sets. We have investigated the structure of these neurons by iontophoretic injection of Lucifer Yellow dye.Bilateral pairs of HE cells have been identified in segmental ganglia 3–19 of the nerve cord. Their structure was found to be nearly identical from ganglion to ganglion and from animal to animal.Bilateral pairs of HN cells have been identified in segmental ganglia 1–7 of the nerve cord. Their dendritic structure was found to vary from ganglion to ganglion. These segmental differences among HN cells were observed consistently from animal to animal. Some of the segmental differences in HN cell structure correlate with previously described physiological differences.     

Effects of extracellular potassium ions on outward potassium current dependent on extracellular calcium ions

Changes in outward potassium current occurring in response to changes in the concentration of potassium ions in the extracellular medium were investigated in unidentified neurons isolated fromHelix pomatia using an intracellular perfusion technique. It was found that introducing potassium ions (5–10 mM) into the extracellular solution produces a reversible increase in the component of outward potassium current which is dependent on extracellular calcium ions. Increased amplitude of this component occurs as a result of attenuated inactivation of the current under the action of extracellular potassium.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 351–356, May–June, 1987.     

Glucose isomerase activity of streptomyces kanamyceticus

Summary Streptomyces kanamyceticus produces a significant level of intracellular glucose isomerase when grown in submerged culture. The optimum temperature for enzyme activity is 90°C, but the optimum pH is changed by the kinds of buffer solution used. The activity is higher at pH 7.0–9.5. Treatment of cells with cetyl trimethyl ammonium bromide extracts almost the same amount of the enzyme as ultrasonic treatment. The selection of the method of treatment for enzyme extraction depends, however, on the nature of cell growth in synthetic or complex medium.     

Chemical modification of lipase with ferromagnetic modifier — A ferromagnetic-modified lipase

Summary A ferromagnetic modifier was prepared by reacting ferrous(Fe²⁺)- and ferric(Fe³⁺)-ions with polyethylene glycol having two carboxyl groups (MW:2000) at pH 8.0–8.5. Lipase fromPseudomonas fragi 22–39B was coupled with the modifier using water-soluble carbodiimide. The modified lipase, which was dispersed into buffered solutions in the size range of 30–70 nm, exerted the hydrolytic activity of 8.0 U/mg. In a magnetic field of 250 Oe, the ferromagnetic-modified lipase was readily recovered from the colloidal solution.     

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.     

Rhythmic activity evoked by adequate stimulation in the fish retina

The distribution of evoked rhythmic responses on the surface and in the depths of the retina of the carp (Cyprinus carpio) and tench (Tinca tinca) and the dependence of the amplitude — frequency characteristics of the response on stimulus intensity and duration were investigated by recording the local electroretinogram and unit activity of the ganglion cells. Rhythmic on- and off-responses to light differed in various characteristics, including their distribution between the cellular and synaptic layers of the retina. The frequency, amplitude, and number of waves in the response were found to depend on the parameters of the stimulus. On-, off-, and on — off-ganglion cells were represented in the records. Their spike discharge usually corresponded to a phase angle of the negative half-wave of the rhythmic response of close to /2. The results of experiments in which conduction along the optic nerve was blocked by cold showed that the system of generation of the rhythmic response in the retina is under the tonic influence of the centers.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 61–68, January–February, 1977.     

Mechanism of the exciting action of noradrenalin and adrenalin on the smooth muscle cells of the portal vein

The ionic mechanism of the exciting action of catecholamines — nonadrenalin and adrenalin — on the muscle cells of the portal vein of the rat was investigated by the method of a double "sucrose bridge." To determine the role of various ions in the action of catecholamines, they were removed from Krebs solution and replaced by other ions. In muscle cells kept in sodium-free Krebs solution, just as under normal conditions, the catecholamines induced depolarization of the membrane, an increase in the spontaneous electrical activity, an increase in the excitability, and a decrease in the amplitude of the electrotonic potentials (ETP), i.e., the resistance of the membrane. The exciting action of catecholamines on muscle cells also did not cease after the removal of Ca⁺⁺ from solution. This action of them was not manifested only in the case when Na⁺ and Ca⁺⁺ were removed simultaneously from the surrounding solution. Thus, the exciting action of noradrenalin and adrenalin on muscle cells of the portal vein is due to a decrease in the permeability of the cell membrane for Na⁺ and Ca⁺⁺ in a definite quantitative ratio.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 643–653, November–December, 1970.