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.     

Changes in distribution of synaptic vesicles in endings of cones during electrical stimulation of the retina

Conditions (hypoxia) were chosen under which, judging from the reduction in the responses of the horizontal cells to electrical stimulation of the retina, mediator is exhausted in the presynaptic endings of the photoreceptors. Under these circumstances a number of "small" synaptic vesicles were shown to be reduced in those parts of the cones which are in direct contact with presynaptic membranes. No significant changes were found in the total number of "small" vesicles in the cone endings.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 620–623, November–December, 1976.     

Investigation of the nature of electrical responses of horizontal cells of the fish retina

On the basis of the syncytial structure of the layer of horizontal cells of the fish retina, a method is developed which effectively shifts the membrane potential of cells by means of an electrical current. It is shown that the response of L-type horizontal cells to light and electrical stimulation of the retina is reversed when the membrane of the horizontal cells is depolarized by a direct current. The equilibrium potential of the cells was near the zero level. Consequently, the depolarization response of the horizontal cells to disconnection of the light and to electrical stimulation of the retina is an excitatory postsynaptic potential, whereas hyperpolarization of the horizontal cells to light is a decrease of this potential. It is shown that the membrane of fish horizontal cells have pronounced nonlinear properties: in the case of strong depolarization and especially in the case of hyperpolarization its impedance drops markedly. The latter probably occurs due to an increase of the permeability of the nonsynaptic membrane of the horizintal cells for K⁺. This can also explain the decrease of membrane impedance during the hyperpolarization response of the horizontal cells to bright light. The available data indicate the presence of regenerative properties of the membrane of horizontal cells.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 89–98, January–February, 1971.     

Electrical properties of subsynaptic and nonsynaptic membranes of horizontal cells of the turtle retina

Horizontal cells of the L-type in the turtle retina were polarized by passing a steady current through extracellular electrodes. In this way controlled changes in membrane potential can be effectively produced in the region of the cell body. The hyperpolarization response of the horizontal cell to light is reversed on depolarization of the cell membrane to about the zero level. Consequently, the response of the horizontal cell to light is the result of a decrease in the EPSP, the magnitude of which remains constant in darkness. The resistance of the cell membrane depends on the membrane potential. Hyperpolarization of horizontal cells produced by bright light or by passage of a steady current was accompanied by a decrease in their membrane resistance. This nonlinearity evidently depends on the properties of the nonsynaptic membrane of the horizontal cells, whose resistance falls considerably on hyperpolarization. The results are qualitatively similar to those demonstrated previously [10] in an investigation of the horizontal cells of the fish retina.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 423–431, July–August, 1973.     

Membrane potential clamping in horizontal cells of the fish retina

The membrane potential of horizontal cells of the retina was clamped by uniform polarization of the layer of these cells by a current passed through extracellular electrodes. The volt-ampere characteristic curve of the synaptic membrane of the horizontal cells in some cases had segments with negative slope. With a sharp change in the level of voltage clamping the time taken for the resistance of the membrane to change was under 20 msec. Comparison of responses to photic stimulation recorded with and without voltage clamping showed that participation of the nonsynaptic membrane in the generation of responses to photic stimulation can affect their shape substantially.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 402–407, July–August, 1977.     

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.     

Effect of polarization of horizontal cells of the pike retina on spread of their electrical potentials

The spread of electrical responses over the layer of horizontal cells of the pike retina was investigated at different levels of their membrane potential varied by application of a steady current. Depolarization of the membrane, accompanied by an increase in its resistance, led to an increase in its time constant and length constant, so that electrical waves spread further over the layer of horizontal cells. The effect of polarization was thus due to the nonlinear membrane properties of the horizontal cells, i.e., to the increase in their resistance on depolarization and its decrease on hyperpolarization. In some cases this nonlinearlity was manifested as a special type of regeneration: the same strength of steady current crossing the membrane of the horizontal cells corresponded to two stable levels of the membrane potential. The role of various factors (changes in resistance of the extrasynaptic and subsynaptic membranes of the horizontal cells, the presynaptic effect of the current) determining the spread of the potentials over the horizontal cells under natural conditions during photic stimulation is discussed.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 1, pp- 90–96, January–February, 1972.     

On the role of horizontal cells in the mechanism of retinal adaptation

We recorded by intracellular means responses of horizontal cells of the turtle retina to light increase and decrease of different values against the starting adapting level. In measuring these responses, curves reflecting the dependence of membrane potential deflection on light intensity (amplitude characteristics — ACh) were plotted. It is demonstrated that the ACh of transitional processes (on- and off-peaks) is considerably steeper than ACh of the plateau of the potential, but embraces a much smaller range of light intensities (slightly more than 1 log. un.). During a change in intensity of the adapting background (up to 3 log. un.), the ACh of transitional processes shifts along the scale of light intensities in such a way that its steep part remains in the zone of adapting light. We followed the dynamics in time of ACh shift after the transition from one adapting brightness to another. The ACh of total impulse response was plotted for ganglionic cells of the turtle at different intensities of adapting light. Comparison of these curves with the ACh of horizontal cells shows that its peripheral components are responsible for adaptive shifts of ACh of the visual system and that horizontal cells play an important role in the mechanism of adaptation. It is hypothesized that adaptive ACh shifts are the consequence of positive feedback between the horizontal cells and receptors.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 210–218, September–October, 1969.     

Ion exchange in the horizontal cells of the retina

Experimental data indicate that the membrane potential of L-type horizontal cells of the retina to bright light (i.e., when synaptic inputs are completely closed) is close to the potassium equilibrium potential. From this observation the intracellular concentration of K⁺ and Na⁺ was estimated. The latter was found to be relatively high (tens of millimoles/liter), i.e., comparable with the intracellular K⁺ concentration. This result, coupled with data on closeness of the equilibrium potential of the photic response to zero, is evidence that besides sodium conductance, the potassium conductance of the subsynaptic membrane also participates in generation of the photic response by these cells. The steady-state sodium and potassium synaptic currents was shown to be relatively small and to vary only a little over the whole working range of potentials (from –72 to –16 mV), due to the nonlinear properties of the nonsynaptic cell membrane.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 3–10, January–February, 1982.     

Measurement of the latent period of the response of the turtle horizontal retinal cell to electrical stimulation

We have measured the latent period of the depolarization reaction occurring in horizontal cells in response to short bursts of current sent through the retina (anode on sclera, cathode in vitreous). The latent period varied in different experiments from 3 to 7 msec. It is thought that the current acts directly on the presynaptic membrane of the receptors, and that the measured value of the latent period comprises the time of synaptic delay in the transmission of the signal from the receptors to the horizontal cells. The value of the latent period is close to the time interval between the onset of the distal and proximal subcomponents of P_III, as measured by Murakami et al [7, 8], an interval which probably represents time between the onset of the receptor potential and the development of the electrical response of the cells of the inner nuclear layer.Institute of Problems of Transmission of Information, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 87–90, January–February, 1970.     

Changes produced in neuronal excitability by subthreshold depolarization as a possible mechanism of interval selective relationships within the central nervous system

A neuronal process was identified inLymnaea stagnalis nerve cells which may be viewed as one of the mechanisms underlying the interval selectivity previously described in research into the functional relationships between mammalian brain cells. This process takes the form of regularly-occurring changes in excitability resulting in a high probability (of 0.6–1) of neuronal spike response to what had previously been subthreshold depolarizing current pulses following similar subthreshold (conditioning) pulses at intervals specific to each individual neuron. It was found that the cycle of change in neuronal excitability following threshold depolarization did not arise from temporal summation of electrotonic local or postsynaptic neuronal potentials; it was an endogenous (cytoplasmic) process insensitive to transmitter (acetylcholine) application but altering irreversibly under the effects of bombesin, one of the modulator peptides.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad; Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologya, Vol. 21, No. 3, pp. 291–299, May–June, 1989.     

Model feedback mechanism between horizontal cells and photoreceptors of the vertebrate retina

A model with nonlinearity of the photoreceptor presynaptic membrane as its important distinguishing feature was created on the basis of the hypothesis that feedback between the horizontal cells and photoreceptors is effected by a current generated by the subsynaptic membrane of the horizontal cells and leaking partly into the photoreceptors. Measurements with the model also reproduced experimental observations such as depolarization of the cone during hyperpolarization of the horizontal cell in response to the showing of a ring of light or passage of an electric current, and also certain special features of the current-voltage curves of the cones.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 86–94, January–February, 1977.     

Ionic mechanism for the generation of horizontal cell potentials in isolated axolotl retina

The ionic mechanism of horizontal cell potentials was investigated in the isolated retina of the axolotl Ambystoma mexicanum. The membrane potentials of both receptors and horizontal cells were recorded intracellularly while the ionic composition of the medium flowing over the receptor side of the retina was changed. The membrane potential of the horizontal cell is highly depender side of the retina was changed. The membrane potential of the horizontal cell is highly dependent on the extracellular concentration of sodium. When the external ion concentration of either chloride or potassium was changed independently of the other, there were shifts in the membrane potential of the horizontal cell which could not be explained by changes in the equilibrium potential of these ions. If the external concentrations of both potassium and chloride ions were varied so that the product of their external concentrations did not change, the shift in the membrane potential of the horizontal cell was in the direction predicted by the Nernst equation. The results are consistent with the suggestion that in the dark the receptors release a synaptic transmitter which increases primarily the sodium conductance of the horizontal cell postsynaptic membrane.     

Local changes of resistance in the retinal horizontal cell evoked by changes in membrane potential

A steady current (10·10^–10–6·10^–9 A) was passed by means of a bridge circuit through a recording microelectrode inserted into a horizontal cell of the turtle retina. Illumination of the retina caused an increase in the resistance of the microelectrode circuit (by 10–80 M), causing a change in the shape of the recorded response of the horizontal cell to light. The change in resistance was shown to take place, not on the cell membrane itself, but inside the cell close to the microelectrode tip. The effect described can be reproduced by passing a current through one barrel of a double-barreled microelectrode alongside the recording barrel, but the strength required for this current was greater than that passed through the recording barrel. If the membrane potential of the horizontal cell was made equal to the equilibrium potential (by means of a steady current passed through extracellular electrodes) the hyperpolarization response to light and the effect of the increase in resistance of the microelectrode circuit disappeared simultaneously. On the other hand, artificial hyperpolarization of the cell membrane caused an increase, but depolarization caused a decrease in the resistance of the microelectrode circuit. It is postulated that the observed effect is due to blocking of the microelectrode tip by an intracellular structure whose resistance varies with a change in membrane potential.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol.5, No.4, pp.432–441, July–August, 1973.     

Changes in functional characteristics of the compound eye of bees caused by mutations disturbing tryptophan metabolism

The compound eye of worker honeybees with an inborn disturbance of intermediate metabolism of tryptophan — the snow (s) and laranja (la) mutations — has increased sensitivity to light, at least 100 times higher than normal in snow and at least 10 times higher in laranja. The maxima of the spectral sensitivity curves for the whole eye in snow are shifted into the 530 nm region and in laranja to 550 nm (comparedwith 545 nm for the wild type). The electroretinograms of s andla homozygotes are unusual in form on account of the presence of a fast additional component of the receptor potential that is absent in wild-type individuals. This may be the result of immaturity of the pigment granules in the mutants, due to the inherited absence of ommochromes. Pigment granules probably play an important role not only in the formation of the light-protective screen of the ommatidium, but also in biochemical processes considered to be responsible for the electrical passivity of the photoreceptor membrane. The possibility likewise cannot be ruled out that inherited changes in the photoreceptor membranes are connected with an imbalance between derivatives of tryptophan metabolism which participate in the generation of the cell receptor potential.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 69–75, January–February, 1982.     

Neuronal organization of the medial part of the ventral horn of the cat spinal cord

An electron-microscopic study was made of the normal structure of the medial part of the ventral horn (Rexed's laminae VII and VIII) in the cervical portion of the cat's spinal cord, the region where fibers of reticulospinal and vestibulospinal tracts terminate. Neurons of this region can be divided on the basis of the density of their cytoplasmic matrix into "light" and "dark," the dark being much more numerous in this area (26% of the total number counted) than in other parts of the gray matter of the spinal cord. The mean diameter of the soma of the dark cells is smaller than that of the light cells, and it usually is 15–20 µ. Dendrites of the neurons can also be subdivided into "light" and "dark" respectively. The surface of the former is comparatively simple in shape with a small number of appendages and spine-like structures. On the surface of the dark dendrites there are many projections and irregularly shaped lacunae. The glial cells and their processes often completely cover the surface of the soma of the small neurons, and synaptic endings are found on it only where the dendrites leave the soma. Analysis of 1000 randomly chosen synaptic endings showed that 76.1% of them form axo-dendritic synapses, 14.2% axo-somatic, and 9.7% axo-axonal synapses. Of the total number of endings 50.9% contain spherical and 40.9% flattened synaptic vesicles. Some synaptic endings contain special structures under the postsynaptic membrane and have osmiophilic synaptic vesicles. The possible functional role of the pattern of neuronal organization revealed in this region is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 176–183, March–April, 1972.     

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.     

Ionic mechanisms of nonlinearity of the retinal horizontal cell membrane

Changes in ionic conductance lying at the basis of nonlinearity of the current-voltage characteristic curve of the cell (nonsynaptic) membrane of horizontal cells were studied in experiments on the goldfish and turtle retina. All measurements were made during blocking of synaptic transmission by bright light or Co⁺⁺. An increase in the K⁺ concentration led to depolarization and to a reduction of the steepness of the hyperpolarization branch of the current-voltage curve, whereas a decrease in K⁺ had the opposite effect. Changes in the Cl^– or Na⁺ concentrations had no significant effect on membrane potential or on the shape of the current-voltage curve. The principal potential-forming ion in the horizontal cells is thus K⁺; conductance for Cl^– is absent or very low, and conductance for Na⁺ also is evidently small. In the presence of Ba⁺⁺ (2–5 mM) the steepness of the hyperpolarization branch of the current-voltage curve was increased and the whole curve became more linear. It is concluded that nonlinearity of the current-voltage curve of the horizontal cell membrane is due mainly to potential-dependent potassium channels, whose conductance increases during hyperpolarization; this increase in conductance is blocked by Ba⁺⁺. An increase in the Ca⁺⁺ concentration to 20 mM led to an increase in steepness of the depolarization branch of the current-voltage curve, suggesting that depolarization increases membrane conductance for Ca⁺⁺.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 531–539, September–October, 1981.     

Polarization and spectral sensitivity of single photoreceptors of the domestic cricket

The polarization and spectral sensitivity of single photoreceptors ofAcheta domesticus L. was measured. The morphological characteristics of the cricket rhabdome satisfy the conditions for a symmetrical model, for which the polarization sensitivity of a single photoreceptor is identically equal to the dichroism of a single microvillus. Characteristic curves of spectral sensitivity of all photoreceptors measured (24 cells) were similar and had two maxima: the principal at 500 nm and a secondary peak at 360 nm, characteristic of a pigment such as rhodopsin in the rods of the vertebrate retina. The mean value of polarization sensitivity measured was 2.28 ± 0.85 (mean ± standard deviation, 70 cells), suggesting the existence of slight preferential orientation of the dipole moments of the rhodopsin molecules along the axes of the microvilli.I. N. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 483–490, September–October, 1979.     

Changes in the electroretinogram and rhodopsin content in hunter rats during the development of hereditary degeneration of the retina

Changes in the electroretinogram were studied and the rhodopsin content determined in the retina and optic cup of Hunter rats during development of hereditary degeneration of the retina. Changes in the rhodopsin content in the retina and optic cup were found to take place differently in time. The content of visual pigment in the optic cup increased until the 45th day, and then it fell slowly; in the retina it increased until the 25th day and fell sharply after the 35th day after birth. The amplitude of the electroretinogram recorded during stimulation of all intensities from threshold to saturating fell steadily from the 17th to the 35th day; later a sharp fall in the amplitude of the response to weak stimulation with disappearance of thea wave of the electroretinogram took place. The 35th day is thus the critical period in the development of the disease. The possible role of disturbances of rhodopsin resynthesis in the phenomena observed is discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Research Institute of Human Morphology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 527–531, September–October, 1977.