Electrical feedback mechanism in the processing of signals in the outer plexiform layer of the retina.

In any chemical synapse there is an electrical feedback initiated by the electrical current generated by the postsynaptic neurone. We argue that this feedback can be rather effective in the case of invaginating synapses in the retina. A model of a dyad synapse (cone-horizontal cell-bipolar cell) is developed, in which the transfer function between the cone and bipolar cell is modulated by the synaptic current of the horizontal cell. This modulation originates by the change of the potential drop along the intercellular gap between the cone and the horizontal cell. The model takes into account the electrical coupling between the horizontal cells as well as the nonlinearity of their nonsynaptic (somatic) membrane. The model reproduces qualitatively the steady-state responses of an hyperpolarizing bipolar cell to the light spot and an annulus. It gives also the adaptational (with a light background) shift of the cone-bipolar cell transfer function. The model can be applied to depolarizing bipolar cells and to C-type horizontal cells.

Spread of potentials along the network of horizontal cells in the retina of the turtle.

The spread of potentials along electrically-coupled horizontal cell networks in the turtle retina was studied at different levels of illumination. The mean values of the stationary space constant, lambda st, measured by the steady-state responses to a bar of light moved along the retina, is about 0.13 mm for the LII horizontal cell response and 0.35 mm for the LI response. lambda st is quite stable in the physiological range of membrane potentials. The dynamic space constant, lambda (t), measured at different intervals after the onset of the light bar, transiently increased during the rising phase of the on-response. Such a transient change of lambda (t) is absent or less apparent for depolarizing responses to the offset of the light bar. Ba2+ ions strongly enhanced the transient increase of lambda (t) for hyperpolarizing responses without affecting lambda (t) for depolarizing responses. Possible mechanisms of the transient increase of the dynamic space constant are discussed.

[Letter: Velocity of passive conductance in a branching fiber]. / Skorost' passivnogo provedeniia v volokne s otrostkami

The explicit formula for the conduction velocity of the electrotonic potential in the fiber with infinitely long branches is obtained.

[Modelling the reaction of the horizontal cell layer to non-uniform light]. / Modelirovanie reaktsii sloia gorizontal'nykh kletok na neodnorodnoe osveshchenie

A mathematical model of horizontal cells in fish retina is constructed. Some conclusions and hypotheses concerning potential distribution and synaptic current are discussed.

[Rate of passive conduction in lattice structures]. / Skorost' passivnogo provedeniia v reshetchatykh strukturakh

A mathematical model of passive conduction in syncitial symmetric structures is considered. Explicit formulae of the dependence of a decrease of stationary solution and of electrotonic conduction velocity are obtained.

[Study of the electrical properties of retinal horizontal cell syncytia by the technic of uniform polarization]. / Issledovanie élektricheskikh svoistv sintsitiia gorizontal'nykh kletok setchatki metodom odnorodnoi poliarizatsii.

For uniform polarization of syncytial or cable structures at a large area with current passed via extracellular electrodes the extracellular longitudinal gradient of potential must be proportional to distance from the edge of preparation. In this paper the profile of conducting plate was found analytically which allows to obtain such a distribution of potentials. The profile is formed by hyperbola and its orthogonal asymptotes. Two polarizing electrodes are applied to places where the hyperbola is near to asymptotes. On the surfaces formed by asymptotes the gradient of potential is proportional to distance from intersection of these surfaces. Such a conducting plate was made as cavity in plexiglas filled by Ringer solution in agar. The plate was used for obtaining the voltage-current curves of horizontal cell membrane in gold fish retina. The area of uniform polarization was 4-5 mm long. Measurements inside this area allowed to determine the space constant of horizontal cell layer. The space constant measured in bright light (when resistance of subsynaptic membrane is high) depends on the membrane potential, being high (approximately 1,5 mm) during depolarization and low (0,2-0,4 mm) during hyperpolarization.

[Electric parameters of the L-type horizontal cell layer in the carp retina]. / Elektricheskie parametry sloia gorizontal'nykh kletok L-tipa v setchatke karpa.

The inner longitudinal resistance of the L-type horizontal cell syncytium in the carp retina ranges from 1.5 X 10(5) to 7,4 X 10(5) Ohm. The static resistance of the nonsynaptic membrane at the potential level corresponding to the bright light ranges from 2,5 X 10(3) to 19 X 10(3) Ohm . cm2 i.e. comparable with membrane resistances of many neurons recently investigated. Depolarization increases the resistance in 3,5 divided by 21 times up to 16 X 10(3) divided by 69.10(3) Ohm . cm2. Measured values of the capacity are 1 divided by 2 mcF . cm-2.

[Local nonuniformities in the syncytium of the horizontal cells of the retina in the turtle]. / Lokal'nye neodnorodnosti sintsitiia gorizontal'nykh kletok setchatki cherepakhi.

Electrical coupling between horizontal cells of the turtle retina was investigated by means of two microelectrodes (current and recording ones) penetrating neighbouring cells at a fixed distance from each other. The morphological coupling was revealed by means of fluorescent dye Lucifer Yellow. The electrical coupling was confirmed between elements of similar type (L1--axonal terminals, or L2--cell bodies, or R/G type cells) and no coupling was found between elements of different types, though L1 and L2 are directly connected through thin axons. In the L1 syncytium the electrical coupling at small (less than or equal to 50 microns) but fixed distances between microelectrodes could differ several times depending on the minimal displacement of microelectrodes. This local nonuniformity of coupling can be explained on the basis of structural nonuniformities in the L1 (axon terminal) network. It is unlikely however that the structural nonuniformities can influence the functional properties of horizontal cell network when the retina is stimulated adequately (by light).

[Spectral sensitivity of photoreceptors of the compound eye of the locust]. / Spektral'naia chuvstvitel'nost' fotoretseptorov slozhnogo glaza saranchi.

Intracellular recordings have shown that there are three types of receptors in the retina of the locust with lambda max = 360, 430 and 530 nm. Their spectral sensitivity curves are considerably wider than the absorption curves of the corresponding pigments. On the basis of spectral sensitivity curves obtained and assuming that each receptor contains only one pigment, possible coefficients of electrical coupling between receptors with different spectral characteristics are calculated. They correspond to coefficients of electrical coupling obtained by Shaw and Lillywhite in the locust. Thus the observed broadening of spectral sensitivity curves as compared with the absorption curves of pigments may be caused by electrical coupling between receptors.