[The effect of cadmium ions on synaptic transmission in the tectum of the frog]. / Vliianie ionov kadmiia na sinapticheskuiu peredachu v tektume liagushki.

The effect of cadmium ions on the synaptic transmission in the frog tectum was analyzed in acute experiments by the method of recording of the quantum of EEG (the extracellular monosynaptic potential of synapses of a single axon) [1]. It was shown that perfusion of the tectum with CdCl2 in the concentration of 10-200 mumol/l reversibly inhibited the quanta of EEG, decreased their duration and increased the synaptic delay. Consequently, cadmium in industrial waste may be dangerous regarding the harm to the CNS, too. The results of the presented work correspond to the supposition based on experiments in vitro that presynaptic potential-dependent calcium channels prove to be one of the areas of synaptic action of Cd++ ions.

[Properties of extracellular monosynaptic potential of a single afferent in the light of the theory of dendrites with N-shaped volt-ampere characteristics]. / Svoistva vnekletochnogo monosinapticheskogo potentsiala odinochnogo afferenta v svete teorii dendritov s N-obraznoi vol't-ampernoi kharakteristikoi.

In the frog tectum mass extracellular monosynaptic PSP of the set of synapses of one individual afferent--the quantum of EEG--was registered. Using the electrical threshold stimulation of the retina we noticed a large pair facilitation. The radial decline of the facilitated quantum of EEG was measured in order to check the conclusions of the dendritic theory which postulates the N-shaped current-voltage characteristic of the membrane. Therefore, we synchronously derived conditional and test quanta of EEG in the centre and 40-60 microns peripherally of terminal axonal arborization. In a half of the experiments the test quantum of EEG twice as large as the conditional one radially declined 25% less. The half-width and rise-time of the test quantum of EEG were longer as compared with the conditional one, especially in the peripheric derivation, the difference being about 1 ms. The totality of our results agrees with the concept of electrically excitable inward current in non-synaptic membrane of the apical dendrites in the tectum. The current is predicted by the theory of the N-shaped current-voltage characteristic of dendrites.

[Paired facilitation of the summated extracellular synaptic potentials of individual retino-tectal fibers in the frog]. / Parnoe oblegchenie summarnykh vnekletochnykh potentsialov sinapsov odinochnykh retino-tektal'nykh volokon liagushki.

The paired-pulse facilitation of the EEG quanta (the extracellular monosynaptic PSPS of all synapses of one axon) was examined in layer F of the frog tectum at normal and at increased concentrations of external Ca or Mg ions. The maximum values of facilitation were observed with intervals between stimuli of about 5 ms. Under normal conditions the amount of maximal facilitation was different for separate EEG quanta and varied from 1.4 to 2.4. Distribution of the EEG quanta by the amount of maximal facilitation had two modes at the values fmax = 1.65 and 1.95. The time course of facilitation could be approximated by two exponential components with the time constants of decays tau 1 = 5-6 ms and tau 2 = 140-150 ms for more facilitated EEG quanta, and tau 1 = 6-8 ms and tau 2 = 60-70 ms for the others. Nonequal degree of facilitation of separate EEG quanta and experiments with increased external Ca2+ and Mg2+ concentrations have suggested the dependence of paired-pulse facilitation on the quantum content of the transmitter released in retinotectal synapses. Two types of terminal arbors of axons whose synapses differ in quantum content are supposed to exist in the tectum layer F.

[Discharges of neurons of the frog tectum during electric stimulation of individual retinal ganglion cells]. / Razriady neironov tektuma liagushki pri élektricheskoi stimuliatsii otdel'nykh ganglioznykh kletok setchatki.

In the frog optic tectum, at the depth of 200-270 micron extracellular monosynaptic PSPS of one axon were recorded under threshold electrical stimulation of the retina by a short train of stimuli. The latency of presynaptic spike was 8-12 ms. At a 5-25 ms interval between successive stimuli a negative spike was observed on the top of the testing EEG quanta enlarged 1.5-2.5 times. This spike is considered to be a population discharge evoked by the firing of a single fibre of the optic tract. This fibre terminates in layer F or G, while the population spike is generated by the tectum units of layers 6-8. A possibility that the firing of the 3d-5th class detectors excites tectal ganglionic cells whose axons form the main part of the tectobulbospinal tract is discussed.

[Mass extracellular monosynaptic potential of synapses of a single axon in the optic thalamus of frogs upon electric stimulation of the retina]. / Summarnyi vnekletochnyi monosinapticheskii potentsial sinapsov odnogo aksona v zritel'nom bugre liagushki pri élektricheskoi stimuliatsii setchatki.

Mass extracellular monosynaptic PSP of one axon synapses ("EEG quantum") were reliable recorded in the frog thalamus as "all-or-none" potentials up to 250 muV at threshold electrical stimulation of the retina. The degree of facilitation of the second response was measured during paired-pulse stimulation. The ratio of the testing PSP amplitude to the conditioning one dependent on the signal amplitude. The ratio reached 250% at interstimulus interval of 5 ms with amplitude of conditioning PSP being about 50 muV.

[Summarized extracellular postsynaptic potential of a single axon, an EEG quantum in the rabbit neocortex]. / Summarnyi vnekletochnyi postsinapticheskii potentsial odnogo aksona--kuvanta EEG v néokortekse krolika.

The possibility to record an EEG quantum following negative spikes with small amplitude was studied in the rabbit's neocortex. In about half of the averagings of the focal post-spike ECoGs recorded with a low-resistance microelectrode the spike was followed by a microsignal of synaptic form. The small amplitude and the negative sign of the spike's main phase pointed to a true extracellular leading off of biopotentials. A relatively small ratio between the amplitudes of the spikes and the post-spike signals shows that the latter are not afterpotentials of the spikes. They do not reflect discrete PSPs of single synapses, because they were recorded with relatively thick microelectrodes. The latency of the post-spike signals corresponded to their monosynaptic nature. Hence, the recorded signals are the EEG quanta. Their recording is a relatively simple procedure.