[Intracellular tetanization by the hyperpolarizing current potentiates synapses formed by mossy fibers on the pyramidal cells of the CA3 hyppocampal area of the rat].

Whole-cell recordings of excitatory postsynaptic potentials evoked by the minimum stimulation of mossy fiber inputs were performed in CA3pyramidal neurons in rat hippocampal slices. Paired responses were recorded before and after intracellular hyperpolarization tetanization. This procedure produced an increase in excitatory postsynaptic potentials at least for 20-min recording period. The effect, referred to as hyperpolarization-tetanization-induced long-term potentiation, could arise without simultaneous mossy fiber stimulation and revealed signs ofpresynaptic origin. Loading Ca2+ chelator BAPTA into the postsynaptic neuron completely prevented this form oflong-term potentiation. The findings suggest that whereas the induction of hyperpolarization-tetanization-induced long-term potentiation was postsynaptic, its expression was presumably presynaptic. The results show the significance ofgamma-rhythmical hyperpolarizing oscillations for changes in synaptic input efficacy and the role ofa network in cellular mechanisms of plasticity.

[Study of giant depolarizing activity in the neonatal hippocampal neurones]. / Issledovanie mekhanizma vozniknoveniya gigantskikh depoliariziruiushchikh potentsialov v neironakh gippokampa novorozhdennykh krys.

Spontaneous oscillatory activity is a general feature of developing neural networks. Early in postnatal development, spontaneous network-driven events, termed giant depolarizing potentials (GDPs), occur synchronously over the entire hippocampus. By performing simulation of hippocampal network with using physiology parameters of the neurons and its network from the present experiments and literature dates, we investigated the participation of the different components of network in the generation of GDPs. Comparing the results of the model and in vitro experiments we conclude that are necessary for the GDP generation involvement the activation of GABAergic, glutamatergic inputs and perhaps gap junction.

[Study of synaptic plasticity of hippocampal CA3 area as a result of tetanization of perforant path]. / Issledovanie sinapticheskoi plastichnosti oblasti CA3 gippokampa pri tetanizatsii perforantnogo puti.

Evoked responses in CA3 area to the mossy fibers stimulation were studied after low and high frequency tetanizations of the perforant path. Stimulations of perforant path with 10 and 100 Hz frequencies inducted depression testing through the same path. Subthreshold for potentiation of the mossy fibers inputs to the CA3 tetanization of the perforant path with 10 Hz frequency transformed to threshold one after previous tetanization of the perforant path with 100 Hz frequency. Tetanization of the mossy inputs to the CA3 with 10 Hz frequency leaded to potentiation whereas tetanization with frequency 100 Hz depressed the same inputs. High frequency tetanizations (100 Hz) of the perforant path with theta-rithm frequency stimulation basically depressed of the CA3 evoked responces to the mossy fiber stimulation.

[Modulating influence of adenosine triphosphate on the oscillating properties of hippocampal neurons during early ontogenesis]. / Moduliruiushchee vliianie adenozintrifosfata na ostsiliatornye svoistva gippokampal'nykh neironov v rannem ontogeneze.

Extracellular ATP was used to test the involvement of purinergic P2 receptors in the modulation of GAB Aergic giant depolarizing potentials (GDPs) in rat neonatal hippocampus. Bath application of ATP reduced the GDP frequency in a concentration-dependent manner. The inhibitory effect of ATP persisted in the presence of adenosine P1 receptor antagonist DPCPX indicating the action of ATP on GDPs. It was suggested that, during development, ATP can modulate network-driven activity in the neonatal hippocampus through the activation of purinergic P2 receptors.

[Long-term potentiation of AMPA- and NMDA-components of minimal postsynaptic currents in CA1 area of the rat hippocampus]. / Dolgovremennaia potentsiatsiia AMPA- i NMDA-komponent minimal'nykh postsinapticheskikh tokov v oblasti CA1 gippokampa krys.

Excitatory postsynaptic currents (EPSC) were recorded from pyramidal neurons of the rat hippocampal slices as well as the AMPA and NMDA components. A strong enough correlation between the amplitudes of the components provided a reliable evidence of their generation by the same synapse. Both components revealed similar LTP following afferent tetanisation. The data obtained do not support postsynaptic mechanisms of the LTP maintenance but suggest that increased presynaptic release represents a basic mechanism of the early LTP maintenance.

[Reverberation of excitation in "hippocampus-entorhinal cortex" slices in rats. Optical recording]. / Reverberatsiia vozbuzhdeniia v perezhivaiushchikh srezakh "gippokampal'naia formatsiia-éntorinal'naia kora" krys. Opticheskaia registratsiia.

Using RH155 voltage-sensitive dye and photodiode array for optical recording, responses to electrical stimuli were investigated in rat brain slices, which included hippocampus and entorhinal cortex. It was shown that single electrical stimulation of the entorhinal cortex, subiculum, or dentate gyrus evoked a potential consecutively spreading from the dentate gyrus to the CA3 and then CA1 hippocampal areas. When the GABAergic inhibition was partially blocked by picrotoxin, the first excitation wave was followed by additional several waves. Such secondary waves were observed in all the hippocampal areas with a constant trial-to-trial latency shift increasing in the direction from the dentate gyrus to CA3 and CA1 areas. Reverberation of activity between the hippocampus and entorhinal cortex is regarded as the most probable cause of appearance of the secondary excitation waves.

[The generation of action potentials in the terminals of the Schaffer collaterals during long-term potentiation in the CA1 region of the hippocampus]. / Generatsiia potentsialov deistviia v okonchaniiakh kollateralei Shaffera vo vremia dlitel'noi potentsiatsii v oblasti CA1 gippokampa.

Experiments were performed in rat hippocampal slices. Activity of individual CA3 pyramidal neurons and field potentials in the CA1 areas were recorded extracellularly. The collision technique was applied to detect the antidromic origin of the background action potentials in the somata of CA3 neurons. Threshold stimulation of terminals of the Schaffer collaterals in the stratum radiatum of the CA1 area was applied to study their excitability during the CA1 long-term potentiation. During the long-term potentiation, antidromic action potentials appeared in the somata of the CA3 neurons. The obtained evidence suggests that the synaptic potentiation is accompanied by an enhancement of axon terminal excitability resulting in generation of the action potentials.