[Septal Activation and Control of Limbic Structures].

Coherent activation of limbic system structures as the main function of theta-rhythm is widely discussed in the literature. However until now does not exist the common view on its generation in these brain structures. The model of septal theta-rhythmic activation and control of limbic structures is suggested basing on the literature and own experimental data.

[Restoration of long-term potentiation by food delivery to deprived rat].

The possibility of restoration of the extinguished long-term potentiation at the Shafer collaterals projections in food deprived rats to small amounts of meal was studied. Giving a small portion of meal restores a population spike's amplitude for the first CA1 response to paired-pulse stimulation. The amplitude of the population spike for the second response restored completely. Giving a small portion of meal in control groups of deprived animals without preliminary acquisition of potentiation did not produce changes of the CA1 evoked responses. Restoration of potentiation in the described experiments is likely to be related with a certain level of animal's emotional tension. It is assumed that a restoration of potentiation at natural conditions could be necessary for solution of tasks related with satisfaction of biologically important for animal needs.

[Influence of CA1 hippocampal field on theta-activity in rats under urethane anesthesia].

The influence of CA1 hippocampal field on the theta-activity production depending on the efficiency of CA1 synaptic inputs was studied in urethanized rats. The long-term posttetanic potentiation (LTP) of Shaffer collaterals resulted in an increase in the theta-power in hippocampal EEG without change in its frequency. A high correlation was shown between the increase in the theta-power and the amplitude of the local potentials induced by LTP. The mechanisms and the functional role of the observed relations between the LTP and theta activity are discussed.

[Relations between hippocampal network free oscillations and the theta activity].

The relations between the component of the hippocampal network free oscillations, i.e., sharp potential waves (SPW) and the theta component of the hippocampal EEG are considered. It is commonly accepted that, in the course of changes from the state corresponding to a weak activation of the hippocampal network in the theta rhythm by the septum through the state corresponding to a medium activation to the state of a high activation, the inverse dependence between the magnitudes of these components in the EEG spectra takes place. However, our work shows that this dependence can be deranged in the rat EEG during quiet wakefulness that corresponds to the medium activation of the hippocampal network in theta rhythm. It was also shown that the RF stimulation can evoke abnormal signals with well-pronounced theta activity against the background of a considerable SPW component. This phenomenon demonstrates a possibility of a strong derangement of the dependence, which is, as a rule, observed under the natural conditions. The hypothesis concerning the organization and regulation of the investigated components of the hippocampal EEG is proposed.

[Hippocampal activity with twofold theta-frequency].

Results obtained by the author and literature data concerning a peak of the power spectrum of hippocampal theta activity of a rat in the range of twofold theta frequency (12-20 Hz) are analyzed. The results of author's research of the signal corresponding to the second frequency group of spectrum (a twofold theta-frequency harmonic with adjoining frequency components) suggests the existence of a high-frequency component in the hippocampal theta activity regulated independently of the main theta wave. An attempt to coordinate the obtained results with the contemporary ideas about the structure of the hippocampal EEG and to explain the results of some works that does not correspond to these ideas is made. Some hypotheses about the origin and regulation of the high-frequency component of the theta activity are proposed. A particular role of the high-frequency component in different modes of activation of hippocampus is demonstrated.

[High-frequency component of hippocampal theta activity]. / Vysokochastotnaia komponenta gippokampal'noi teta-aktivnosti.

The signal corresponding to the second frequency group in spectra of the theta activity of a rat (a twofold theta-frequency harmonic with adjoning frequency components) and its regulation were studied. The level of the signal of the second frequency group was high in the theta activity diring natural orienting behavior and in desynchronized EEG during waking immobility. In some rats, the EEGs segments recorded during orienting behavior evoked by reticular stimulation contained an enhanced signal of the second frequency group (as compared to the signal of the first frequency group). The second frequency group could be also observed in the absence of the first. Estimation of signal dimension revealed two independent components in the theta activity with the high-level signal of the second frequency group. Time correlation between variations of signals of the first and second frequency groups in the theta activity accompanying natural orienting behavior was absent. These signals changed in different ways during transition from awake immobility of an animal to orienting behavior. It was concluded that in addition to the main component of the hippocampal theta activity, there exists the independently regulated twofold theta-freduency component.

[The influence of hippocampal field CA1 on the theta activity during rat orienting behavior]. / Issledovanie vliianiia polia CA1 gippokampa na teta-aktivnost' pri orientirovochnom povedeniia krysy.

The influence of CA1 hippocampal field on theta-activity production depending on the efficiency of CA1 synaptic inputs was studied in freely moving rats during their orienting behaviour. The long-term potentiation of Shaffer collaterals resulted in an increase in regularity of the theta activity due to a decrease in its amplitude-frequency modulation and variability of the waveform from cycle to cycle. Additionally, an increase in amplitude and decrease in frequency were observed. The results reveal the influence of CA1 field on the work of the septal theta activity oscillator.