ИСТИНА

Purpose: The aim of this study was to investigate cortical pattern and incidence of thalamo-cortical oscillations after transient unilateral physiological cortical inactivation in WAG/Rij rats. Method: A single unilateral cortical spreading depression (SD) was used as a temporal functional inactivation of the cortex. It was induced by injection of 5% KCl in the occipital cortex of awake WAG/Rij rats (n=12), control rats received sham microinjections. Rats were equipped with six recording stainless-steel electrodes placed bilaterally over the frontal, somatosensory and parietal cortex. EEG was recorded for one hour before (baseline), immediately after (experiment), and 24 hours after (recovery) SD initiation. The successful induction of SD in cortex was verified by spectral analysis of EEG by fast Fourier transformation method in MatLab program on 20-second segments of EEG; SDs were detected based on a brief (1-2 minute) slump of gamma-activity. Results: A significant (p<0.01) increase in number and mean duration of sleep spindles (SS), spike-wave spindles (SW spindles) and decrease in SWDs in both hemispheres was found in the hour after unilateral single cortical SD. Unilateral SS, SW spindles and SWDs reappeared first in the contralateral somatosensory cortex. SS and SW spindles were also quicker to return than SWDs in the contralateral hemisphere. Bilateral SWDs, SS and SW spindles reappeared later than unilateral SWDs, SS and SW spindles, and in the same chronological order as in the contralateral hemisphere. Next day all oscillations returned to baseline except SW spindles. Conclusion: Transient changes of functional state even in one hemisphere lead to a suppression of non-convulsive epileptic activity in both hemispheres and this suggests that a functional integrity of interhemispheric cortico-cortical and cortico–thalamo-cortical network for generation of bilateral occurring SWDs is necessary. The appearance of first SWDs in the somatosensory cortex confirms the crucial role of the somatosensory cortex in generation of SWDs. The fast return of sleep spindles might be due to their thalamic origin and that in contrast to SWDs, a complete intact cortex is not a requirement for their presence.