EN
Our previous study indicated that microinjection of procaine or electrolytic lesion of the ventral tegmental area (VTA) suppressed hippocampal theta rhythm in urethane-anaesthetized rats. The aim of this study was to verify the hypothesis that electrical stimulation of the VTA induces hippocampal theta rhythm and to fi nd brain structures particularly active during this phenomenon and probably involved in its mechanism. The study was performed on urethane anaestethized male Wistar rats with an electrode implanted unilaterally in the VTA or zona incerta (ZI – control group). Stimulation was applied as 0.1-ms rectangular impulses of 50 Hz frequency and duration of 30 s at 10-min intervals. VTA stimulation within the current intensity range of 100–240 mA evoked hippocampal theta rhythm, manifested as synchronization of the EEG signal and an increase in the power at 3–6 Hz band. ZI stimulation did not elicit such effects. After VTA stimulation we also found induction of c-fos expression in brain regions connected to the VTA: nucleus accumbens, lateral septum, or engaged in the regulation of hippocampal theta rhythm: medial septum, midline thalamic nuclei, hypothalamic nuclei, pedunculopontine, laterodorsal and cuneiform tegmental nuclei. The results indicate that the VTA may be a part of the brainstem theta synchronizing system and may infl uence the hippocampal EEG through indirect pathway via hypothalamus and the medial septum, simultaneously increasing thalamic activity.