EN
INTRODUCTION: Hippocampal (HPC) theta rhythm may be important for various phenomena, including attention and acquisition of sensory information. Two types of HPC theta (types I and II) exist based on pharmacological, behavioral, and electrophysiological properties. Both types occur in conscious animals, whereas only type II (atropine-sensitive) theta is present under anaesthesia. The circuit of HPC theta synchronization includes the medial septum-diagonal band of Broca (MSDB), with cholinergic and GABA-ergic neurons comprising the two main projections from MSDB to HPC. Just recently we have demonstrated that vagal nerve stimulation (VNS) induces HPC type II theta in urethanized rats. AIM(S): The primary aim of the present study was to assess the effects of cholinergic MSDB inhibition on VNS induced HPC theta rhythm. METHOD(S): Anesthetized rats were implanted with vagal bipolar cuff electrode. VNS parameters were constant: pulse duration (1.0 ms), train duration (10 s), frequency (10 Hz) and pulse intensity 8 mA. Monopolar tungsten electrodes were implanted into HPC in accordance to standard stereotactic technique. HPC field potential was analyzed of off‑line using the Spike‑2 software computing system (CED, Cambridge, UK). In a separate experiments cholinergic, surface only during stimulation. VNS intensity was tested in a range: 0.2–10.0 mA. Remaining parameters were constant: pulse duration (1.0 ms), train duration (10 s), frequency (10 Hz). RESULTS: We demonstrated that the chronically implanted vagal cuff electrode decreased (vs tungsten electrode) the amplitude of HPC type II theta in 30%. The effect of different types of electrodes used for VNS was also noticed in the evaluation of HPC theta threshold. CONCLUSIONS: The type of the stimulation electrode (cuff vs. tungsten) used determines the final effect of VNS on hippocampal field potential.