Abstracts

Rationale: In the presurgical evaluation for patients with refractory epilepsy, invasive EEG using depth electrodes or subdural grid electrodes may be required to accurately localize the epileptogenic focus. Although the signal quality and spatial resolution of invasive EEG is high, there are risks associated with the neurosurgical procedure required for implantation of the electrodes. Therefore, a less invasive method for recording high-quality EEG would be of interest. Intravascular EEG, measured by recording from electrodes introduced through venous or arterial catheterization of the brain, has been proposed as an alternative to invasive EEG. Recently it has been shown that the signal quality of intravenous EEG is comparable to subdural EEG in pigs. The feasibility of intravascular EEG recording in rats has never been demonstrated. Nevertheless, the possibility of recording intravascular EEG in rats would be of interest as it would enable long-term intravascular EEG recording in models of spontaneous recurrent seizures. In this proof of concept study, we aimed to show the feasibility of both intravenous and intra-arterial EEG recording in rats.Methods: Two Wistar rats (male, ca. 350g) were used. The rats were anesthetized with isoflurane during the complete experiment. In the first rat the superior sagittal sinus was exposed through a small craniotomy. Next, two teflon-coated stainless steel electrodes (60 µm diameter) were inserted. A bipolar stainless steel electrode was also implanted just below the cortical surface approximately 5 mm lateral to the intravenous electrode. EEG was then recorded on both electrodes. In the second rat, a single teflon-coated stainless steel electrode (110 µm diameter) was inserted in the right common carotid artery and advanced up the internal carotid artery as far as possible. A subcutaneous electrode was used as reference electrode for EEG recording. In both rats, the depth of anesthesia was varied by modulating the isoflurane concentration. In the first rat, a local intracortical injection of kainic acid (3 µg) was given in the cortex to provoke epileptiform discharges. After 30 min, an intraperitoneal injection with ketamine 50 mg/kg was given to reduce the epileptiform activity. In the second rat a CT scan was acquired after the experiment to determine the location of the intra-arterial electrode.Results: Brain CT confirmed intracranial localization of the intra-arterial electrode in the second rat. In both rats, modulation of the depth of anesthesia correlated to changes in the intravenous and intra-arterial EEG. There were no significant pulsation artefacts related to blood flow. The intravenous EEG acquired in the first rat showed close resemblance to the cortical EEG recorded from the nearby cortical electrode. After injection of kainic acid, spikes were observed on the intracortical as well as the intravenous EEG recording. Injection of ketamine led to suppression of the epileptiform activity.Conclusions: The feasibility of recording intravenous and intra-arterial EEG in rats was demonstrated. On intravenous EEG, the registration of epileptiform discharges was also demonstrated.