Electrode implantation and EEG recording

For the recording of the electrical activity of the brain, electrodes were implanted in rats (n = 15 per group) on P28. The rats were anesthetized with 10% chloral hydrate (3 ml/kg) and then fixed into the stereotaxic apparatus. The electrodes were bipolar twisted silver steel and embedded in the skull with dental cement. These electrodes were implanted into the bilateral hippocampal CA3 (3.5 mm posterior to bregma, 3.5 mm lateral, 3.5 mm ventral to the dura mater), according to the coordinates derived from the atlas of Paxinos and Watson. Spontaneous EEG seizures in the dentate gyrus were recorded in freely moving animals after 3 days of recovery, which were then individually placed in a cage and connected to a neurophysiology workstation (AD Instruments Lab Chart 8) through a flexible cable that prevents twisting [51]. The frequency and mean duration of these spontaneous EEG seizures during an EEG recording session were examined for 2 h. The EEG signals were digitized with Lab Chart software (AD Instruments). Seizure severity was classified into five levels by Racine’s scale [52]: I, facial movement; II, head nodding; III, unilateral forelimb clonus; IV, bilateral forelimb clonus; V, tonic clonic seizure, rearing, and failing. The rats in which seizure severity reached a level III were identified as grand mal seizure disorder. Seizures were also identified by consistent changes in the power of the fast Fourier transform of EEG, including changes in the frequency of activity during the course of the event. These criteria have been used successfully by experts in the field [53].