Rate of interictal events and spontaneous seizures in epileptic rats after electrical stimulation of hippocampus and its afferents

Purpose: Deep brain stimulation has been used by several investigators to prevent the occurrence of spontaneous seizures in patients with intractable epilepsy. With the kainic acid rat model of spontaneous recurrent seizures, we examined the consequences of subthreshold electrical stimulation of commissural pathways and perforant path on the synaptic plasticity, rate of interictal epileptiform events (IIEs), and spontaneous seizures in kainic acid (KA)-treated rats epileptic rats. Methods: Recording microelectrodes were implanted bilaterally in the dentate gyrus and entorhinal cortex. Stimulating electrodes were implanted into the rostral part of the right hippocampus and right perforant path. Stimulation was performed daily with 200 Hz/0.5-s duration trains, 10-min duration 1-Hz train, or 2-h, 1-Hz train and 2-h duration, 50-Hz trains. Integrated amplitude of evoked potentials, rate of IIE, and spontaneous seizures was analyzed before and after stimulation. Results: High-frequency tetani evoked long-term potentiation in 50% of epileptic rats compared with 100% of control rats. No long-term depression was observed after 1-Hz train. Decrease rate of HE was found during 1-Hz and 50-Hz stimulation and returned to the basal level within 30-60 min. No significant change of the spontaneous seizure rate was found. Conclusions: Epileptic brain is less prone to plastic changes compared with the normal brain. Daily 2-h electrical stimulation with either low or high frequency does not have a long-term effect on the rate of interictal events and spontaneous seizures.