Abstracts

We used an 11.1 Tesla (T) magnet to determine in vivo temporal hippocampal and parahippocampal structural changes in the latent period of epileptogenesis in a rat model of mesial temporal lobe epilepsy. We also determined if chronic microelectrodes distort MR images to assess the feasibility of MRI with electrophysiological arrays., Fifty micron gold plated tungsten wires (2) were implanted in the ventral hippocampus in Sprague Dawley rats (n=4). Spontaneously seizing rats were obtained following experimentally inducted status epilepticus (SE). Rats were video recorded to capture spontaneous seizures. An MRI compatible stereotaxic frame was developed, to allow repeatable positioning under isoflurane in the 11.1T/40 cm bore magnet, along with a 3 cm, 150 degree arc, linear surface MR coil. Rats were imaged pre/post wire implantation and after SE at 3, 5, 7, 10, 20, 40, 60 days. T2-weighted images were collected and quantified., Brain images and wire locations were obtained with the stereotaxic frame, which provided a repeatable platform. Significantly increased T2 values were observed in the amygdala, entorhinal and piriform cortices, particularly on the contralateral side to stimulation, in three out of four rats. T2-weighted images of the first rat showed a contralaterally growing volume of hyper-intense tissue in the hippocampus and amygdala (Fig. 1). The brain of the second rat did not change; the wires were medial to the hippocampus near the alveus. The third rat showed hyper-intensity in the contralateral amygdala, with wires in the ventral hippocampus. The fourth rat was hyper-intense in both sides of the hippocampus and amygdala by day 3, but slightly decreased in time, with wires in the hippocampus near the alveus., Unilateral electrically induced SE produces bilateral structural changes in the hippocampal and parahippocampal structures. Stereotaxic images allowed repeated measures of the structural changes during epileptogenesis. The implanted wires produced minimal distortions. Their positioning in the ventral hippocampus may play a role in which structures show changes. Future work will relate the physiological and structural changes during epileptogenesis using electrophysiology and high resolution MRI.[figure1], (Supported by NIH grant R01 EB004752, Wilder ERC, UF Alumni Foundation.)