Abstracts

In this study, we used MR diffusion tensor imaging (DTI) to determine the temporal hippocampal and parahippocampal structural changes in vivo at 11.1 Tesla (T) during the latent period of epileptogenesis and to examine these same regions in the excised intact brain at 17.6 T. The mesial temporal lobe model was also used to determine if chronic stimulating/recording microelectrodes distort MR images collected at 11.1 T., Fifty micron gold plated tungsten wires (2) were implanted in the ventral hippocampus in Sprague Dawley rats (n = 6). Spontaneously seizing rats were obtained following experimentally inducted status epilepticus (SE). Rats were video recorded to capture spontaneous seizures. Injured rat brains were examined in vivo at 11.1 T pre/post wire implantation and after SE at 3, 5, 7, 10, 20, 40, 60 days. The intact excised brain of 2 rats were imaged at 17.6 T. Diffusion weighted images were acquired using gradient directions specified by the tessellations of an icosahedron on the hemisphere. The diffusion weighted images were fit to a rank-2 tensor model of diffusion., Five of the 6 rats developed seizures. The DT images of the rat, without seizures, looked identical to controls. In the other 5 rats, diffusivity increased in the hippocampus and fimbria in vivo. In 2 of these rats, diffusivity also increased in the entorhinal cortex. Increased diffusivity was seen as early as day 7 post-stimulation. We examined the excised brains of a seizing rat and one that did not. In the seizing rat, the diffusivity increased bilaterally in the hippocampal region, identified with mossy fiber sprouting. The hippocampus showed atrophy ipsilateral to the simulation. Decreased fractional anisotropy indicated a loss of structure in the dentate gyrus and CA2/3 region of the pyramidal cells (Fig.1)., The induced SE produces bilateral structural changes, visible in detail with DTI, in the hippocampal and parahippocampal structures. Stereotaxic images allowed repeated measures of the structural changes during epileptogenesis and the implanted wires produced minimal distortions. Future work will relate the physiological and structural changes, during epileptogenesis, using electrophysiology and DTI.[figure1], (Supported by NIH grants, R01 EB004752 and R01 NS42075, Wilder Epilepsy RC, and the UF Alumni Foundation.)