Abstracts

Rationale: Among several pathophysiologic processes found in the development of epilepsy, the common observation of metabolic dysfunction has been suggested to contribute towards epileptogenesis. We used the multiple low dose kainate (KA) model (Hellier and Dudek 2005) of temporal lobe epilepsy (TLE) with ¹H spectroscopic imaging to evaluate the metabolic changes early after status epilepticus (SE), 3 days compared to controls. To further investigate the metabolic changes, we evaluate the effects of an oxidative phosphorylation agent methylene blue (MB) in the post-status period. Methods: Model/histology: Three groups of 180-200g male Sprague Dawley rats are studied: control, KA, KA-MB. On day 1, rats received i.p. injections of 5 mg/kg kainate hourly until 3hrs of SE was achieved; control rats received saline. SE was defined as greater than 10 class IV/V seizures (Racine scale) over a 3hr period. KA treated rats were randomly assigned to a post-SE treatment group and received either i.p. MB or saline on days 1 to 3. On day 4, animals were anesthetized, intubated, and ventilated with N₂O:O₂ (1:5 ratio) and 2% isoflurane for imaging. The rat's head was secured within a stereotaxic frame that integrated with the MR detector. Upon completion of imaging, the animal's brain was fixed with 4% paraformaldehyde. Forty µM coronal sections were stained with Nissl to assess neuronal loss and fluoro-jade B for degenerating neurons. Imaging: Scout imaging used a RARE T2 weight imaging sequence (in-plane resolution 140um). Spectroscopic imaging was performed with two sequences, moderate and short echo PRESS. A volume head coil and receiver array positioned directly over the hippocampi was used. Spatial resolution of the imaging study was 1.5mm, with nominal voxel size of 4.5ul (1.5mm x 1.5mm x 2mm slice thickness). Image guided single voxel reconstruction was used to position the voxel of interest within the hippocampus (Fig. 1). Results: As seen in Fig. 1, the KA group showed increased myo-inositol (mI), choline (Ch) and glutamine (GLN), and a small decrease in NAA in comparison to control. With methylene blue exposure, the changes in mI and GLN were less. Fig. 2 shows fluoro-jade B staining from control, KA treated and KA-MB treated rats, finding increased neuronal degeneration in the KA treated hippocampi. Conclusions: Spectroscopic imaging can detect early changes in several metabolic parameters. The increase in mI and GLN post-status are consistent with astrocytic changes, possibly reflecting edema and astrocytic injury or activation. The milder NAA decline may reflect the early process of neuronal injury consistent with fluoro-jade staining. While these data were acquired with the low dose KA model, they are consistent with Filibian 2012 in a pilocarpine model, suggesting a metabolic consistency to post-status injury.