MR spectroscopy predicts injury in a variable rat model of epilepsy
Yijen Wu1, Patrice S Pearce2, Amedeo Rapuano3, Kevin Kelly2, Nihal de Lanerolle3, and Jullie W Pan4

1Developmental Biology, University of Pittsburgh, Pittsburgh, PA, United States, 2Pittsburgh, PA, United States, 3New Haven, CT, United States, 4University of Pittsburgh, Pittsburgh, PA, United States


MR spectroscopy in a variable rat status epilepticus (kainate induced) model of epilepsy is shown to segregate between mildly and severely injured animals. As measured 3days after status epilepticus, animals with NAA/tCr values of less than 1.0 (kainate more injured, KMI) segregated with greater increases in Inositol/tCr, Glutamine/tCr and Lac/tCr, with these changes predicting the metabolic measured 3weeks after status. Although Inositol/tCr was elevated in the kainate less injured KLI group, the KLI group showed milder changes at 3days and at 3weeks. This metabolic classification was also sustained into histologic studies.


Several models of epilepsy based on chemoconvulsant exposure or electrical stimulation use a lengthy seizure period, which after a variable latent period of 1 to 3weeks, results in spontaneous recurrent seizures. However it is known that the specific duration of the status epilepticus is an important factor, with seizures lasting longer than 40-50min causing discrete differences in pathology and gene expression (1). In this report we implement a short seizure model of rat epilepsy (2) and find spectroscopic changes that predict subsequent histology and metabolism.


A short variant of the rat Hellier-Dudek (3) intraperitoneally injected kainate (KA) model of temporal lobe epilepsy was used. After initiation of a stage 3/4/5 seizure, continuing status epilepticus was maintained for 45min after which 20mg/kg diazepam was administered for recovery. Animals were then evaluated twice by MR, 3days and 3weeks after status during the epileptogenesis period. Controls were similarly treated with sterile saline. A Bruker Biospec 7T 40cm horizontal MR system was used with a 72mm volume transmit coil and 2 element receive array. T2 RARE was acquired for positioning of the hippocampus (Fig.1). Over the hippocampal slice, Bolero was used for B0 shimming (3), achieving homogeneity of 5.8±1.0Hz. Single voxel MR spectroscopy was acquired from 8μl voxels with TR/TE 1.7s/10ms (17min per acquisition) from the left, right dentate gyrus (DG) and CA3 regions. LCM analysis was performed for determination of the metabolite profiles, accepting Cramer Rao limits of <15%. A subset of animals (n=8) was sacrificed after 3weeks for histological analysis.


Fig. 1 shows the positions of the dentate gyrus (DG), CA3 voxels and corresponding DG spectra from a single rat studied at 3days and 3weeks. At 3days, all treated rats (n=21) showed a significant decline in NAA/tCr, increased Ins/tCr, Gln/tCr and Lac/tCr in comparison to control (n=10). Given the possibility that these animals might show substantially variable injury, we evaluated the animals using a histogram analysis with the 3day DG data. As shown in Fig2A (for each animal there is a left and right measurement), a large number of the kainate treated animals exhibited a comparatively normal NAA/tCr, while a minority exhibited low values (<=1.0), this seen in spite of the group increase in Ins/tCr (consistent with occurrence of status). The distribution appears distinct from the control animals (n=10). As the lowest value from the control animals was above 1.0, this was used as the threshold value to segregate the kainate treated animals. To demonstrate this specific behavior from NAA/tCr, Fig2B shows the equivalent histogram for Ins/tCr, which appears to be more consistent with a single group with a large variance. Of the n=21 KA treated rats, a 3day NAA/tCr threshold of 1.0 in the DG separated the animals into n=6 (“KA more injured” KMI with NAA/tCr<1.0) and n=15 (“KA less injured” KLI, NAA/tCr>1.0). This segregation is reflected in the other metabolite changes and the 3week data (Fig. 3). At 3days, the KLI and KMI groups differed significantly from control in Glu/tCr, Ins/tCr, Gln/tCr and Lac/tCr. The majority of these changes are consistent with the KMI group experiencing more intense status and/or slower recovery from the status, with increased inositol, glutamine and lactate. The separation of the KLI and KMI groups persisted into 3weeks. Both groups exhibited some recovery of NAA/tCr, but KLI returned to control values at 1.28±0.12, while the KMI group NAA/tCr value stayed depressed at 1.00±0.12 (control, 1.30±0.15). The 3week KMI group also continued to show a increased Ins/tCr and a decreased Glu/tCr. In contrast, the 3week KLI group had largely normalized all of its metabolic parameters. Histologically, a blinded semi-quantitative Nissl analysis of the dorsal hippocampus was performed in n=8 treated rats, finding that the KLI group (n=4) to be largely intact while the KMI (n=4) group typically showed neuronal loss and gliosis. Overall, the histological data suggest that the 3day segregation by NAA/tCr is predictive towards the 3week histological features of gliosis and Nissl loss.


Using a short version Hellier Dudek model, the 3day MR spectroscopic measurement of NAA/tCr can separate the less and more severely injured animals. This is based on the numerous 3day, 3week parameters and histology that are consistent with the KLI or KMI categorization and argues for a key role of neuronal mitochondria and metabolic dysfunction in describing or predicting tissue response in the post-status period. Whether or not NAA/tCr can predict development of epilepsy or cognitive injury after seizures will require additional work.


Financial support is acknowledged from NIH NS083035, EB011639, NS090417.


1. Norwood BA, Bauer S, Wegner S, Hamer HM, Oertel WH, Sloviter RS et al. Epilepsia. 2011 Sep;52(9):e109-12.

2. Hellier JL, Dudek FE. Curr Protoc Neurosci 2005 9:9-19.

3. Miyasaka N, Takahashi K, Hetherington HP. J Magn Reson Imaging. 2006 Oct;24(4):908-913.


Fig 1. Scout (A) showing loci for the dentate gyrus (DG) and CA3-CA1 (CA) voxels. Corresponding spectra acquired at 3days (B) and 3weeks (C) are shown from single survival rats, showing matched control and two KA rats. Identified metabolites are shown in the control 3day spectrum. The arrows on the “more injured” 3day spectra show a decreased NAA, increased Ins. The “less injured” 3day spectra show primarily the increase Ins.

Fig 2. Histograms of NAA/tCr (top) and Ins/tCr (bottom) values from all animals. The KA animals show a bimodal distribution for NAA/tCr. Note that for each animal there is a left and right measurement. With a <= 1.0 threshold for NAA/tCr, there is a total of 12 measurements defining the KMI group.

Fig 3. Group means and standard deviations showing the control (blue), KLI (green) and KMI (red) data at 3days and 3weeks after status epilepticus. Because NAA/tCr is used to directly define the KLI and KMI groups, no significance testing is performed between these groups for NAA/tCr. *p < 0.05 with control; ^p < 0.05 between KLI and KMI. The solid bars are 3day data; the cross hatched bars are week data.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)