Postictal in situ NIRS brain lactate in the rat kindling model

Objective: To determine the temporal and spatial extent of the lactate (Lac t) changes as correlated with seizure characteristics and EEG changes in th e rat kindling model. Background: Prior studies using MRS have detected cer ebral Lact postictally in animal models of seizures and in patients with in tractable focal epilepsy. Methods: We performed MRS in sham control rats (n = 4) and in rats stimulated in the right hippocampus at two different stag es of the kindling and at three time points after the seizures: <2 hours (n = 8 and 5, stage 0 and stage 5), 2 to 3 hours (n = 5 and 6), and >3 hours (n = 4 and 2). Lact/creatine (Cr) and N-acetylaspartate (NAA)/Cr ratios wer e measured in six contiguous voxels (three left, three right) covering the hippocampi, anterior and posterior regions, and compared with EEG and ictal behavior. Lact/Cr ratios were measured at a very low level in the sham con trol rats and in the >3-hour group. Results: In the <2-hour group, Lact/Cr increase was higher in stage-5 rats as compared with stage-0 rats (p = 0.00 1, unpaired t-test) and sham control rats when all the voxels were consider ed. Lact/Cr ratios were higher in the stimulated area as compared with all other brain areas in stage-0 rats (p = 0.05, paired t-test) but not in the stage-5 rats. Similar results with more inter-animal variability were measu red in the 2- to 3-hour group. NAA/Cr ratios increased significantly after stage-0 kindling in the stimulated hippocampus but not after stage-5 kindli ng. Conclusions: Postictal Lact increase as assayed by MRS correlates with EEG and behavioral seizures and suggests that it would be an additional non invasive technique for seizure localization during the presurgical evaluati on of patients with intractable focal epilepsy.