Abstracts

Rationale: The neuronal populations active during neocortical injury-induced status epilepticus (SE) are unknown. The acute injuries or insults to the cortex, such as trauma, subarachnoid hemorrhage, lobar hemorrhage, cause SE and seizure, which cause coma, worsen prognosis, delay recovery, and contribute to the development of epilepsy. These large-scale maps of brain regions during active SE will aid in understanding secondary neuronal injury caused by neocortical SE.

Methods: We followed the neocortical injury-induced SE mouse model developed by Singh et al. (2020). We implanted cobalt (Co) in the right supplementary motor cortex (M2) and 16 hours later gave a homocysteine injection (845 mg/kg, intraperitoneal) to C57Bl/6J mice to induce SE and monitored it by video and EEG. We immunolabeled whole-brain sections for cFos and NeuN, imaged them and quantified cFos immunoreactivity (IR) and its overlap with NeuN IR. We performed intra-group comparisons using t-tests with Welch’s correction for unequal variance and between-group comparisons using multiple comparisons one-way ANOVA (Bonferroni’s correction).

Results: SE started with discrete, focal intermittent seizures 15-30 minutes after homocysteine injection. CFos upregulation takes 30-45 minutes. So, we harvested brains 1 hr after homocysteine. We captured prolonged generalized convulsive seizures by harvesting brains 2 hours after homocysteine. In the early stage, cFos IR was primarily observed in the right hemisphere, ipsilateral to the Co lesion. We found differences in cFos IR between the left and the right hemispheres of several cortical and subcortical regions, including the motor cortex (p = 0.002; 4/5 animals), retrosplenial cortex (p = 0.02, 4/5 animals), somatosensory cortex (p = 0.001), anterior cingulate cortex (p = 0.0007) and amygdala ((p = 0.03). Sparse activation was observed in thalamus specifically, ventral lateral and ventral anterior nuclei (p = 0.32)), hypothalamus (p = 0.97) in both hemispheres.

We observed bilateral cFos IR in brain regions during the late stage, indicating the generalization of focal seizures. We found differences in IR between early and late stage SE in cortical regions, such as the somatosensory cortex (p < 0.0001) and the motor cortex (p = 0.0008) and subcortical regions, such as the amygdala (p = 0.007), thalamus (p = 0.001) and hypothalamus (p < 0.0001). Hippocampus was observed to have intense cFos IR, which is noticeably different from the early stage (p = 0.0013, 0.024, 0.001 for CA1, CA3, and DG, respectively).