Spike-induced cytoarchitectonic changes in epileptic human cortex are reduced via MAP2K inhibition

Interictal spikes are electroencephalographic discharges that occur at or
near brain regions that produce epileptic seizures. While their role in
generating seizures is not well understood, spikes have profound effects
on cognition and behavior, depending on where and when they occur. We
previously demonstrated that spiking areas of the human neocortex show
sustained MAPK activation in superficial cortical layers I-III and are
associated with microlesions in deeper cortical areas characterized by
reduced neuronal nuclear protein (NeuN) staining and increased microglial
infiltration. Based on these findings, we chose to investigate additional
neuronal populations within microlesions, specifically inhibitory
interneurons. Additionally, we hypothesized that spiking would be
sufficient to induce similar cytoarchitectonic changes within the rat
cortex and that inhibition of MAPK signaling, using a MAP2K inhibitor,
would not only inhibit spike formation but also reduce these
cytoarchitectonic changes and improve behavioral outcomes. To
test these hypotheses, we analyzed tissue samples from 16 patients with
intractable epilepsy who required cortical resections. We also utilized a
tetanus toxin-induced animal model of interictal spiking, designed to
produce spikes without seizures in male Sprague-Dawley rats. Rats were
fitted with epidural electrodes, to permit EEG recording for the duration
of the study, and automated algorithms were implemented to quantify
spikes. After 6 months, animals were sacrificed to assess the effects of
chronic spiking on cortical cytoarchitecture. Here, we show that
microlesions may promote excitability due to a significant reduction of
inhibitory neurons that could be responsible for promoting interictal
spikes in superficial layers. Similarly, we found that the induction of
epileptic spikes in the rat model produced analogous changes, including
reduced NeuN, calbindin, and parvalbumin-positive neurons and increased
microglia, suggesting that spikes are sufficient for inducing these
cytoarchitectonic changes in humans. Finally, we implicated MAPK signaling
as a driving force producing these pathological changes. Using CI-1040 to
inhibit MAP2K, both acutely and after spikes developed, resulted in fewer
interictal spikes, reduced microglial activation, and less inhibitory
neuron loss. Treated animals had significantly fewer high-amplitude,
short-duration spikes, which correlated with improved spatial memory
performance on the Barnes maze. Together, our results provide
evidence for a cytoarchitectonic pathogenesis underlying the epileptic
cortex, which can be ameliorated through both early and delayed MAP2K
inhibition. These findings highlight the potential role of CI-1040 as a
pharmacological treatment that could prevent the development of epileptic
activity and reduce cognitive impairment in both patients with epilepsy
and those with non-epileptic spike-associated neurobehavioral disorders.