Microglia on Leave: PLX5622 Reveals Immune Neuronal Crosstalk in Epilepsy and Behavioral Comorbidities

Background: Neuroinflammation is implicated in epilepsy pathogenesis, and microglia are key immune cells of the brain that participate in neuroinflammatory responses associated with epilepsy.This study investigated the role of early microglial activation following an epileptogenic brain injury on the incidence and severity of epilepsy and associated neurobehavioral impairments in a model of acquired epilepsy.Methods: Status epilepticus (SE) was induced in male C57BL/6 mice via electrical stimulation of the ventral hippocampus, while additional mice were enrolled as sham controls (n = 125 total).Following termination of SE, mice received injections of the colony-stimulating factor 1 (CSF1) receptor inhibitor PLX5622 (PLX; 50 mg/kg IP twice daily) to suppress microglial activation caused by SE, or vehicle, for seven days.At the end of treatment, the effect of microglial suppression on the neuroinflammatory response to SE was characterised using gene expression, immunohistochemistry, and flow cytometry.Additional mice were followed for four months and underwent a series of neurobehavioral tests and epilepsy assessment.Results: PLX treatment significantly reduced Iba1 + cell counts, reduced GFAP + immunoreactivity, and downregulated the expression of proinflammatory cytokines in the hippocampus compared to vehicle following SE, intimating that the neuroinflammatory response of SE was suppressed by PLX.Flow cytometry revealed that SE significantly reduced microglial expression of CX3CR1 and CD206, but increased expression of CD16/32, shifting microglia towards a pro-inflammatory state.However, PLX treatment did not influence the relative expression of these genes.In the chronic stage, SE mice treated with PLX exhibited improved spatial memory (Y-maze test: p = 0.0016) and reduced depressive-like behavior (tail suspension test: p = 0.04; sucrose preference: p = 0.14) compared to vehicle-treated SE mice.However, PLX treatment did not alter the incidence of epilepsy after SE (58% in vehicle-treated mice vs 50% PLX treated mice; p = 0.65) or seizure frequency in epileptic animals.Conclusion: Suppression of microgliosis with PLX eliminates the neuroinflammatory response after SE, and this is associated with prevention of long-term behavioral impairment.However, this intervention does not influence the development of epilepsy.These results demonstrate that acquired epilepsy and its behavioral comorbidities have different pathogenic mechanisms after SE, with early microglial driven neuroinflammation most relevant to the latter.