Enhanced microglial activation and proinflammatory cytokine upregulation are linked to increased susceptibility to seizures and neurologic injury in a 'two-hit' seizure model

Early-life seizures result in increased susceptibility to seizures and greater neurologic injury with a second insult in adulthood. The mechanisms which link seizures in early-life to increased susceptibility to neurologic injury following a 'second hit' are not known. We examined the contribution of microglial activation and increased proinflammatory cytokine production to the subsequent increase in susceptibility to neurologic injury using a kainic acid (KA)-induced, established 'two-hit' seizure model in rats. Postnatal day (P)15 rats were administered intraperitoneal KA (early-life seizures) or saline, followed on P45 with either a 'second hit' of KA, a first exposure to KA (adult seizures), or saline. We measured the levels of proinflammatory cytokines (IL-1β, TNF-α, and S100B), the chemokine CCL2, microglial activation, seizure susceptibility and neuronal outcomes in adult rats 12 h and 10 days after the second hit on P45. The 'two-hit' group exposed to KA on both P15 and P45 had higher levels of cytokines, greater microglial activation, and increased susceptibility to seizures and neurologic injury compared to the adult seizures group. Treatment after early-life seizures with Minozac, a small molecule experimental therapeutic that targets upregulated proinflammatory cytokine production, attenuated the enhanced microglial and cytokine responses, the increased susceptibility to seizures, and the greater neuronal injury in the 'two-hit' group. These results implicate microglial activation as one mechanism by which early-life seizures contribute to increased vulnerability to neurologic insults in adulthood, and indicate the potential longer term benefits of early-life intervention with therapies that target up-regulation of proinflammatory cytokines.