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Background Status epilepticus‐induced hippocampal neuronal death, astrogliosis, and the activation of microglia are common pathological changes in mesial temporal lobe epilepsy (mTLE) with resistance to antiepileptic drugs. Neuronal death in mTLE gradually progresses and is involved in the aggravation of epilepsy and the impairment of hippocampus‐dependent memory. Thus, clarifying the cellular mechanisms by which neurons are protected in mTLE will significantly contribute to the treatment of epilepsy. Here, mainly using hippocampal slice cultures with or without the pharmacological depletion of microglia, we directly examined whether microglia, the resident immune cells of the brain that can act either neurotoxically or in a neuroprotective manner, accelerate or attenuate kainic acid (KA)‐induced neuronal death in vitro. Methods Hippocampal slice cultures were treated with KA to induce neuronal death in vitro. Clodronate‐containing liposomes or PLX3397 was used to deplete microglia in hippocampal slice cultures, and the effect on KA‐induced neuronal death was immunohistochemically assessed. Results The loss of microglia significantly promoted a decrease in neuronal density in KA‐treated hippocampal slice cultures. Conclusion Our results suggest that microglia are neuroprotective against KA‐induced neuronal death in slice cultures.

Aim Organotypic brain slice culture preserves the geographical position of neurons and neuronal circuits. The slice cultures also maintain both non‐neuronal cell types and the surrounding extracellular matrix. The interface method has been widely used for slice cultures, in which brain slices are placed on semiporous polytetrafluoroethylene (PTFE) membranes. However, a low optical transparency of PTFE membrane makes it difficult to perform live imaging of deep regions of slice cultures using an inverted microscope. To overcome the issue, we evaluated the suitability of using collagen membranes for slice cultures, especially focusing on live imaging of the cellular dynamics of green fluorescent protein (GFP)‐expressing microglia. Methods Entorhinohippocampal slices were cultured on either collagen or PTFE membranes. The influence of membrane type on the ability to observe deep regions of slice cultures was examined by live imaging using an inverted microscope. Results Collagen membranes were thinner and had better optical transparency compared with PTFE membranes. There were no differences in cell viability, density of neurons or microglia. The densify of visible short branches of microglia in live imaging was higher in collagen membranes than PTFE membranes. Conclusion Collagen membranes are suitable for live imaging of cellular dynamics in slice cultures using an inverted microscope.

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