Mayo Clinic researchers have found evidence that a type of resident immune cell in the brain helps protect neurons after seizures. Their results, published in Cell Reports, may provide a new target for therapies to limit the damage of seizure disorders, such as epilepsy.

Epilepsy is characterized by an electrical storm that sweeps across the brain. Medication focusing on the electrical activity within neurons is useful for many people, but not everyone. As a thunderstorm leaves debris scattered in its wake, a seizure leaves damaged neurons. Instead of being threadlike, the projections off the neuron — called dendrites — look like a beaded string, leading to their name: beaded dendrites.

From left: illustration of a microglial cell using its "arms" — called processes — to surround a beaded dendrite; a 2-photon microscopy image shows microglial process pouches (white arrows) surrounding beaded dendrites. Microglia are labeled green and neuronal dendrites are labeled in red. 

Led by Mayo neuroimmunologist Long-Jun Wu, Ph.D., this publication shows that the clean-up crew activated after a seizure, called microglial cells, also soothes dendrites, helping to protect their function. Using a type of microscope that can follow cells in a living animal, the researchers document the interaction of microglia cells with beaded dendrites after mice experienced seizure. They found that microglial cells were activated after severe seizures and used their processes to wrap around beaded dendrites. The authors named these structures microglial process pouches and showed that these structures resolve dendritic swelling after seizures.

Typically, microglial cells surround debris then engulf it with a specialized cell in preparation for digestion. But microglial process pouches wrapped around beaded dendrites stayed in place for hours, not digesting the dendrite, and then shrunk. This action was linked to the dendrite returning to its normal, threadlike state.

Dr. Wu and team write that their finding is consistent with research in experimental models of epilepsy that shows elimination of microglial cells makes seizures worse. It also supports research that suggests microglia are neuroprotective in other diseases, such as multiple sclerosis and after injury. To extend their findings, the team plans to test the molecular mechanism triggering the interaction and function of dendrites after beading is resolved. Their goal is to provide more information on the neuroprotective role of microglia after seizures to propose a new target for future therapies. For a full list of authors and funding agencies, see the paper in Cell Reports.