The extent of damage following repeated injury to cultured hippocampal cells is dependent on the severity of insult and inter-injury interval

Recent evidence suggests repeated mild brain trauma may result in cumulative damage. We investigated cell damage and death in hippocampal cultures following repeated mechanical trauma in vitro by measuring propidium iodide (PrI) uptake, release of neuron-specific enolase (NSE) and glial S-100beta protein, and performing neuronal counts. Cultures receiving two mild injuries (31% stretch) 1 or 24 h apart displayed different profiles of PrI uptake and S-100beta release, although neuronal loss and NSE release was similar in both paradigms. Cells receiving a subthreshold, low-level stretch (10%) repeated several times eventually stained with PrI. Cultures administered 10% stretch before mild injury released less S-100beta than mild injury alone, suggesting a preconditioning effect. Lastly, exogenous S-100beta applied to injured cultures decreased PrI uptake, implying a protective role. These results suggest cumulative damage is dependent on injury severity and inter-injury interval, and that neurons and glia react differently to various injury paradigms.