Abstract: The dentate gyrus of the hippocampus is a plastic structure that displays modifications at different levels in response to positive stimuli as well as to negative conditions such as brain damage. The latter involves global alterations, making understanding plastic responses triggered by local damage difficult. One key feature of the dentate gyrus is that it contains a well-defined neurogenic niche, the subgranular zone, and beyond neurogenesis, newly born granule cells may maintain a “young” phenotype throughout life, adding to the plastic nature of the structure. Here, we present a novel experimental model of local brain damage in organotypic entorhino-hippocampal cultures that results in the activation of adjacent newly born granule cells. A small piece of filter paper was placed on the surface of the granule cell layer of the dentate gyrus, which evoked a foreign body reaction of astrocytes, along with the activation of local young neurons expressing doublecortin. Forty-eight hours after foreign body placement, the number of doublecortin-immunoreactive cells increased in the subgranular zone in the direct vicinity of the foreign body, whereas overall increased doublecortin immunoreactivity was observed in the granule cell layer and molecular layer of the dentate gyrus. Foreign body placement in the pyramidal layer of the CA1 region evoked a comparable local astroglial reaction but did not lead to an increase in doublecortin-immunoreactive in either the CA1 region or the adjacent dentate gyrus. Seven days after foreign body placement in the dentate gyrus, the increase in doublecortin-immunoreactivity was no longer observed, indicating the transient activation of young cells. However, 7 days after foreign body placement, the number of doublecortin-immunoreactive granule cells coimmunoreactive for calbindin was lower than that under the control conditions. As calbindin is a marker for mature granule cells, this result suggests that activated young cells remain at a more immature stage following foreign body placement. Live imaging of retrovirally green fluorescent protein–labeled newly born granule cells revealed the orientation and growth of their dendrites toward the foreign body placement. This novel experimental model of foreign body placement in organotypic entorhino-hippocampal cultures could serve as a valuable tool for studying both glial reactivity and neuronal plasticity, specifically of newly born neurons under controlled in vitro conditions.

Key words: astrocyte, brain plasticity, dendritic plasticity, dentate gyrus, focal brain injury, hippocampus, neuroplasticity, neurorepair, newborn granule cells, regeneration, reorganization