Temporal characterization of microglia, IL-1 beta-like immunoreactivity and astrocytes in the dentate gyrus of hippocampal organotypic slice cultures.

These studies demonstrate that murine hippocampal slice cultures possess neural-immune elements that show responses parallel to comparable in vivo models of neural-immune activation. Using immunocytochemical techniques, this study characterized the phenotypes of specific glial elements and the expression of the cytokine, interleukin-1 (IL-1 beta), in the hippocampal dentate gyrus over a period of 10 days in vitro (DIV). Preparation of organotypic slice cultures of neonatal mouse hippocampus produced cellular damage including axotomy of afferent fibers within the molecular layer of the dentate gyrus. This form of lesion-induced injury caused activation of neural-immune elements in the slice cultures. Staining with the microglial specific biotinylated Griffonia simplicifolia B4-isolectin revealed reactive microglia were most prevalent at 2 DIV and decreased in number from 4 to 10 DIV, whereas the initial population of resting microglia at 2 DIV increased approximately four-fold from 4 to 10 DIV. The presence of a round IL-1 beta-like immunophenotype closely paralleled the temporal and spatial distribution of the reactive form of microglia observed in the dentate gyrus. In addition, between 4 and 10 DIV, some IL-1 beta-like immunoreactive cells exhibited a stellate-like morphology with numerous branching processes, similar to resting microglia. At 2 DIV astrocytes showed minimal labeling with antibodies directed against glial fibrillary acidic protein (GFAP), while from 4 to 10 DIV, a dramatic hypertrophic astrocytic response occurred, resulting in a gliotic scar forming over the entire dentate gyrus. We conclude that neural-immune activation in the hippocampal organotypic slice culture preparation closely parallels similar responses observed in vivo and thus slice cultures represent an excellent model for further studies of neural-immune interactions resulting from lesion-induced injury in the central nervous system.