INTRODUCTIONThis protocol describes how to dissect, assemble, and cultivate mouse embryonic (E) brain tissue from age E11.5 to E18.5 (days) for organotypic slice culture. These preparations can be used for a variety of assays and studies including coculture of different brain regions, cell migration assays, axon guidance assays, and DNA electroporation experiments. During electroporation, an electric current is applied to the surface of a specific target area of the brain slice in order to open holes in the plasma membrane and introduce a plasmid of coding DNA. The floating slice-on-membrane construct helps to preserve the structural integrity of the brain slices, while maintaining easy experimental access and optimal viability. Experiments can be monitored in living slices (e.g., with confocal imaging), and further studies can be completed using slices that have been fixed and cryosectioned at the end of the experiment. Any region of embryonic brain or spinal tissue can be used in this protocol.