Adult organotypic brain slice preparation and biolistic transfection. A) The adult mouse brain were embedded in DMEM-agarose with penicillin/streptomycin. This DMEM-agarose matrix, readily suitable for handling, contains phenol red, hence the red coloration. This colour gradient also helps to see the OTBS cut by the vibroslicer. Scale bar: 10 mm. B) The OTBS seen in an empty well ready for transfection by biolistics. A red arrow indicates a rod support used to maintain distance and angle. C) Scaled model showing the height of the modified barrel over the OTBS. D) Distribution pattern of the scattered micro- and nanoparticles. The affected and chosen region of interest subsequently expresses the exogene . This biolistic transfection method is ideally suited for adult OTBS.