[en] Gene imaging with radio-labeled antisense deoxyribonucleic acid (DNA) or peptide nucleic acid (PNA) is useful for detection of the expression of therapeutic gene in gene therapy in vivo. A delivery carrier is requisite for the imaging with antisense to transport the antisense to cell inside, since in general antisense does not across biological membrane. In the case of brain, there is another obstruction, the blood brain barrier (BBB), have to overcome. In the present study, surface-modified liposome and conjugate were prepared as tool to delivery antisense through the BBB. Poly-arginine peptides were bonded to the surface of conventional liposome. Although a small amount, this enabled the conventional liposome to enter the brain across the BBB after i.v. administration, while the conventional liposome is unable to do it in itself. In addition, antisense PNA was capacitated of entering the cultured hepatocytes in the presence of asialofetuin conjugated with oligonucleotides, and released in cytoplasm in vitro. This is very ideal for function of antisense since the binding of antisense to target may be weakened if without the release from delivery carrier. The brain-specific molecule as pilot is very import for targeting of delivery system. Our co-investigators found that microglia can migrate into brain across BBB from blood, while the migration toward other tissue was exiguous. The isolated plasma membrane from microglia could enter the brain similar to microglia, suggesting the brain-specific migration due to certain unknown molecule(s) on the surface of microglia. Identification of them will help us develop brain-specific delivery system. (author)