In utero electroporation-mediated gene transfer system. Embryos are visualized through the uterus and plasmid DNA was injected into the left cerebral ventricle of each embryo through a glass capillary. A fine tungsten negative electrode and a platinum positive electrode were inserted into the left and right hemispheres, respectively, and a series of three square-wave current pulses were delivered, resulting in gene transfection into the medial wall of the left hemisphere. After 24 hours the electroporation was performed, localized ectopic gene expression is shown only on one side of the brain (right bottom).