Co-transfection of SCG neurons using PEI. Neurons cultured from perinatal rat SCG were transfected with 1 μg LacZ, 1 μg EGFP, and 5 μg PEI on the fifth day in vitro. Three days later, cells were fixed and immunostained using a monoclonal antibody to β-galactosidase with a rhodamine-conjugated secondary antibody. Panel (A) shows a phase-contrast image of two neurons stuck together. The neuron on the left in (A) is expressing β-galactosidase (B) as well as EGFP (C). Scale bar = 20 m.