Intraductal Injection into the Mouse Mammary Gland

The mammary epithelium is continuous with the skin through a teat canal leading to a single primary duct in the mouse. Using fire-polished micropipettes 60 to 75 μm in diameter, it is possible to inject any desired substance directly through the teat into the lumen of the mammary gland. If the primary duct of the gland is exposed surgically, hypodermic needles can also be used for injection. Both techniques can be used to investigate the state of tight junctions in the mammary gland by examining transepithelial movement of radioactive sugars or fluorescent-labeled proteins. The intraductal or up-the-teat injection of adenoviral and plasmid vectors provides a convenient means of altering gene expression in the luminal epithelium. Finally, injected fluorescent probes as well as adenovirus-transduced green fluorescent protein can be directly visualized in the mammary gland in the living mouse by using confocal microscopy.