Methylene Blue Dye Injection in Mouse Embryonic Urinary Tract: A Method To Assess the Congenital Obstruction in the Urinary Tract

To assess urinary tract obstruction, begin by immobilizing a perinatal mouse embryo in the supine position. Now, dissect the abdominal cavity of the embryo to locate a fully developed urinary tract, which consists of a pair of kidneys, ureters, and a common bladder with urethra.

Next, take an empty syringe connected to the tubing fitted with a microneedle. Fill the assembly with methylene blue solution - a deep blue tracking dye. Insert the microneedle into the lumen of the renal pelvis - a funnel-like dilated proximal end of the ureter in the kidney - and inject the dye solution.

Due to hydrostatic pressure, the dye flows from the renal pelvis of the kidneys through the ureter and finally accumulates into the lumen of the bladder. Repeat the dye injection procedure with the contralateral kidney to check the flow of dye from the corresponding side of the urinary tract.

Finally, use a stereomicroscope with a camera to image the urinary tract. Upon imaging, an unobstructed urinary tract shows a deeply stained bladder, while the abnormal urinary tract with obstruction restricts the free flow of the dye. Depending on the degree of blockage, a complete or partial absence of dye in the bladder lumen is observed.