An open cremaster muscle preparation for the study of blood vessels by in vivo microscopy

Abstract

A survey is made of the various approaches employed for the study of the microcirculation in striated muscle (cremaster) by in vivo microscopy in the rat, and the technique for opening the muscle pouch is described. When opened and extended the rat's cremaster, of 2.7 ± 0.4-cm diam and 175 ± 15 μm in thick ness, can be transilluminated in toto, and the branches of cremasteric artery and vein visualized to their final ramifications. It also allowed direct measurements of dynamic changes of lumen and wall of the small blood vessels to be made at high power and maximum resolution of the electrooptical image on the television screen. A platform microtensor device sustains the spread muscle on the stage of the microscope, and allows quantitative evaluation of microcirculatory variables to be made at known amounts of stretch of the host tissue. Radial spreading of the tissue with a stretch force equivalent to < 180 mg, alters neither size nor reactivity of muscular precapillary vessels, and no change of blood in capillary occurred from that seen in exposed, unopened cremaster. The method was applied to the mouse. Cremaster muscle in this rodent measured 1.7 ± 5 mm in diameter, and 98.5 ± 11.0 μm in thickness. The method for striated cremaster muscle, experimental set up and optics provide a clear field for observing the smallest blood vessels in this tissue, for over more than 2 hr, without significant changes in dynamic activity and flow characteristics.