Method for in vivo microscopy of the cutaneous microcirculation of the hairless mouse ear

Abstract

The transilluminated, intact ear of the homozygous (hr/hr) hairless mouse was used as an in vivo preparation of the cutaneous microcirculation. The average thickness of the ear is 300 μm. The ear is composed of two full-thickness layers of skin separated by a thin supporting skeleton of elastic cartilage. With the exception of sweat glands, the skin of the hairless mouse ear closely resembles human skin. A subpapillary vascular network contained precapillary arterioles, capillary loops, and postcapillary venules. The remaining vessels were located in a subdermal vascular network. Arteriovenous anastomoses from 10- to 12-μm feeding arterioles were observed with intermittent blood flow. These anastomoses supplied a branching network of capillaries. The hairless mouse ear was easily prepared for study, requiring only light anesthesia and restraints. The observation chamber used was designed for use within the slide holder on a standard laboratory microscope stage. The observed ear was gently outstretched and placed within a well filled with sterile water at room temperature. The skin microcirculation was observed with a water-immersion objective in this manner or the well was sealed by a waterproof putty and a micro-coverglass and observations were made with long-working-distance objectives. The temperature of the water bathing the ear was continuously monitored. A video camera and videotape recorder were used and enable optical methods of blood flow measurement to be performed. Inside-vessel-diameter measurements were made with a video analyzer. The transilluminated hairless mouse ear provided a simple, inexpensive, and reproducible in vivo model to study the microcirculation of intact mammalian skin.