To begin, take an electronic Vernier caliper, position its outer jaw at the midpoint of the ear's outer edge, and extend it into the ear canal. Measure and record the thickness at two thirds and one half points along the line. Then, tilt the rat's head to one side, orienting the ear upwards.
Apply 50 microliters of oleic acid evenly to both the ventral and dorsal sides of the ear, once daily, for 25 days. Using a one milliliter syringe equipped with a 34 or 36 gauge needle, inject 50 microliters of cutibacterium acnes suspension intradermally into the ventral surface of the ear. On day 25, measure and record the thickness of the ears.
After cutting the ears off the euthanized rat, drill fixed size holes in the ears using an eight millimeter ring drill. After preparing and staining the ear sections, observe them under a light microscope. Record the pathological changes for follow-up evaluation by a pathologist, and assign scores to these changes according to the table shown here.
The ears in the oleic acid and oleic acid with cutibacterium acnes groups showed thickening, induration, erythema, scales, and comedones with occasional bleeding due to scratching. Histopathological analysis revealed parakeratosis, hyperkeratosis and hypertrophy in the oleic acid and oleic acid with cutibacterium acnes groups. Pathological scoring indicated increased severity in these groups compared to the control group.
Immunohistochemistry showed higher expression of TNF alpha in the dermis of the cutibacterium acnes, and oleic acid with cutibacterium acnes groups.
