Abstract
1. Using the method of Glenner et al. (8), we have demonstrate abundant monoamine oxidase in human skin.
2. In the epidermis, the reaction occurs in the cells of the malpighian layer. In all hair follicles, regardless of their states of activity, the wall of the pilosebaceous canal is intensely reactive. In growing follicles, the cells of the outer root sheath contain moderate enzyme activity particularly concentrated in the cells at the periphery, in the region above the bulb; small reactive granules are sparsely distributed in the cells of the dermal papilla. In quiescent follicles, there is moderate activity in the cells of the epidermal sac; the hair germ and the dermal papilla have a scant reaction. In the sebaceous glands, the duct and the undifferentiated cells at the periphery of the acini have a very strong reaction. Both apocrine and eccrine glands show strong enzyme activity.
3. Many cutaneous nerves contain monoamine oxidase. Reactive nerves form plexuses just beneath the epidermis, at the level of the sebaceous gland, and midway along the depth of the hair follicle; reactive nerves are also found around both eccrine and apocrine glands. Eccrine glands are surrounded by a richer bed of nerves than the apocrine glands are. The nerves to the arteries also contain the enzyme.
4. The localization of monoamine oxidase in human skin resembles that of succinic dehydrogenase; the cutaneous nerve fibers and the myoepithelial cells, which contain no succinic dehydrogenase, do, however, contain monoamine oxidase.
5. Many cutaneous nerve fibers, sensory and motor, seem to be reactive for both monoamine oxidase and cholinesterase, We do not know what this means in terms of physiology.