Inhibition of hair growth by subcutaneous injection of a sympathetic neurotoxin, 6-hydroxydopamine in neonatal mice.

The effects of a sympathetic neurotoxin, 6-hydroxydopamine (6-OHDA), on hair growth in neonatal mice were examined. Newborn mice were injected once subcutaneously in the mid-dorsal region with 6-OHDA (0.3 mg/g body weight) and bovine serum albumin (BSA) or with BSA only (controls) on day 0. By day 10, distinct areas of hairless skin were observed surrounding the sites treated with 6-OHDA. The areas of hairless skin were smaller at 15 days of age and were covered with hair by 20 days of age. Control sites injected with BSA only were indistinguishable from the surrounding skin at all ages examined. Microscopic and morphometrical analyses of skin obtained from the neonatal mice at various ages showed that the hairless skin in 6-OHDA-treated mice was thinner than the skin of control animals. The thinning of the skin and delay in hair growth induced by 6-OHDA treatment showed a significant difference from the skin of control animals injected with BSA only. Immunohistochemical experiments demonstrated that the administration of 6-OHDA had caused the complete depletion of tyrosine hydroxylase-immunoreactive fibers (sympathetic fibers) around blood vessels and piloerector muscles and in nerve bundles throughout the dermis and subcutaneous tissue. These findings indicate that the sympathetic neurons are associated with skin thickness and hair growth in neonatal mice.