Fig. 4.

Sympathetic nerves innervating HFs are required for light-induced anagen entry. (A) Effect of parabiosis. Light stimulation induced anagen only in the irradiated mouse (blue arrowhead) but not in the paired nonirradiated mouse. Similar results were obtained in five independent experiments. (B) Compressed immunostaining images of thick (34-μm) sections. (Left) In telogen, sympathetic nerves were in close proximity to bulge (BG) and secondary hair germ (SHG) areas before looping around arrector pili muscles. (Right) 6-OHDA treatment disrupted sympathetic innervation in all HFs examined (n = 30). DP, dermal papilla; K5, keratin 5; TH, tyrosine hydroxylase. (Scale bar, 50 μm.) (C) Effect of pharmacological sympathectomy with 6-OHDA. 6-OHDA treatment inhibited light-triggered anagen entry. *P < 0.05 (n = 10).