Figure 7.

Hypothetical scenario: human hair growth inhibition by substance P. Hypothetical scenario depicting direct and indirect pathways by which substance P may inhibit human hair growth in the context of psychoemotional stress and neurogenic inflammation. On the left an anagen VI hair bulb is depicted. Gray cells with black membrane show location of proliferating Ki-67⁺ cells in the hair matrix that also express weak NK1 and TrkA immunoreactivity. On the right a regressing (mid catagen) hair bulb is depicted. Light gray cells indicate rarified proliferating Ki-67⁺ cells that also express NGF and some of which express p75NTR and show ectopic MHC I expression (gray cells with black membrane). Close by a nerve fiber in contact with degranulated mast cells and some monocytes are shown. Note that NK1, TrkA, p75NTR, and MHCII immunoreactivity outside the proliferative compartment are not schematized for easier comprehensibility. MKC, matrix keratinocyte.