Immunohistochemical localization of neurotrophin receptor proteins in human skin.

The target organs of neurotrophin-dependent sympathetic and sensory neurons, including the skin, synthesize and release neurotrophins, primarily NGF. Neurotrophins undergo retrograde axonal transport, and exert specific function in the perikarya of the responsive neurons. Moreover, evidence exists for an autocrine and/or paracrine function of neurotrophins in the skin. This study analyses the immunohistochemical localization of low (gp75) and high-affinity (gp140 trkA, gp145trkB and gp145trkC) neurotrophin receptor proteins in the human glabrous skin. We consider that the expression of neurotrophin receptors may be indicative of neurotrophin activity. Specific gp75 and gp140trkA-like immunoreactivity (IR) were observed highly co-localized in (1) epidermis, primarily in the basal keratinocytes; 2) sweat glands; (3) blood vessel walls, mainly in the muscular layer; (4) Schwann and perineurial cells of nerve trunks; (5) periaxonic cells forming sensory nerve formations (Meissner's and Pacini's corpuscles); (6) large axons of nerve bundles and of sensory corpuscles; gp145trkB-like and gp145trkC-like were found labelling nerve fibers and sensory nerve formations, as well as blood vessels and sweat glands, but not epidermic cells. The results suggest that, in addition to the well known neurotrophic functions, neurotrophins may also regulate unknown functions in non-nervous cutaneous cells, which are targets for neurotrophin-dependent sympathetic and sensory neurons.