Immunohistochemical localization of the high‐affinity NGF receptor (gp 140‐trkA) in the adult human dorsal root and sympathetic ganglia and in the nerves and sensory corpuscles supplying digital skin

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Abstract
Background: Nerve growth factor (NGF) is produced in target issues of sympathetic and neural‐crest derived sensory neurons, including skin, to provide them trophic support. The biological effects of NGF on responsive cells are mediated by specific high‐affinity receptors. Recently, a protein tyrosine kinase of ≃ 140 kDa molecular weight, encoded by the proto‐oncogene trkA, has been identified as the high‐affinity NGF receptor (gp140‐trkA). The present work was undertaken to study the localization of gp140‐trkA‐like immunoreactivity (IR) in human peripheral ganglia (sympathetic and dorsal root ganglia), and in glabrous skin.Methods: Lumbar dorsal root ganglia, para‐ and prevertebral sympathetic ganglia, and digital glabrous skin were studied immunohistochemically using a rabbit anti‐gp140‐trkA polyclonal antibody. In order to accurately establish the localization of gp140‐trkA IR, the neurofilament proteins and S‐100 protein were studied in parallel in: (1) sensory and sympathetic ganglia, to label neuron cell bodies and satellite or supporting cells, respectively; (2) human skin, to label axons, Schwann and related cells within nerves and sensory corpuscles. Moreover, a quantitative study (neuron size, intensity of immunostaining) was carried out on sympathetic and dorsal root ganglia neuron cell bodies.Results: A specific gp140‐trkA‐like IR was found in: (1) a subpopulation (65%) of primary sensory neuron cell bodies, including most of the largesized ones but also small‐ and intermediate‐sized ones; (2) most of sympathetic neuron cell bodies (82%); (3) theineurial cell, Schwann cells, and large axons of the nerve trunks supplying digital skin; (4) the lamellar cells of Meissner corpuscles; (5) the central axon, inner‐core, outer‐core, and capsule of Pacinian corpuscles. In addition, the occurrence of gp140‐trkA‐like IR was observed in some non‐nervous tissues of the skin, including epidermis (mainly in the basal layer), sweat glands, and arterial blood vessels.Conclusions: Present results provide evidence for the localization of gp140‐trkA‐like IR in: (1) nerve cells which are known to be NGF‐responsive, and (2) non‐nervous cutaneous tissues which are innervated by NGF‐dependent peripheral neruons. These findings suggest that, in addition to the well‐established role of NGF on sensory and sympathetic neurons, this neurotrophin may be able to regulate some other functions on non‐nervous cell which are targets for NGF‐dependent peripheral neurons.