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  1. Introduction.
  2. Neuropeptides.
  3. Receptors.
  4. Substance P.
  5. Catecholamines.
  6. Neuropeptide Y.
  7. Adenosine triphosphate.
  8. Neurogenic inflammation.
  9. Cutaneous/Dermatologic diseases.
    1. Urticaria.
    2. Pruritus.
    3. Atopic dermatitis.
    4. Psoriasis.
    5. Vitiligo vulgaris.
    6. Allergic contact dermatitis.
    7. Ultraviolet radiation.
  10. Conclusion.

Human skin consists of a sophisticated network of nerve fibers and specialized sensory structures to transduce sensations of touch, vibration, temperature, and pain. Nerve fibers have dual functions: to transmit afferent sensory impulses to the central nervous system and to secrete mediators into the local environment. While many of these mediators are polypeptides (called neuropeptides), others are nonpeptide factors. These factors affect various biologic processes including inflammation, immunity, wound healing, and aging. Cutaneous neurobiology is an expanding field of research with increasing clinical implications. The presence of neuropeptide receptors on epidermal and dermal cells and the close anatomic relationship of nerve fibers with immune and nonimmune cells demonstrate the direct link between the sensory nervous system and the largest organ system of the human body, the skin. Neuropeptides (NPs) are a heterogeneous group of polypeptides ranging from 2 to greater than 40 amino acids in size. There are over 50 identified neuropeptides, 11 of which are found in human skin. Neuropeptides are released in response to a range of stimuli from pain and temperature to irritation in order to mediate diverse biologic processes related to injury, inflammation, infection, and wound healing.

[...] Vitiligo Vulgaris Vitiligo is a depigmenting disorder often presenting in a symmetric or segmental distribution. There are changes in neuropeptides distribution in affected skin. An increase in NPY, CGRP, and SP has been demonstrated, whereas no changes in VIP was observed, supporting the concept that neuropeptides are involved in the pathogenesis of vitiligo. Alopecia Areata Alopecia areata is characterized by nonscarring patches of hair loss. The pathogenesis is complex and unclear, as immunologic, genetic, environmental, and psychological factors are implicated; however, stressful life events may trigger or exacerbate the disease. [...]

[...] fibers; however, evidence exists that epidermal and dermal cells also produce neuropeptides and neurohormones. These cells include fibroblasts, keratinocytes, Langerhans' cells, macrophages, mast cells, melanocytes, endothelial cells, Merkel cells, and leukocytes. The distribution of neuropeptides varies depending on the body site. High levels of SP, NKA, and CGRP are found in areas with the greatest tactile sensation. Intermediate levels are found in the neck and face, whereas the lowest levels are present in the groin, arm, and thigh. Levels of VIP and peptide histidine methionine (PHM) are also highest in axillary skin, suggesting their role in axillary eccrine sweat production. [...]

[...] Neurogenic Inflammation Cutaneous neurogenic inflammation implies the role of nerves in cutaneous inflammation. The neuropeptides secreted by sensory nerves evoke an inflammatory response referred to as neurogenic inflammation. The axon- reflex model implies that tissue injury triggers a signal to the dorsal root ganglion toward the CNS (orthodromic response) with return of the signal from branch points in the reverse direction to exert effects at the local level. The orthodromic response transmits pain, whereas the antidromic response leads to the release of neuropeptides in the innervated tissue. [...]

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