Receptors, cells and circuits involved in pruritus of systemic disorders.

Pruritus is a sensory phenomenon accompanying a broad range of systemic disorders including hematologic and lymphoproliferative disorders, metabolic and endocrine diseases, solid tumours, and infectious diseases. The molecular mechanisms involved in itch sensation remain enigmatic in most of these diseases. However, from studies in patients and animal models a large number of mediators and receptors responsible for scratching behaviour have been identified in recent years. New insights into the interplay between neuronal and non-neuronal cells in the initiation, modulation and sensitization of itch sensation have been acquired. This review highlights the current knowledge of the molecular mechanism involved in pruritus of systemic disorders and summarizes the signalling pathways of biogenic amines, neuropeptides, proteases, eicosanoids, cytokines, opioids, endocannabinoids, neurotrophins, phospholipids and other signalling molecules participating in pruritus.