The different substances that elicit itch upon intracutaneous injection (injection within the skin) elicit only pain when injected subcutaneously (beneath the skin).Itch is readily abolished in skin areas treated with nociceptor excitotoxin capsaicin but remains unchanged in skin areas rendered touch insensitive by pretreatment with anti-inflammatory saponins. Although experimentally induced itch can still be perceived under a complete A-fiber conduction block, it is significantly diminished. Overall, itch sensation is mediated by A-delta and C nociceptors located in the uppermost layer of the skin. Molecular diversity of itch transmitting primary afferents
Using single-cell mRNA sequencing, sensory-modality specific primary afferent have been molecularly defined into clusters based on gene expression patterns. Here, 11 sub clusters were detected; NF1-3, transmitting innocuous nociceptive information; NF4-5, which transmit proprioceptive information; NP1-3, transmitting itch information; PEP1-2, nociceptive information and TH, which is involved in pleasant touch, The pruriceptive NP1-3 were shown to express genes related to histaminergic and non-histaminergic signaling, where NF1 expresses genes responding to lysophosphatidic acid (Lpar3 and Lpar5), NP2 chloroquine-responsive genes (Mrgpra3 and Mrgprx1), whereas NP3 expresses neuropeptides Nppb and Sst as well as genes involved in inflammatory itch (Il31ra, Osmr and Crystrl2). The histamine receptor gene Hrh1 was found in NP2 and NP3, suggesting that histaminergic itch is transmitted by both these pruriceptive sub clusters. The spinal itch pathway
After the pruriceptive primary afferent has been activated, the signal is transmitted from the skin into the spinal dorsal horn.
Median raphe cysts are a cutaneous condition of the penis due to developmental defects near the glans. : 682

See also
Cutaneous columnar cyst
List of cutaneous conditions


== References ==