However, unlike RA-LTMRs that associate with guard and awl/auchene follicles of the mouse, Aδ-LTMR lanceolate endings are found around awl/auchene and zigzag, but not guard hair follicles (Li et al., 2011) (Figure 1B). C-LTMRs. Though C fibers are often associated with painful stimuli, mechanoreceptors with conduction velocities within the C fiber range were described in the cat as early as 1939

by Ingve Zotterman (1939) and suggested to be associated with “tickling” sensations. Subsequent research on C-LTMRs indeed established that not all cutaneous sensory receptors http://www.selleckchem.com/products/KU-55933.html with afferent C fibers are concerned with relaying noxious information (Douglas and Ritchie, 1957, Iggo, 1960 and Iggo and Kornhuber, 1977). In addition, since sensory C fibers are three to four times more numerous than A fibers, C-LTMRs far outnumber the myelinated fibers innervating skin (Li et al., 2011). Like Aδ-LTMRs, C-LTMRs are exquisitely sensitive to skin indentation but are maximally activated by stimuli that move slowly across their receptive

field and are thus suggested to be “caress click here detectors.” The C-LTMR physiological profile is unique among hairy skin LTMRs. Most notably, they exhibit an intermediately adapting property, with a modest sustained discharge during a maintained stimulus (Table 1). Unlike other hairy skin LTMRs, C-LTMRs also show a high incidence of after-discharge, even several seconds after the stimulus is removed. The shape of their action potentials is characteristic of C fibers, with broad waveforms displaying a prominent hump on the falling phase. As with Aδ-LTMRs, C-LTMRs are sensitive to rapid cooling, but not warming, of the skin; however, it is unclear whether the temperatures to which these receptors respond to are physiologically relevant

for the behaving animal. One of the most striking features of C-LTMR responses is that they are only found in hairy skin. Though less common in nonhuman primate skin, C-LTMRs are present in human hairy skin and are speculated to play a role in mediating “emotional touch” (Kumazawa and many Perl, 1977, Löken et al., 2009, McGlone et al., 2007 and Vallbo et al., 1993). Indeed, in humans lacking large myelinated fibers, activation of C-LTMRs is correlated with a sensation of pleasantness often associated with activation of the insular but not the somatosensory cortex (Björnsdotter et al., 2009 and Olausson et al., 2002). The peripheral and central anatomy of C-LTMRs was largely unknown until recent studies in the mouse postulated that they may have several anatomical forms in hairy skin. Postrecording intracellular labeling of C-LTMRs identified in ex vivo skin nerve recordings revealed that C-LTMRs express tyrosine hydroxylase (TH). By utilizing a CreER knocked into the TH locus, Li et al.