Such “myelinated nociceptors”
conduct in the Aβ range and respond to mechanical stimuli well into the nociceptive range, with a graded NU7441 research buy fashion and adaptive properties that resemble SAII units (Burgess and Perl, 1967, McIlwrath et al., 2007 and Woodbury and Koerber, 2003). Under normal conditions, myelinated nociceptors are also sensitive to innocuous mechanical stimuli, with von Frey thresholds as low as 0.07 mN. Some myelinated nociceptors also respond to noxious heat but are otherwise physiologically indistinguishable from their heat-insensitive counterparts (Treede et al., 1998). Because of their wide dynamic range, myelinated nociceptors are likely to serve both LTMR and nociceptive functions. Myelinated nociceptors can be found both in glabrous and hairy skin, although their anatomical morphologies NSC 683864 remain unknown. Proper identification and differentiation of Aβ-LTMRs versus Aβ-nociceptors will be critical to our understanding of pain states such as allodynia and hyperalgesia. Indeed, it has been suggested that tactile
allodynia after peripheral nerve injury is due to impulses carried along residual A fibers in the presence of dorsal horn sensitization (Campbell et al., 1988, LaMotte and Kapadia, 1993 and Woolf et al., 1992). However, it is possible that myelinated nociceptors mediate certain aspects of tactile allodynia, as they are quite sensitive to mechanical stimuli and are known to innervate lamina in the dorsal horn normally associated with nociception (Woodbury et al., 2008). Furthermore, decreases of mechanical thresholds in myelinated nociceptors after peripheral injury, as is the case with other nociceptors, may also contribute to pain states such as allodynia (Andrew and Greenspan, 1999 and Jankowski
et al., 2009). The anatomical substrate of our tactile perceptions lies in the intricate innervation patterns of physiologically distinct LTMRs and HTMRs and their respective end organs located in the skin. Each unique form, be it a rigid set of LTMR palisades surrounding hair follicles or a free nerve ending associated with keratinocytes, represents a distinct sensory unit that is uniquely tuned to a particular feature of our tactile world. Most of what we know of touch perception comes from studies whatever on glabrous skin of the primate hand or the rodent paw. Here, conceptual leaps in the interpretation of sensory neuron form and function have distilled the essence of touch perception into four main anatomical and physiological “channels,” which transduce mechanical signals into neural codes of rapidly adapting and slowly adapting impulses. Although there is no doubt that tactile information travels along these four channels, at least peripherally, the recently revealed patterns of hairy skin innervation urge us to consider a much more integrative view of touch perception.