Visualization of the Cutaneous Axonal Endings of CLTMs
Affective touch is hypothesized to be driven by unmyelinated low-threshold mechanoreceptors that are often abbreviated as CLTMs in animals and CTs in humans. Despite numerous neurophysiological studies, morphological identification of CLTMs has been reported in only a few animal studies, but with contrasting data.
In the first mouse study, CLTMs were identified with a rare subpopulation of unmyelinated sensory fibers denominated Mas-related G-protein-coupled receptor B4 (MrgprB4) which encircled the neck of hair follicles. By contrast, a different mouse study supported the correspondence of CLTMs with tyrosine hydroxylase (TH) positive fibers which were found to form longitudinal lanceolate endings associated with hair follicles. A morphological study of CT skin endings in humans is needed to explain species-related difference or to define if CLTMs described in animals represent only one class of human CTs.
KeywordsC-tactile unmyelinated nerve afferents Affective touch MrgprB4 TH Microneurography Hair follicle
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