Molecular genetic visualization of a rare subset of unmyelinated sensory neurons that may detect gentle touch.

C-fiber tactile afferents are a subpopulation of unmyelinated cutaneous sensory neurons activated by gentle stroking. Using a genetically encoded tracer, we found that Mas-related G protein-coupled receptor B4 marks a rare subpopulation of unmyelinated, nonpeptidergic sensory fibers that exclusively innervate hairy skin. These fibers terminate in large arborizations similar in size and distribution to C-fiber tactile afferent receptive fields, suggesting that MrgprB4 may provide genetic access to these elusive neurons in mice.