Intravital Two-Photon Imaging of Touch Sensory Axon Morphology in Mouse Skin
Low-threshold mechanoreceptors (LTMRs) are somatosensory neurons that detect innocuous light touch stimuli such as vibration, hair deflection, and pressure. They form subtype-specific terminals in the periphery and project axons centrally to the spinal cord to transmit tactile information. Current understanding about LTMR development and organization comes from fixed-tissue studies that cannot reveal the dynamic and temporal processes of neuronal wiring and remodeling. Here, we demonstrate a two-photon imaging method for visualizing LTMR axon morphology in the mouse right forepaw during development and in young adults. Two-photon microscopy can achieve high-resolution imaging within intact skin, allowing repeated imaging of the same axon terminals over postnatal timepoints. These approaches provide an in vivo system for studying the cellular mechanisms that regulate LTMR patterning and plasticity. Its application to longitudinal analyses will enable the observation of the assembly of touch circuits and their repair following injury. This technique may provide essential information about somatosensory axon structure and function in the skin.