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 axonal terminals in the periphery and project axons centrally to the spinal cord to transmit tactile information. Current understanding of LTMR development and organization comes from fixed tissues that cannot reveal the dynamic and temporal processes of axonal wiring and remodeling. Here, a two-photon imaging method is presented for visualizing LTMR axon morphology in the mouse forepaw during development and in adults. Two-photon microscopy can achieve high-resolution imaging within intact skin, enabling repeated imaging of the same axon terminals across postnatal time points. Two-photon imaging can be combined with new mouse genetic tools to reveal axon development with subtype-specificity. Chronic imaging of LTMRs enables studies of circuit assembly and repair following injury. These approaches provide an in vivo system that will provide new insights into the cellular mechanisms that regulate somatosensory axon development and regeneration.