PROJECT SUMMARY Detection of mechanical stimuli is crucial for organisms' development and survival. Discriminating between an innocuous mechanical stimulus and noxious mechanical force is vital to avoid tissue damage and resulting pain. Cutaneous mechanisms of mechanical stimulus detection have received considerable attention, however, the sensory neuron-specific mechanoreceptors underlying touch and pain are not fully understood. Piezo1 and Piezo2 ion channels are bona fide mechanotransduction cation channels expressed at various levels and tissues that comprise the peripheral nervous system, including keratinocytes and sensory neurons. While sensory neuron expression of Piezo2 is essential for peripheral sensation of tactile stimuli, relatively little is known about the role of its close relative, Piezo1. Despite early work suggesting dorsal root ganglia (DRG) sensory neurons display relatively robust Piezo2 expression and comparatively minimal Piezo1 expression, more recent evidence suggests that Piezo1 is expressed by sensory neurons and it can be mechanically and pharmacologically activated in these neurons. This suggests sensory neuron Piezo1 may be functionally important for detection of tactile and mechanical pain by the somatosensory system. Furthermore, while sensory neuron Piezo2 is implicated in mechanical allodynia, nothing is currently known about the contribution of sensory neuron Piezo1 to the mechanical allodynia or hyperalgesia characteristic of neuropathic or inflammatory pain conditions. In the experiments outlined in the current proposal, I will use evoked behavioral assays, patch clamp electrophysiology, and ex vivo skin-nerve recordings to determine the role Piezo1 plays in sensory neuron-mediated mechanosensation in naïve (non-injury) and pain (injury) contexts by using transgenic mice with sensory neuron specific deletion of Piezo1. In Aim 1, I will examine the contribution of sensory neuron-specific Piezo1 to mechanosensation (Aim 1A), to mechanically-evoked peripheral fiber responses (Aim 1B), and to DRG responses to mechanical stimuli (Aim 1C). Similar approaches will be used in Aim 2 to interrogate the role of Piezo1 in mechanical hypersensitivity induced by inflammation, using complete Freund's adjuvant, and peripheral neuropathy induced by spared tibial nerve injury. I will determine whether Piezo1 contributes to injury- induced mechanical allodynia and hyperalgesia (Aim 2A), and mechanical stimulus-induced sensitization of peripheral fibers (Aim 2B) and DRG sensory neurons (Aim 3C). These studies will ultimately reveal additional roles for mechanically-gated channels in tactile stimulus transduction. Overall, the proposed aims will reveal the contribution of sensory neuron Piezo1 to detection of mechanical stimuli in non-injury and injury conditions, potentially revealing new avenues for treatment of mechanical pain.