Determining the function of medium to large diameter sensory neurons in paclitaxel-induced pain via large-scale in vivo DRG imaging

Paclitaxel-induced peripheral neuropathy (PIPN) is a common painful treatment side effect that affects millions of cancer patients. Currently there are no adequate treatments for this debilitating neuropathy, thus studies are needed to understand the neuronal and molecular changes that lead to PIPN. Most PIPN studies utilize traditional cell culture systems and single unit electrophysiological recordings, methods that cannot capture the full dynamics of the intact peripheral nervous system. Our lab recently developed a novel whole dorsal root ganglia (DRG) in vivo imaging technology that can monitor activity of all DRG neurons simultaneously. Using this new technology, we found medium to large DRG neurons become hyperactive after the onset of PIPN. These neurons are significantly hypersensitive to mechanical and cold stimuli, but not heat. Our proposal combines in vivo imaging with genetic labeling strategies to explore the function of medium to large diameter neuron subtypes in paclitaxel induced pain (PIP). We hypothesize that paclitaxel selectively affects specific medium to large diameter neuronal populations, which leads to painful mechanical and cold hypersensitivity. Aim 1 will determine the neuronal populations and molecular mechanisms for mechanical and spontaneous pain in PIP. We will use cre-dependent mouse lines to specifically delete and activate neurons expressing lowthreshold mechanoreceptors (TrkB+ Aδ- and TrkB+ Aβ RA1-LTMRs) and mechanoreceptors (Bmpr1b+ and Smr2+ A-MRs). Behavior and in vivo imaging approaches will determine the roles of these subpopulations in PIP. We will examine the role of gap junctions in paclitaxel treatment-induced mechanical hypersensitivity. Genetic and pharmacological approaches will study how blocking gap junction-mediated neuron coupling reduces mechanical pain and DRG neuronal activation. Our Pirt-Cre; R26-CAG-lsl-CaMPARI2 mouse studies will characterize the subpopulation of medium to large diameter DRG neurons involved in spontaneous pain after paclitaxel dosing. Aim 2 will identify novel cold-sensing neuronal populations hyperactivated in PIP. The one verified cold receptor TRPM8 is expressed on small diameter DRG neurons. Our preliminary data showed that in PIP, medium diameter neurons hyperactivated by cold do not respond to the canonical TRPM8 agonist menthol. We recently showed that a novel cold receptor, GluK2, is expressed in medium diameter DRG neurons. We hypothesize that GluK2 is involved in paclitaxel induced cold pain. We will utilize a new GluK2-cre reporter mouse to examine the function of this newly identified cold-sensing population. We will analyze the transcriptome and electrophysiological properties of these neurons to identify molecular targets suitable for pharmacology. Together, our proposed studies will dissect the crucial roles that novel medium to large diameter neuron subtypes play in transmitting mechanical pain from innocuous touch and noxious pinch, cold and spontaneous pain in PIP. These impactful studies could lead to discovery of novel pharmacological targets for specific populations of sensory neurons to treat PIP patients’ intolerable mechanical and cold hypersensitivities and spontaneous pain.