Patients with diabetes, cancer, complex regional pain syndrome, and other small fiber neuropathies often experience painful and maladaptive perception of innocuous thermal stimuli due to peripheral nerve damage. This unfortunate symptom of these disease states can severely impact the patient's daily life, and in the case of chemotherapy, can dangerously limit the ability to prescribe the effective dose. The molecular mechanisms of noxious heat perception is fairly well understood, but the same cannot be said for the basic mechanisms of noxious cold detection and processing, which is largely unexplored. Therefore, this proposal seeks to determine the genetic basis for noxious cold perception using the genetically tractable Drosophila as a model organism. Drosophila have already lent themselves as an advantageous model for discovering novel conserved genes required for noxious heat perception. In response to a locally applied high temperature probe, larvae exhibit a robust corkscrew-like rolling behavior, which is dependent on transient receptor potential (TRP) channels and a specific class of multidendritic sensory neurons under the larval epidermis. It has also been shown that this response is sensitized following tissue damage, requiring specific pathways. To assess the molecular and genetic basis for noxious cold, and to determine the extent of homology with noxious heat pathways, a novel low temperature probe was engineered to create an assay for cold nociception. The proposal's preliminary data shows Drosophila larva produce a set of behavioral responses that are distinct from the rolling response to noxious heat and harsh touch. These behaviors occur in approximately 75% of wild type larvae, and are consistent and reproducible. Based on previous work with noxious heat and the distinctly different behavioral responses observed to noxious cold stimuli, we hypothesize a separate, specific class of multidendritic sensory neurons and ion channels are required for the perception of noxious cold, and that this response is sensitized following tissue damage utilizing known pathways. The experiments proposed in this application will identify the specific cells and pathways required for cold nociception in Drosophila larvae, allowing further insight into the fiel of cold nociception and development of therapeutics.
This proposal takes advantage of a highly tractable genetic model, Drosophila, to answer critical questions about the genetic and molecular basis of noxious cold perception. Due to the prominent degree of homology in this system to vertebrates, and its proven usefulness in the past, the knowledge acquired from this project will guide future research to seek out better treatments for human patients with peripheral nerve damage, that cause thermal dysesthesias and aberrant perception of innocuous stimuli.