The TRP Channels Pkd2, NompC, and Trpm Act in Cold-Sensing Neurons to Mediate Unique Aversive Behaviors to Noxious Cold in Drosophila

Abstract

SUMMARY The basic mechanisms underlying noxious cold perception are not well understood. We developed Drosophila assays for noxious cold responses. Larvae respond to near-freezing temperatures via a mutually exclusive set of singular behaviors–in particular, a full body contraction (CT). Class III (CIII) multidendritic sensory neurons are specifically activated by cold and optogenetic activation of these neurons elicits CT. Blocking synaptic transmission in CIII neurons inhibits CT. Genetically, the transient receptor potential (TRP) channels Trpm, NompC, and Polycystic kidney disease 2 (Pkd2) are expressed in CIII neurons where each is required for CT. Misexpression of Pkd2 is sufficient to confer cold-responsiveness. The optogenetic activation level of multimodal CIII neurons determines behavioral output, and visualization of neuronal activity supports this conclusion. Coactivation of cold and heat responsive sensory neurons suggests that the cold-evoked response circuitry is dominant. Our Drosophila model will enable a sophisticated molecular genetic dissection of cold nociceptive genes and circuits.

Novel Assay for Cold Nociception in <em>Drosophila</em> Larvae

“…Using a fine, conical-tipped cold probe, we show that Drosophila larvae exhibit a set of cold-specific reactive behaviors, distinct from behaviors observed during normal locomotion, following gentle touch, or after harsh mechanical or high temperature stimuli 7,8,11 . The cold-specific behaviors include a robust full-body contraction (CT), a 45–90° raise of the posterior segments (PR) and a simultaneous raise of the anterior and posterior segments into a U-Shape (US).…”

“…Flies provide a sophisticated genetic toolkit and a simplified nervous system that allow for precise genetic and neuronal manipulation 1,2,3,4 to dissect the cellular and molecular bases of nociception 5,6,7 . Larvae are particularly useful for these analyses, given that behavioral assays for gentle touch 8,9,10 , noxious heat 11,12,13 and mechanical sensation of noxious stimuli 4,11 have already been established, and the transparent larval cuticle allows for live or fixed imaging of the epidermis and underlying sensory neurons.…”

“…Larvae are particularly useful for these analyses, given that behavioral assays for gentle touch 8,9,10 , noxious heat 11,12,13 and mechanical sensation of noxious stimuli 4,11 have already been established, and the transparent larval cuticle allows for live or fixed imaging of the epidermis and underlying sensory neurons. Recently, an assay for noxious cold has also been developed 7 , which we describe in more detail here.…”

Sensing the cold: TRP channels in thermal nociception

“…The present study 7 establishes a genetically tractable platform for elucidating conserved molecular bases of cold nociception and for revealing generalizable mechanisms underlying TRP channel mediated multimodality. The novel assays implemented in this work should also prove powerful tools in unraveling the neural circuit architecture by which complex multimodal stimuli are processed to drive behavioral selection.…”

“…In a recent study, 7 we identified the cellular basis for noxious cold detection, implicating the TRP channels Pkd2, NompC, and Trpm in regulating cold-evoked nociceptive behavioral responses. When challenged with temperatures at and below 14 C, Drosophila larvae execute a full-body contraction (CT) behavior along the head-to-tail axis.…”