Abstract
BackgroundPolymodal, nociceptive sensory neurons are key cellular elements of the way animals sense aversive and painful stimuli. In Caenorhabditis elegans, the polymodal nociceptive ASH sensory neurons detect aversive stimuli and release glutamate to generate avoidance responses. They are thus useful models for the nociceptive neurons of mammals. While several molecules affecting signal generation and transduction in ASH have been identified, less is known about transmission of the signal from ASH to downstream neurons and about the molecules involved in its modulation.ResultsWe discovered that the regulator of G protein signalling (RGS) protein, EGL-10, is required for appropriate avoidance responses to noxious stimuli sensed by ASH. As it does for other behaviours in which it is also involved, egl-10 interacts genetically with the Go/iα protein GOA-1, the Gqα protein EGL-30 and the RGS EAT-16. Genetic, behavioural and Ca2+ imaging analyses of ASH neurons in live animals demonstrate that, within ASH, EGL-10 and GOA-1 act downstream of stimulus-evoked signal transduction and of the main transduction channel OSM-9. EGL-30 instead appears to act upstream by regulating Ca2+ transients in response to aversive stimuli. Analysis of the delay in the avoidance response, of the frequency of spontaneous inversions and of the genetic interaction with the diacylglycerol kinase gene, dgk-1, indicate that EGL-10 and GOA-1 do not affect signal transduction and neuronal depolarization in response to aversive stimuli but act in ASH to modulate downstream transmission of the signal.ConclusionsThe ASH polymodal nociceptive sensory neurons can be modulated not only in their capacity to detect stimuli but also in the efficiency with which they respond to them. The Gα and RGS molecules studied in this work are conserved in evolution and, for each of them, mammalian orthologs can be identified. The discovery of their role in the modulation of signal transduction and signal transmission of nociceptors may help us to understand how pain is generated and how its control can go astray (such as chronic pain) and may suggest new pain control therapies.
Highlights
Polymodal, nociceptive sensory neurons are key cellular elements of the way animals sense aversive and painful stimuli
Loss of egl-10 function affects the response to aversive stimuli egl-10 encodes a conserved regulator of G protein signalling (RGS) protein involved in egg-laying and locomotion behaviour, and loss of its function causes defective egg-laying and sluggish movement [13]
For avoidance, the function of egl-10 is required in ASH, we introduced in egl-10 mutants the wild-type egl-10 cDNA and expressed it in the ASH neurons under the sra-6 promoter
Summary
Nociceptive sensory neurons are key cellular elements of the way animals sense aversive and painful stimuli. In Caenorhabditis elegans, the polymodal nociceptive ASH sensory neurons detect aversive stimuli and release glutamate to generate avoidance responses. They are useful models for the nociceptive neurons of mammals. While several molecules affecting signal generation and transduction in ASH have been identified, less is known about transmission of the signal from ASH to downstream neurons and about the molecules involved in its modulation. In Caenorhabditis elegans, the two ciliated ASH sensory neurons play a major role in the detection of aversive stimuli and the generation of avoidance responses. Less is known about the mechanisms and molecules that in ASH modulate the transmission of the signal to the downstream interneurons. Exceptions are nlp-3-encoded peptides and their receptor, NPR-17, that mediate serotonin-dependent stimulation of ASH aversive response to dilute octanol [11] and the EGL-3 proconvertase, which appears to modulate ASH transmission but functions in the downstream interneurons and presumably affects ASH through secreted neuropeptides [12]
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