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In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP

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  • Ref In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP

    http://advances.sciencemag.org/conte.../e1600990.full

    Abstract

    Mechanistic insights into pain pathways are essential for a rational approach to treating this vast and increasing clinical problem. Sensory neurons that respond to tissue damage (nociceptors) may evoke pain sensations and are typically classified on the basis of action potential velocity. Electrophysiological studies have suggested that most of the C-fiber nociceptors are polymodal, responding to a variety of insults. In contrast, gene deletion studies in the sensory neurons of transgenic mice have frequently resulted in modality-specific deficits. We have used an in vivo imaging approach using the genetically encoded fluorescent calcium indicator GCaMP to study the activity of dorsal root ganglion sensory neurons in live animals challenged with painful stimuli. Using this approach, we can visualize spatially distinct neuronal responses and find that >85% of responsive dorsal root ganglion neurons are modality-specific, responding to either noxious mechanical, cold, or heat stimuli. These observations are mirrored in behavioral studies of transgenic mice. For example, deleting sodium channel Nav1.8 silences mechanical- but not heat-sensing sensory neurons, consistent with behavioral deficits. In contrast, primary cultures of axotomized sensory neurons show high levels of polymodality. After intraplantar treatment with prostaglandin E2, neurons in vivo respond more intensely to noxious thermal and mechanical stimuli, and additional neurons (silent nociceptors) are unmasked. Together, these studies define polymodality as an infrequent feature of nociceptive neurons in normal animals.
    Jo Bowyer
    Chartered Physiotherapist Registered Osteopath.
    "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

  • #2
    Most DRG Sensory Neurons Are Modality-Specific, Not Polymodal

    http://www.painresearchforum.org/new...-not-polymodal

    The use of genetically encoded calcium indicators in vivo reveals polymodality is a rare phenomenon in dorsal root ganglion (DRG) sensory neurons. Instead, most of these neurons respond specifically to a single type of sensation, such as mechanical stimulation, cold, or heat, reports a team of researchers led by Edward Emery and John Wood, University College London, UK.

    “This paper applies a new technique to an old question of whether DRG neurons respond to one or more sensory modalities,” says David Yarmolinsky, Boston Children’s Hospital, US, who was not involved in the new study. “Unlike electrophysiological experiments, which examine single neurons, this calcium imaging technique allows researchers to really see how the system as a whole responds, which affords a more meaningful sense of how pain is produced. The approach has distinct advantages over studying pain neurons in a dish.”
    Some of you may want to take a look at the comments on this one.
    Last edited by Jo Bowyer; 24-02-2017, 05:53 PM.
    Jo Bowyer
    Chartered Physiotherapist Registered Osteopath.
    "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

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