Summary: Researchers discover over 85 percent of pain sensing neurons are sensitive to one specific type of pain event.
Many pain-sensing nerves in the body are thought to respond to all types of ‘painful events’, but new research reveals that in fact most are specialized to respond to specific types such as heat, cold or mechanical pain.
The study, published in Science Advances and funded by Wellcome and Arthritis Research UK, found that over 85% of pain-sensing neurons in whole organisms are sensitive to one specific type of painful stimulus. It was previously thought that most pain-sensing neurons were very similar, so the new finding could enable scientists to develop new specific painkillers for different pain conditions.
Previous research using electrodes to monitor pain-sensing neurons had suggested that they respond to all types of pain, but the new study suggests that this recording technique may have altered the neuron’s properties.
“While the majority of neurons are specific to one type of pain, they can become universal pain sensors when the tissue is damaged,” explains lead author Dr Edward Emery (UCL Wolfson Institute for Biomedical Research). “This may explain the discrepancies between our findings and those from other studies where more invasive approaches have been used.”
The team used a form of fluorescent activity-dependent imaging, where pain-sensing neurons in mice were genetically marked to emit a fluorescent glow when activated. The mice were briefly exposed to either a small pinch, cold water or hot water stimulus on one of their paws to see which neurons were activated. The results showed that over 85% of pain-sensing neurons were specific to one type of pain and did not react to others.
“Our next step is to look at animal models for specific chronic pain conditions to see which neurons cells are activated,” says senior author Professor John Wood (UCL Wolfson Institute for Biomedical Research). “We hope to identify the different neurons through which chronic pain can develop, so that focussed treatments can be developed. We use ‘chronic pain’ to describe all sorts of pain conditions with different causes, but we now need to differentiate them so that we can develop new specific treatments.”
Source: Harry Dayantis – UCL
Image Source: This NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP” by Edward C. Emery, Ana P. Luiz, Shafaq Sikandar, Rán Magnúsdóttir, Xinzhong Dong and John N. Wood in Science Advances. Published online November 11 2016 doi:10.1126/sciadv.1600990
[cbtabs][cbtab title=”MLA”]UCL. “New Theory Debunks Idea That Math Abilities Are Inate.” NeuroscienceNews. NeuroscienceNews, 11 November 2016.
<https://neurosciencenews.com/pain-sensor-sensation-5495/>.[/cbtab][cbtab title=”APA”]UCL. (2016, November 11). New Theory Debunks Idea That Math Abilities Are Inate. NeuroscienceNews. Retrieved November 11, 2016 from https://neurosciencenews.com/pain-sensor-sensation-5495/[/cbtab][cbtab title=”Chicago”]UCL. “New Theory Debunks Idea That Math Abilities Are Inate.” https://neurosciencenews.com/pain-sensor-sensation-5495/ (accessed November 11, 2016).[/cbtab][/cbtabs]
In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP
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.
“In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP” by Edward C. Emery, Ana P. Luiz, Shafaq Sikandar, Rán Magnúsdóttir, Xinzhong Dong and John N. Wood in Science Advances. Published online November 11 2016 doi:10.1126/sciadv.1600990