The ability to feel pain is essential for survival as it enables us to avoid situations that may cause injury and it alerts us to the fact that something is wrong with the body. Until now, it was believed that pain sensors are equally receptive to all kinds of pain, however, new research carried out by University College London suggests that pain-sensing neurons are specialised for specific types of painful sensations.
The neurons responsible for alerting us of potentially damaging external factors are called nociceptors. They are organised in a peripheral network that detects extreme temperatures, pressure, and injury-related chemicals. The new research gives insight in to how these pain sensors actually work.
Previous research on pain has traditionally used electrodes to examine pain-sensing neurons, but the efficacy of this testing model is limited. Many scientists feel that pain-assessment models based on electrodes are invasive and that they alter the neurons' properties.
In the latest study, led by Dr Edward Emery from UCL's Wolfson Institute for Biomedical Research, the researchers used a non -invasive, fluorescent activity-dependent imaging to study pain-sensing neurons in mice. The pain-receptive neurons were genetically marked to emit a fluorescent glow when activated.
The mice were either slightly pinched or exposed to cold and hot water stimuli on their paws to see which neurons were activated.
The results showed that over 85 percent of pain sensors react only to specific types of pain, while being unresponsive to others.
Dr Emery believes that previous research was compromised by the invasive electrode-based form of assessment, which mistakenly showed that pain sensors are responsive to all kinds of pain when they are actually quite selective in their response.
Improving effectiveness of painkillers
Commenting on the new research he said: "While the majority of neurons are specific to one type of pain, they can become universal pain sensors when the tissue is damaged. This may explain the discrepancies between our findings and those from other studies where more invasive approaches have been used."
Senior author of the study, Professor John Wood, said: "Our next step is to look at animal models for specific chronic pain conditions to see which neurons cells are activated. We hope to identify the different neurons through which chronic pain can develop, so that focused treatments can be developed.”
The results of the study are published in the journal Science Advances.
