24 Feb Leaky Gate Model Connects Intense Itch With Pain

MedicalResearch.com Interview with:

Dr. Xinzhong Dong

Xinzhong Dong PhD
The Solomon H. Snyder Department of Neuroscience and Center for Sensory Biology
Howard Hughes Medical Institute
Johns Hopkins University School of Medicine
Baltimore, MD 21205

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: It is a puzzle that troubles the field for many years that how pain and itch, two closely related sensations (once thought as one sensation), are differentiated by the nervous systems. Coding of pain and itch are heatedly debated for decades. The current specificity theory suggests that these two kinds of signals are carried by separate pathways, with some interactions, for example pain can inhibit itch and that explains why we all scratch to inhibit pain. It is true in the periphery (our previous study indicate a small population of neurons in the periphery only codes for itch sensation), but now our study suggests that there could be more crosstalk between these two sensations in the central than we expected.

People might not notice in real life, but in human psychophysical studies, well-isolated experimental environments, when human subjects are given itchy substances, they typically report intense itch sensations accompanied by minor noxious sensations, such as pricking, stinging and burning. Our new leaky gate model suggest in certain circumstances intense itch signals can trigger minor pain sensations, which can explain such phenomenon.

MedicalResearch.com: What should readers take away from your report?

Response: We found an interesting neuronal mechanism that allow us to preserve pain sensitivity to weak harmful stimuli but at the meantime not overwhelmed by strong painful stimuli.

Our new leaky gate model also suggests that in certain circumstances intense itch signals can trigger minor pain sensations, which can explain observations from human psychophysical studies that itchy chemicals trigger weaker noxious sensations accompanying itch in human subjects.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: We would like to further explore the circuits downstream, as we mentioned these neurons are only the first step in central nervous systems. We would like to know how pain and itch signals are further relayed from spinal cord to higher brain areas and see whether maladaptive changes in these circuitries might contribute to chronic pain and chronic itch conditions.

MedicalResearch.com: Is there anything else you would like to add?

Response: We think this leaky gate model builds on the previous models and expands our knowledge as how pain and itch can be coded in the central nervous systems. It might sound somewhat counter-intuitive at the beginning that when you have a stronger input, the responses are actually weaker, but we think it makes sense, because this small population of cells actually functions as a brake for pain and this brake only works during strong painful stimuli so that we can still detect weak painful signals with enough sensitivity and it also makes sure that our sensitive pain detecting system is not generating too much pain when strong painful signals come in.

The leaky gate model is somewhat more complicated than the previous coding models, but we think it reflects the complex coding that actually happens in the central nervous system, which we don’t know enough yet.

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.

Citation:

Volume 93, Issue 4, p840–853.e5, 22 February 2017
Leaky Gate Model: Intensity-Dependent Coding of Pain and Itch in the Spinal Cord
Shuohao Sun, Qian Xu, Changxiong Guo, Yun Guan, Qin Liu, Xinzhong Dong
DOI: http://dx.doi.org/10.1016/j.neuron.2017.01.012

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Last Updated on February 24, 2017 by Marie Benz MD FAAD