Itch can't help scratching? Tachykinin neurons are the "culprit"

Why do people itch? Why can tickle again? This is not only painful for patients with chronic itching, but also a big problem that has long plagued scientists Recently, sun Yangang, a researcher at the Institute of neuroscience, Chinese Academy of Sciences, led the team to supplement the mechanism of itch regulation and solve the mystery of "itch scratch" vicious circle   The team found a group of neurons expressing tachykinin in the brain by using in vivo electrophysiological recording, in vivo optical fiber recording, pharmacological genetics and light genetic manipulation These neurons regulate the spinal cord horizontal itch information processing and promote the generation of scratching behavior through the down loop   The research revealed the cell and neural loop mechanism of down regulation of itch sensation, which provided a new way to develop the treatment of chronic itch   Few studies on the mechanism of itch information processing
Itching is an unpleasant feeling that can cause scratching Whether it's scratching or biting by mosquitoes, it's unbearable Like vision and hearing, itching is also a product of brain processing   Although uncomfortable, itching is essential for animal survival Sun Yangang told SciTech daily that itching can lead to scratching, which can help animals get rid of harmful substances on their skin So itching is also one of the important protective mechanisms of animals   However, itching is not easy Chronic itching patients often lead to skin and deep tissue damage due to uncontrollable excessive scratching Sun said that at present, our understanding of the mechanism of itch information processing is very little, so there is a lack of effective treatment for chronic itch   According to sun Yangang, in the field of itch research, previous researchers mainly explored the molecular and cellular mechanisms of itch in the skin, sensory neurons and spinal cord Especially in the past 10 years, a lot of researches have revealed the information transmission mechanism of itch sensation in the peripheral nervous system and spinal cord In contrast, there are few studies on how the brain processes and dynamically regulates itch sensation The regulatory role and mechanism of periaqueductal gray matter in itch sensation are not clear "We hope to provide a new target and theoretical basis for the treatment of chronic itch by studying the neural mechanism of itch information processing." Sun said   Successfully found the itch neuron
In mice, the team studied the cellular and neural mechanisms of periaqueductal gray in the regulation of pruritus The team found that activating neurons in the brain that express tachykinin induced strong scratching in mice, suggesting that the activation of these neurons tickled the animals   The team was surprised by this result "We found that there are a group of excitatory neurons expressing tachykinin in the brain In the scratching behavior caused by itching, these neurons are activated, and the activation of these neurons also causes the strong scratching behavior of mice So these tachykinin neurons seem to be the itch neurons in the brain Sun explained   How does the activation of tachykinin neurons lead to itching? "Our skin is constantly stimulated by external itching However, because these stimuli are weak and below a certain threshold, we usually do not feel itchy This threshold is set by some inhibitory neurons in the spinal cord Sun Yangang said he made an example: these inhibitory neurons block external itching stimulation like a "door" Only when external itching stimulation exceeds a certain threshold, can the door be pushed open to cause itching The tachykinin neurons in the brain found in this study help to open the door and reduce the threshold of itching   "This study is the first to identify a subset of neurons in the brain involved in the regulation of itch information." Sun said Further study confirmed that killing or inhibiting the tachykinin neurons in the periaqueductal gray could significantly reduce the scratching behavior induced by itch On the contrary, activating them can induce strong scratching behavior without external itching stimulation   In addition, adverse emotions such as stress or anxiety are likely to affect the sensitivity of itch sensation by regulating these tachykinin neurons in the brain "Therefore, these tachykinin neurons in the brain may be potential targets for curbing the tickling scratching vicious cycle and treating chronic itch." Sun said   It can not be directly used in clinical practice
"This study has changed the traditional thinking of solving chronic itching The results show that it may be a new way to treat chronic pruritus to intervene the neurons in the brain which are responsible for the information processing of pruritus Sun said   But he also admitted that the new research can not be used to improve the situation of patients with chronic itch The study uses mice as animal models, and it can not be ignored that there may be species differences between human and mice Although the study has determined that tachykinin neurons in the brain are essential for promoting the itch scratch cycle, the team used some invasive methods to manipulate these neurons "There is still a lack of noninvasive ways to manipulate these tachykinin neurons to treat chronic itching." "At present, our research can not be directly used in clinical practice," Sun said In order to apply these results, we must also identify molecular targets that can target tachykinin neurons in the brain "
Referring to the follow-up plan for this research in the future, Sun said that the neural network for sensory information processing and regulation is extremely complex "We plan to further determine the core neural circuit for itch information processing based on the current research, which will help to understand how itch information is processed and regulated in the brain In addition, we will identify molecules that are selectively expressed in tachykinin neurons Among these molecules, we hope to find drug targets for chronic pruritus.