The study illustrates the neural loop mechanism of pain information processing.

Recently, a research paper by sun Yangang, a researcher at the center for excellence and innovation in brain science and intelligent technology, Chinese Academy of Sciences (CAS), Shanghai brain science and brain like research center, and State Key Laboratory of neuroscience, was published online in "neurons" with the title of "parabrachial nucleus transmitting pain information of ascending spinal cord directly to thalamic lamellar nucleus instead of amygdala" 》Go ahead.this study elucidates the cellular and neural mechanisms underlying the long-term transmission of pain related information and the induction of protective behavior.pain is an important way for people and animals to perceive the changes and threats of internal and external environment, and plays an important role in maintaining individual survival and health.however, chronic pain brings pain to patients and affects their quality of life, which is one of the important clinical problems to be solved urgently.further analysis of the neural mechanism of pain information processing will help to find new targets for chronic pain treatment.in recent years, progress has been made in the molecular and cellular mechanisms of pain information processing at the spinal level.however, little is known about how pain related information is transmitted from the spinal cord to the brain, which limits the in-depth analysis of neural circuits related to pain information processing in the brain.previous studies have shown that spinal projection neurons transmit somatosensory information to multiple brain regions, including thalamus, periaqueductal gray matter, solitary tract nucleus and parabrachial nucleus.using the method of virus tracing, the researchers found that the projection neurons from the unilateral spinal cord projected to the ipsilateral and contralateral parabrachial nucleus at the same time, which was quite different from the contralateral projection pattern of the spinal cord projecting to other brain regions.animals often show protective licking behavior after local injury or inflammatory reaction.the researchers used pharmacological genetics and photogenetics to study the role of ipsilateral and contralateral spinal cord parabrachial nucleus loops in protective licking induced by inflammatory pain.it has been found that inhibition of ipsilateral spinal cord parabrachial nucleus loop can significantly reduce licking behavior induced by inflammatory pain, but inhibition of contralateral spinal cord parabrachial nucleus loop has no effect on licking behavior.consistent with the above results, the activation of ipsilateral spinal cord parabrachial nucleus loop can induce licking behavior, while activation of the contralateral circuit can not induce licking behavior.the study further found that most of the neurons in the parabrachial nucleus that received spinal cord input expressed tachykinin type I receptor (tacr1). In addition, tacr1 positive neurons can be selectively activated by a variety of noxious stimuli and play a key role in pain information processing.it has been speculated that the parabrachial nucleus may transmit the ascending somatosensory information from the spinal cord to the amygdala.contrary to previous conjectures, this study found that the cells in the parabrachial nucleus receiving spinal cord input form direct excitatory synaptic connections with neurons in the thalamic laminar nucleus rather than the amygdala.these results suggest that the ipsilateral spinal parabrachial nucleus loop transmits pain related information from the spinal cord directly to the thalamic laminar nucleus rather than the amygdala.this study revealed the cellular and loop mechanisms of pain related information transmission in the spinal cord, and laid a foundation for further study on the plasticity and regulation mechanism of pain information processing loop.under the guidance of sun Yangang, this study was mainly completed by Dr. Deng Juan. Zhou Hua, a member of the laboratory, made important contributions, and was supported by Xu Xiaohong, a researcher at the brain intelligence Excellence Center.the research work is supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China and Shanghai Municipality.note: ipsilateral parabrachial nucleus circuit directly transmits pain information from the ascending spinal cord to the thalamic laminar nucleus rather than the amygdala.the spinal cord projection neurons project to the contralateral (white line) and ipsilateral (yellow line) parabrachial nucleus.most of the neurons in the parabrachial nucleus receiving spinal cord input are distributed in the dorsolateral parabrachial nucleus (red). These neurons mainly project to the thalamic lamellar nucleus (pink line), with a small amount of connections (blue thin lines) with the amygdala.a small number of neurons in the parabrachial nucleus receiving spinal cord input were distributed in the ventrolateral parabrachial nucleus (blue).source: brain science and intelligent technology innovation center of Chinese Academy of Sciences