Nature reveals the latest neural loops that control feeding, or help with weight loss.

Learn about the latest progress in neuroscience ● click the blue word to pay attention to us ● classic experiments show that gastric distension can inhibit eating and drinking water, and the signal transduction involves vagus nerve and spinal cord afferent nerve.the digestive tract is widely innervated by cranial base nerves and spinal cord afferent nerves, which transmit sensory information to the posterior solitary tract nucleus (NTS).the nucleus tractus solitarius is a Y-shaped columnar nucleus located in the dorsal medulla oblongata and surrounding the solitary tract. It is the primary regulatory center of cardiovascular reflex, respiration, swallowing, vomiting and gastrointestinal reflex.studies have shown that NTS projects to the parabrachial nucleus (PB), which widely dominates many forebrain and midbrain regions related to eating and drinking water.this structure enables the parabrachial nucleus to play a key role in the control of mechanical sensation and feeding feedback.on April 8, 2020, sun Yong Kim, a young neuroscientist at Seoul University, Korea, published an article in the journal Nature, revealing new neural circuits that control feeding behavior, which may provide new research directions for the treatment of metabolic diseases.SUN Yong Kim mainly studies the relationship between stress and eating behavior, and his research results are of great significance for the treatment of obesity.using c-fos immunofluorescence, the researchers found that neurons expressing dynorphin in the parabrachial nucleus (hereinafter referred to as Pb PDYN neurons) were activated rapidly when drinking water.it was found that the calcium level of Pb PDYN neurons increased during drinking water and returned to the basic level after stopping drinking water.then whether the correlation between Pb PDYN neurons and drinking water is universal.further experiments found that the calcium level of Pb PDYN neurons increased no matter whether they drank liquid food, alkaline bicarbonate solution, normal saline or solid food such as feed, which indicated that the correlation of drinking water of Pb PDYN neurons was extensive, including almost all feeding behaviors.more interestingly, the change level of calcium ion in Pb PDYN neurons was highly positively correlated with diet speed, that is to say, the faster the mice ate, the more calcium ion level of Pb PDYN neurons increased.these results suggest that Pb PDYN neurons are involved in feeding.whether Pb PDYN neurons participate in feeding behavior and whether they receive mechanical sensory signals from digestive tract.researchers skillfully touch the tongue with the gavage needle (causing swallowing reaction) or inserting the gavage needle into the esophagus (causing gastrointestinal reaction) can cause strong response of Pb PDYN neurons, which indicates that the sensory signals of digestive tract can be transmitted to Pb PDYN neurons.the researchers further used physical methods to inflate the stomach, similar to flatulence. The results showed that Pb PDYN neurons had a strong response during gastric inflation, and the activity of Pb PDYN neurons decreased after deflation.surprisingly, the response of Pb PDYN neurons to dietary intake was not affected by the weight, temperature and smell of food, which indicated that the behavioral response of Pb PDYN neurons to food intake was stable. these results suggest that the main role of Pb PDYN neurons is to integrate the mechanical sensory signals from the digestive tract and further participate in feeding. by embedding grins lens above the parabrachial nucleus and combining with two-photon microscope technology, the researchers observed the changes of single Pb PDYN neurons when drinking water and eating solid food. They found that drinking water could activate about 82% of Pb PDYN neurons, and solid diet could activate about 75% PB PDYN neurons Big overlap. in addition, the activity of Pb PDYN neurons also increased after increasing the volume of intragastric gas (similar to flatulence). How do Pb PDYN neurons receive mechanical sensory signals from the digestive tract? One of them may be that there are neurons directly projecting to Pb PDYN neurons in the gastrointestinal tract, and the other is that there is a "transit station" in the process of gastrointestinal related signals transferring to Pb PDYN neurons. This paper reveals the second possibility based on the results of virus tracing technology. the researchers injected retrogressive trans monosynaptic rabies virus into the parabrachial nucleus, and found that almost all the brain fibers entered the parabrachial nucleus, which set up many difficulties in finding the "transfer station". However, the rostral and caudal inputs of the trigeminal nerve nucleus and the posterior solitary tract nucleus were the most. however, the function of the posterior solitary tract nucleus is highly related to gastrointestinal reactions. It receives oral, oropharyngeal and visceral sensory information transmitted through trigeminal, facial, glossopharyngeal and vagus nerves. therefore, they believe that the posterior nucleus of the solitary tract acts as a "transit station", which makes the input neurons in the cranial base ganglion and Pb PDYN neurons connect anatomically. this anatomical connection provides great convenience for vagus nerve to transmit gastric distention signal to Pb PDYN neurons. what role does Pb PDYN neurons play in feeding behavior? Chronic activation of Pb PDYN neurons or rapid activation of Pb PDYN neurons by chemical genetics technology can inhibit food and water intake. chronic inhibition of Pb PDYN neurons can promote excessive food and water intake, which indicates that Pb PDYN neurons negatively regulate feeding behavior. in conclusion, we have found a new neural loop to control feeding behavior. The digestive tract transmits sensory information to the nucleus retrotractus solitarius, and then further transmits the information to Pb PDYN neurons, thus negatively regulating feeding behavior. References: a neural circuit mechanism for mechanosensory feedback control of investment