Neuron: How can dangerous gas leaks be quickly sensed and trigger escape behavior?

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The olfactory system can be used as a danger signal detector and early warning system, triggering a defensive response that is vital to survival
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Mice use vomeronasal sensory neurons (VSN) to detect chemical stimuli from individuals of the same kind.
Pathogen-related bacteria-derived molecules activate G-protein coupled chemoreceptors in these neurons to drive avoidance.
Predator induces The escape behavior is mainly related to neurons in the olfactory epithelium (MOE)
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Chemosensory in the mouse olfactory system mainly occurs in two chemosensory epithelium in the nasal cavity: olfactory epithelium (MOE) and vomeronasal epithelium
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The typical chemosensory neuron in MOE, the olfactory sensory neuron (OSN), expresses about 1,000 odorant receptor (OR) genes
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OSN relies on the cyclic nucleotide gated (CNG) cation channel activated by the second messenger cAMP, which is encoded by Cnga2
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Each olfactory sensory neuron (OSN) expresses only one olfactory receptor (OR) gene in a monoallelic manner, and its axons project to the olfactory bulb
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The typical chemosensory neuron in the vomeronasal epithelium, the vomeronasal sensory neuron (VSN), relies on the transient receptor potential (TRP) channel for chemosensory signal transduction, which is encoded by the Trpc2 gene
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Hydrogen sulfide is usually produced by bacteria decomposing organic matter under anaerobic conditions, so it usually occurs at the same time as oxygen consumption
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Rodents, as burrowing animals, need to be extremely sensitive to dangerous gas signals such as low oxygen or hydrogen sulfide to protect themselves and their offspring from death due to lack of oxygen
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On July 12, 2021, the joint research team of Frank Zufall, Saarland University, Germany, and Peter Mombaerts, Max Planck Institute, Germany, mice sense hydrogen sulfide dangerous gas signals through the B-type cells of the olfactory epithelium to trigger defensive behavior
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There is a type of neuron that co-expresses two transduction channels Cnga2 and Trpc2 in MOE, that is, type B cells
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Soluble guanylate cyclase Gucy1b2 is used as a marker for type B cells
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The distribution of chemoreceptors in B-type cells.
Researchers using Gucy1b2-GFP mice found that Cnga2 is mainly located in the cilia of B-type cells, while Trpc2 is mainly expressed in the dendritic nodes of B-type cells
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This anatomical difference indicates that different chemical stimuli may activate type B cells through different chemoreceptive pathways
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Exogenous hydrogen sulfide can activate type B cells at a lower concentration.
In addition, low oxygen can also activate type B cells, which indicates that type B cells can sensitively detect two different life-threatening gas stimuli in the external environment ( Hydrogen sulfide, hypoxia) changes
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B-type cells' perception of hydrogen sulfide after knocking out Cnga2 or Trpc2.
Researchers further found that after specifically knocking out Cnga2 on B-type cells, hypoxia can still activate B-type cells, but hydrogen sulfide cannot activate this type of cell; After the specific knockout of Trpc2, hydrogen sulfide can still activate type B cells, but it is not sensitive to hypoxia
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These results indicate that type B cells rely on Cnga2 to detect hydrogen sulfide gas signals and Trpc2 to detect hypoxia signals
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The olfactory system triggers various defensive and aversive behaviors in mice after detecting dangerous chemical stimuli
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Under normal circumstances, hydrogen sulfide can cause obvious conditional position preference behavior in mice (the mice are unwilling to stay on the side of hydrogen sulfide gas), cause the concentration of peripheral ACTH, and the repeated grooming behavior to increase; but when Cnga2 is knocked out Later, the mice lost the ability to perceive the danger of hydrogen sulfide, and remained on the side of hydrogen sulfide gas, and repeated grooming behaviors were reduced
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In summary, this article reveals that there is a type of B cell that simultaneously expresses Cnga2 and Trpc2 in the olfactory epithelium.
The former is located on the cilia and detects the hydrogen sulfide signal; the latter is located on the dendritic node and detects the hypoxia signal, which is beneficial The survival of rodents
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It is worth noting that in humans Gucy1b2 and Trpc2 genes are a kind of "pseudogenes", which means that these genes do not encode proteins [Reference] 1.
https://doi.
org/10.
1016/j.
neuron .
2021.
05.
032 The pictures in the text are all from the original reference.
Download link: https://pan.
baidu.
com/s/1jimcblDl37YuhJZzai6gdQ Extraction code: 8w2u