PNAS︱Qin Hongtao/Chen Peng's research group collaborated to reveal that dopaminergic neurons regulate chronic stress-induced memory impairment in Drosophila

Written by Zhang Mengyu, edited by Wang Sizhen Drosophila melanogaster (Drosophila melanogaster) is named after the black digestive tract can be seen on the abdomen side of its larva.
It is one of the most successful genetic model organisms
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Although the anatomical structures of the brains of Drosophila and mammals are very different, many basic elements and functions of the nervous system are well conserved
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Like higher animals, fruit flies can also form associative memories
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The learning and memory nerve centers of adult flies are two symmetrical mushroom bodies (MB)
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The learning loop of the mushroom body mainly involves three types of neurons, Kenyon Cells (KC), dopamine neurons (DANs), and MB Output Neurons (MBONs)
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The axons of about 2000 KCs bind together to form the stalk and lobe of MB, while the neurites of DANs and MBONs project to different areas of the MB lobe
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 Stress (commonly known as stress) has a significant impact on cognitive function, and long-term or excessive stress exposure often damages learning and memory [1]
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Since stress is an important cause of major depression, chronic stress animal models are used to simulate depression
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Although animal models of depression are mainly modeled by mammals, especially rodents, chronic stress can also induce depression-like symptoms in Drosophila, showing characteristic behaviors such as anhedonia, lack of motivation, easy despair, and sleep disorders [ 2-4]
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Environmental stress can also affect the learning and memory of fruit flies
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However, the research on the effect of chronic stress on learning and memory of Drosophila and its mechanism is still lacking
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 On October 16, 2021, the Hongtao Qin group of Hunan University and the Chen Peng group of Kunming Medical University jointly published a paper titled "A pair of dopamine neurons mediate chronic stress signal to induce learning deficit in Drosophila melanogaster" on PNAS online.
Research articles
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Jia Jia, Yang Junfei and He Lei, postgraduates majoring in biomedical engineering at Hunan University, are the first authors of equal contributions
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This paper reported for the first time that chronic stress-induced learning deficit (CSLD) is related to the depression-like state of Drosophila melanogaster, and initially revealed the neural circuit mechanism of the dopamine nervous system that regulates susceptibility to CSLD
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 First, the authors established a paradigm of chronic stress-induced learning disabilities (CSLD) (Figure 1A), and phenotype identification of fruit flies that had been treated with chronic stress for 4 days
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The results showed that Drosophila exhibited a series of depression-like behaviors, including cognitive impairment (deficiencies in olfactory learning and mid-term memory), delayed courtship [5], anhedonia (decreased number of stops to eat during climbing [3], Prone to despair (giving up struggling early in the forced swimming test) [6] (Figure 1B-H)
.
What is
interesting is that chronic stress-induced forced swimming deficits and learning deficits can last for at least two days (Figure 1G-I)
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These results indicate that the chronic stress paradigm may induce depression-like states in Drosophila, thus exhibiting a variety of depression-like behaviors including CSLD
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Figure 1 Long-term stress can lead to olfactory learning and memory deficits and other depression-like behaviors in Drosophila (Source: Jia Jia et al.
, PNAS, 2021).
Then the paper focused on the CSLD phenotype, exploring the dopaminergic nervous system and CSLD The relationship of susceptibility
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The author has carried out two-way regulation of dopamine synthesis through drug feeding (3-IY inhibits dopamine synthesis, and L-DOPA promotes dopamine synthesis)
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It was found that too high levels of dopamine would promote the susceptibility of CSLD (Figure 2 B, C); and the use of genetic manipulation to regulate the expression of dopamine D1 receptor Dop1R1 in both directions (deletion mutant heterozygous Dop1R1dumb2/+ knockdown Dop1R1[7,8], Gal4/UAS drives the overexpression of Dop1R1 in MB) shows that excessive dopamine receptor signaling can cause chronic stress-related learning and memory impairment (Figure 2D-E); further use of temperature genetics to DANs The activity is manipulated in two directions (TH-Gal4/UAS-ShiTS1 can be used to inhibit the release of DAN neurotransmitters, and TH-Gal4/UAS-TrpA1 can artificially activate DAN [9,10])
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The results indicate that the overactive DAN activity during shock stress treatment also promotes the susceptibility to CSLD (Figure 2F-H)
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Summary: Experimental evidence at the three levels of dopamine, dopamine receptors and dopamine neurons consistently shows that excessive dopaminergic activity induced by chronic stress treatment can increase the susceptibility of Drosophila to CSLD
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Figure 2 The susceptibility to CSLD is regulated by the dopaminergic system (Source: Jia Jia et al.
, PNAS, 2021) There are about 200 DANs in the brains of adult flies [11]
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In order to find the important DAN that regulates CSLD, the author used the temperature genetics tool mentioned above to screen the DAN projected to MB
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It was found that simply blocking PPL1-γ1pedc neurons is sufficient to effectively prevent CSLD (Figure 3D-G), while blocking other neurons has no significant effect on CSLD (Figure 3B, C)
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Conversely, chronic artificial activation of PPL1-γ1pedc can replace chronic shock stress treatment and induce significant learning disabilities
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It can be seen that PPL1-γ1pedc is the key DAN that mediates chronic stress signals to induce CSLD, and overactive PPL1-γ1pedc can promote the occurrence and development of CSLD
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It is worth noting that the PPL1-γ1pedc neurons in the brains of adult flies only have a pair of left and right symmetrical neurons
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Figure 3 The activity of PPL1-γ 1pedc DANs can promote susceptibility to CSLD
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(Image source: Jia Jia et al.
, PNAS, 2021) MB is the brain area whose anatomical structure has been studied most clearly
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PPL1-γ1pedc and MBON-γ1pedc>α/β projected to the same area on the MB leaf
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The activity of PPL1-γ1pedc can weaken the synaptic connection strength between KC-MBON-γ1pedc>α/β[10,12]
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Therefore, the author guessed that the effect of activating MBON-γ1pedc>α/β on CSLD should be similar to that of blocking PPL1-γ1pedc activity
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Indeed, experiments have shown that activating MBON-γ1pedc>α/β during the shock treatment can prevent the occurrence of CSLD (Figure 4A, B); and chronic blocking the activity of MBON-γ1pedc>α/β is also sufficient to induce learning disabilities.
(Figure 4C)
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Figure 4 MBON-γ1pedc>α/β neurons regulate CSLD susceptibility
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(Source: Jia Jia et al.
, PNAS, 2021) After that, the author used two neuroactivity reporting systems, CaLexA[13] and ANF-GFP, to detect whether the activity of MB-related neurons after chronic stress treatment Behaving abnormally
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The experimental results found that the CaLexA signal of α'/β' KCs was weakened, indicating that the accumulated neural activity was reduced (Figure 5A, F), while the ANF-GFP signal of MBON-γ1pedc>α/β was down-regulated, indicating that its neural activity was enhanced (Figure 5A, F).
5 D, I)
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In addition, the increased CaLexA signal of γ-KCs in male flies indicates that their neural activity has also increased
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Importantly, the normal functions of these three types of neurons are all necessary for olfactory learning in Drosophila
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The additive effects of these neurological abnormalities may be the neurophysiological basis of CSLD
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Finally, the use of 3-IY feeding (down-regulation of DA levels) can effectively alleviate the abnormal α'/β' KCs activity induced by chronic stress (Figure 5E, J), indicating that dopaminergic activity is also chronic stress-induced learning-related neural activity Necessary conditions for exceptions
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Figure 5 Chronic stress induces abnormal neural activity of MB network (Source: Jia Jia et al.
, PNAS, 2021) Conclusion and discussion of the article, inspiration and outlook So far, the overall experimental evidence supports such a model: the signal process of chronic stress A pair of PPL1-γ1pedc DANs mediate the afferent mushroom body and drive the maladaptive neural network of the mushroom body to induce CSLD
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This study created a Drosophila model for studying chronic stress-induced learning and memory impairment, and further confirmed that the Drosophila chronic stress paradigm is an effective depression-like animal model
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Research on the etiology of CSLD shows that the dopaminergic system has an evolutionarily conservative and important regulatory effect on the susceptibility to CSLD
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Given that the Drosophila model has a wealth of molecular genetic tools, and its brain connection group has been completed, in-depth studies on CSLD are expected to finally clarify the molecular neural mechanism of chronic stress damaging the neural circuits of learning and memory, which is a major cause of stress-related cognitive impairment Treatment provides important clues and basis
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 While this research has spawned a new research direction, there are also many unsolved problems, such as: 1.
The main effect stimulus used in the article is mechanical shock, a physical stressor
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In modern society, more stressors related to depression are social or psychological
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Is it possible to use psychological stressors to build a depression-like model of Drosophila so as to better simulate depression? 2.
The article found dopamine neurons that mediate stress signals, but where the upstream signals of dopamine neurons come from, the article did not discuss it; 3.
The article mainly focuses on the analysis of neural circuits related to CSLD susceptibility , Did not pay attention to the molecular mechanisms regulating CSLD susceptibility
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If the advantages of Drosophila genetic model organisms can be used to discover conservative genes that regulate CSLD susceptibility, the value of Drosophila depression-like models will be more convincing
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Original link: https:// Co-first authors of this article: Jia Jia (left one), Yang Junfei (middle), He Lei (right one) (photo provided by: Tan Hongtao laboratory) in this paper together by a plurality of units, participants will include the Hunan University, Kunming Medical University, Howard Hughes Medical Institute Janelia Farm Research Park, the CAS Institute of Biophysics, Chinese Academy of Sciences University
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Hunan University is the first communication unit
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 The research was funded by the National Natural Science Foundation of China, the Natural Science Foundation of Hunan Province, and the Natural Science Foundation of Yunnan Province.
It also received support and help from many domestic and foreign counterparts
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 Professor Qin Hongtao's research group has been studying the mechanism of brain regulation of behavior and physiology for a long time, and his current research interests are concentrated in the field of stress neurobiology
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Use molecular biochemistry, biological information, behavior, immunohistochemistry, imaging and other related experimental techniques to systematically study the neural and molecular mechanisms of the pathogenesis and development of stress-related neurological diseases
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The research group is recruiting post-doctoral fellows and research assistants.
If you are interested, please email qinhongtao@hnu.
edu.
cn
.

Selected articles from previous issues [1] Nat Commun | Working memory representation of the visual cortex regulates the distraction effect [2] Science | Breakthrough! Immune CD4+ T cells are involved in the disease process of Lewy body dementia [3] Cell Rep︱ new research reveals the role of hypothalamic neuronal calcium homeostasis regulators in the formation of obesity [4] Science︱ first confirmed in humans: multiple neurodegeneration Sexual diseases can affect the neurogenesis of the hippocampal dentate gyrus [5] Neuron︱ new discovery! The hippocampus playback in the awake state promotes memory function by storing and updating specific past experiences [6] Mol Psychiatry︱ A new discovery of biomarkers for depression-mitochondrial proteins in exosomes [7] Science | Breakthrough! Astrocyte Ca2+ induces ATP release to regulate myelin axon excitability and conduction velocity [8] Neurosci Bull︱Shen Ying’s team reveals the three-dimensional heterogeneity of the cerebellar nucleus to thalamus projection [9] J Neurosci︱ Cao Junli’s group Revealing the loop mechanism of the anterior cingulate gyrus to regulate mirror pain [10] Nat Commun︱Non-human primate (monkey marmoset) autism model Revealing biological abnormalities in the early development of human diseases High-quality scientific research training courses recommended [1] Discount Countdown ︱ EEG data analysis introductory class (online: 2021.
12.
4~12.
16) [2] Discount countdown︱ Near-infrared brain function data processing class (online: 11.
1~11.
14) [3] Data graph help guide! How good is it to learn these software? 【4】JAMA Neurol︱Attention! Young people are more likely to suffer from "Alzheimer's disease"? References (slide up and down to view) 1McEwen, BS et al.
Mechanisms of stress in the brain.
Nat Neurosci 18, 1353-1363, doi:10.
1038/nn.
4086 (2015).
2Araujo, SM et al.
Chronic unpredictable mild stress- induced depressive-like behavior and dysregulation of brain levels of biogenic amines in Drosophila melanogaster.