Why is it important to have fear?

In daily life, we often feel fear, fear of something dangerous (such as snakes, or other toxic animals), fear of heights, afraid of bad people, and so on.' 'fear"' is a kind of all the animals have emotions.When animals perceive is likely to be hurt, will fear, and enter a temporary state of alert.The animal's response to fear, to help them in dangerous situations to protect our.fear感是由大脑中的一些区域产生的，例如杏仁体，扣带皮层，以及中脑中一个叫做导水管周围灰质的区域。它们与感官（视觉、听觉、嗅觉、触觉和味觉）协同起来产生对于危险的反应 [1].Our senses to make us afraid, to remind us of the potential danger.We are surprised by a loud noise, for example, to experience, or to cast a shadow suddenly, in an instant thought what animals.Despite fine is impossible to think of it, will be scared.For animals, fear is very important in our daily life.It is a kind of instinct to protect, to help identify potential and real dangerous animals.

In addition, the fear is important, but also because when it is excessive, could lead to ' 'anxiety"' barriers.Although many researchers think that fear and anxiety are two different things, but both contain for dangerous negative feelings.When we think bad things will happen, we feel anxious;And when we truly after bad things, we will feel fear.anxiety障碍是当今世界上主要的健康问题之一，而目前无法很好地治疗。但现在关于恐惧的新发现，也许能帮助我们更好地医治焦虑障碍。

Use animals to study the fear

Through the study of human, we have a little bit knowledge of fear - for example, through the use of neuroimaging (this kind of technology can help scientists to see what is happening in the brain) to explore people feel afraid, what happened to their brain (As shown in figure 1) - but this is not an easy task.First of all, the current neuroimaging technology can only measure brain activity within certain depth, so the more deep in the area (including the midbrain is important for fear of the area), it is difficult to use the existing technology.Second, in the lab, it is difficult to make people afraid to ensure safety at the same time, because most can make us feel very afraid of things that are more or less real harm to us, so we are difficult to study people's reactions to fear in the laboratory.In the end, find people who volunteered to participate in such experiments is also very difficult.Therefore, so far, we fear to understanding, and knowledge of how the brain to control the emotions, mostly come from animal research.

In scientific research, the animals can help us understand the human body the same behavior.Although we tend to think of at the mention of laboratory rats and mice, but in fact, many species will be used to this kind of experiment, including flies, rabbits, dogs and fish.Some researchers think that only the rodents (rats and mice) will limit our exploration of the human brain [2].So neuroscientists (scientists who study the brain structure and function) found other reaction similar to the human animal.Zebrafish, a genetics, embryology and widespread use of animals in behavioral research, now gradually entered in neuroscience research.Zebrafish on genetic (DNA) and the body is similar to human (for example, similar brain), which makes them become the study of human good research object when anxiety disorder (As shown in figure 2).

Zebrafish alarm substance

Fear was studied by zebrafish has many advantages, one is that they, like many of these fish, were injured in the skin can produce a special kind of alarm material.This substance is produced by cells' ' ' 'club, the purpose is to inform other members of the fish have a fish was injured.For example, when the prey of a fish skin injury occurs, alarm material will be released, other fish can smell this kind of material.The smell of the 'dangerous'' let other fish become careful, was as if was afraid, and together to enhance protection.They can swim more irregular (zigzag lines), to reduce the likelihood of being eaten, and scooped up sediment (leaves, sand or mud in the bottom of the sea) make water turbidity.Zebrafish sometimes frozen where he was, and reduce the possibility of prey found [3].Neuroscientists and behavioral scientists can detect these behavior, to judge whether the fish was frightened, and then explore how brain when fear response.

One of the studies focus on something called ' 'serotonin' 'of the material.serotonin也称作 ''5-HT'' ，这是它的化学名字 ''5-羟色胺'' （5-hydroxytryptamine） 的英文缩写。它是一种被称作神经递质的化学物质。神经递质是神经元（神经细胞）和其它脑细胞在兴奋时释放的一种特殊化学物质。它使神经细胞之间，以及神经细胞和肌肉细胞、向血液中释放激素的细胞之间，能够进行交流。血清素最为人熟知的名字或许是 ''快乐激素'' ，常被用于治疗抑郁和焦虑。但事实却相差甚远：有证据表明，虽然血清素似乎会减轻恐惧感（我们不那么害怕真实发生的糟糕的事情了），但却会增加焦虑感（当我们感觉糟糕的事情即将发生时，会更加难受）。

Researchers now believe that when zebra fish smell alarm material to produce serotonin is involved in fear of process.2014 年，研究者发现当斑马鱼不再能嗅到警报物质时，警报物质会促使斑马鱼脑中血清素的释放 [4], which makes the fish more carefully, as if they are around to determine whether there are predators.But the serotonin is how to produce this effect?

Serotonin in the brain to work, must and one called ' 'receptor"Molecules.receptor是细胞中一种特殊的蛋白质，当与特定神经递质结合时，会产生特定反应，就好像一把钥匙插进了一把锁中。血清素有多种不同的受体，能产生多种不同的效应。当斑马鱼最开始闻到警报物质时，它们会表现得似乎很害怕，疯狂地游动，有时甚至会僵在原地；而在这种物质消散之后，它们不再害怕，但是会表现得 ''格外谨慎'' （焦虑），以确定危险的确已经不在周围。一些研究者发现 5-HT1A，血清素的受体之一，似乎与这种 ''格外谨慎'' 的状态并无联系 [4].But another study found that [5], if you give a zebrafish injection can block 5 - HT1A receptor drugs -- that is, make serotonin unable to play a role, so they smell alarm material will be more afraid of, but after disappeared in alarm substance will not.The researchers also found that other blocks serotonin receptors also there will be a similar effect, which suggests that serotonin can alleviate fears, but also make objects become more cautious after the alarm substance vanished,As shown in figure 3).

conclusion

Our brain (and zebrafish brain) deal with terrible situation every day.Your brain and your body ready to cope with something terrible to protect you, but will not let you cry in the case of threat is not sure ' ' ' 'a Wolf was coming.With the help of serotonin, we can then switch strategy in terrible situation: rapid escape from known risk, or careful exploration, and worries about dangerous if really exists.Through more of other neurotransmitters serotonin and zebrafish brain research, perhaps we can develop new drugs used to treat fear associated diseases.These findings will help us find a way to cure the anxiety disorder.

The vocabulary

Fear (Fear):writeAfter a big threat, people and other animals feel the psychological and physiological state.

Anxiety (Anxiety):writeWhen think have something bad will happen, the feeling extremely nervous.

Serotonin (Serotonin):writeBrain cells release a neurotransmitter role in other brain cells.

Receptor (Receptor):writeA protein found in our cells, with a particular matter (such as a hormone or neurotransmitter), and allows cells to respond.

Conflict of interest statement

The author statement, the study is in no may be interpreted as potential conflicts of interest under the condition of commercial or financial relationships.

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The original

writeMaximino, C., Costa, Lima, m. g. c. c. and Guedes, i. m. l., and Herculano, a. m. 2014. 100635 dissociate Fluoxetine and WAY - in scototaxis and analgesia induced by conspecific alarm substance in zebrafish,Danio rerioHamilton, 1822).Pharmacol. Biochem. Behav. 124:425-33. Doi: 10.1016 / j. bb 2014.07.003

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reference

[1]writeBezdek, k. g., and Telzer, e. h. 2017. Have no fear, the brain is here!How your brain responds to stress.Front. Young MindsFor 1. Doi:10.3389 / frym. 2017.00071

[2]writeGerlai, r. 2014. Fish behaviors in research: unique tools with a great promise!J. Neurosci. The Methods54-234:8. Doi: 10.1016 / j.j neumeth. 2014.04.015

[3]writeMaximino, Silva, r. C., x. do c., Campos, k. s. DOS, Oliveira, j. s. DE Rocha, s. p., Pyterson, m. P., et al. 2018. The chipmaker ecology of Ostariophysan alarm substances.Fish j. BiolDoi: 10.1111 / JFB. 13844

[4]writeMaximino, C., Costa, Lima, m. g. c. c. and Guedes, i. m. l., and Herculano, a. m. 2014. 100635 dissociate Fluoxetine and WAY - in scototaxis and analgesia induced by conspecific alarm substance in zebrafish,Danio rerioHamilton, 1822).Pharmacol. Biochem. Behav. 124:425-33. Doi: 10.1016 / j. bb 2014.07.003

[5]writeNathan, f. m., Ogawa, s., and Parhar, i. s. 2015. Kisspeptin1 modulates odorant - evoked fear response via two serotonin receptor subtypes (5 - HT_{1 a}And 5 - HT₂) in zebrafish.J. Neurochem. 133:870-8. Doi: 10.1111 / JNC. 13105