A few weeks back I did a blog post on why some people itch, and some of the causes because of it. I wanted to find out a little bit more information about it so I did a little bit more digging.
Just to give some basic information about itching again, itching occurs when the skin is irritated by different things such as dust particles, dry skin, or skin diseases. I did find other information from an article from NBC News , that also talks about how itching is caused by how our brains process itching, and what tells our brains that we are itchy, but I am going to get into that a little more with some experiments that I found.
The experiments and observations that I found were all conducted by Dr. Zhou- Feng Chen who is the director of the Center for the Study of Itch at Washington University School of Medicine in St. Louis(Wustl.edu). The first observation that I found was Dr. Chen trying to see if the “GRPR(Gastrine- releasing Peptide receptor) which is a pain sensing gene is also an itch receptor. Dr. Chen found this when looking at the different genes in the spinal cord. Dr. Chen found that when mice with and without the GRPR gene were exposed to something that made them itchy, the mice with the gene itched more than the mice that did not have the gene. “(wustl.edu). Since this was an observation, direct causation is always a possibility, where that the GRPR gene is what causes the mice to itch more, but is it the same way with reverse causation? Can more itchiness cause the GRPR gene? I personally do not think so, I do not think itching can cause a gene. When it comes to chance it is also possible as well, because what if it just happened to be that some mice can get itchier that others? What if there was something else that was making them itch at the moment?
‘It is said when people itch, it also brings a sense of pain to the skin as well. When the skin starts to feel pain, pain signals are going up to our brains and not the itching signals.’ (wustl.edu.) When the body feels pain, serotonin which is a neurotransmitter, is sent out and tries to ease the pain. According to Dr. Chen ” But as the serotonin Spreads from the brain into the spinal cord, we found that the chemical can “jump tracks” moving from pain-sensing, neurons to nerve cells that influence itch intensity”(wustl.edu). He is basically saying that the serotonin plays a part in increasing the level of itchiness that people have. To prove this, Dr. Chen did another study with mice. “So what he did was that he bred mice that were not able to produce serotonin, and he then injected the mice with a substance that should make them itch, and compared them to mice with the serotonin, and saw that the mice without the serotonin did not itch whereas the other mice with it did. After that he then injected the mice without the serotonin with it and did the process over again and found that the mice started to itch.” (wustl.edu). Dr. Chen found that when itching”,this gives off pain signals to our bodies which then makes people itch even more”. (wustl.edu.) This was a controlled experiment which I think was conducted fairly well. Reverse causation could not play a factor in this because the itchiness could not cause the serotonin in the body. No third variable could be concluded because if conducted correctly Dr. Chen only had one variable being changed which was the Serotonin being put into the body of the mice. Chance can also be ruled out because the experiment was controlled.
The next experiment that Dr. Chen conducted went with the one above , but taken further. Knowing that the serotonin plays a part in itchiness Dr. Chen wanted to see if he could “interfere with the communication between the serotonin and the nerve cells in the spinal cord that dealt with itching directly.”(wustl.edu). To do this he wanted to see if he could “isolate the receptors that are used by the serotonin so he could activate the GRPR gene that I talked about earlier which is the neuron that mainly transmits itch.”(Wustl.edu). Dr. Chen is basically trying to see how all of these things work together. “To figure this out Dr. Chen injected mice with a substance that makes them itch,then gave mice compounds that activated various serotonin receptors on nerve cells( the serotonin is what was making the mice itch worse). He then found that a receptor called 5H1A which was the one activating the GRPR neurons.(the one that made the mice itch.) After he found that, he then proved this by blocking that receptor and found that the mice then began to itch less.” (wustl.edu). In the end Dr. Chen found that” serotonin activates the GRPR nueron through the 5H1A receptors”.(Wustl.edu). I thought this was a very well conducted experiment because after finding the certain receptor that was activating the GRPR neuron Dr. Chen checked this” by blocking out the receptor to see if the mice were still itching as much and they were not”.(wustl.edu) This I believe helped him get a more direct answer to his question because he proved his answer in another way instead of just concluding that the serotonin activated the neuron.
So basically with all of these observations and experiments, when it comes to itching a lot of it has to deal with ours brains and the different signals that our bodies tell us. I think Dr. Chen did a good job at trying to find this out when it came to his observations and experiments. With each of them, it led to finding something new to help with his questions about itching and how it comes upon us. I will say that when it comes to his observations and experiments, the size of his studies would play a part in his conclusions. I wonder how many mice he actually used in order to find out that” the serotonin activated the neuron through the 5H1A receptors”(wustl.edu), but I think in this case it would not really matter because the body of a mouse can not really be any different from another when it comes to certain things such as the neurons and all. Also, since this was a controlled experiment Dr. Chen had a say in everything that when on, what he changed and what he did not, that is also why third variables can be ruled out as well, because the possibility of something else being the cause of the activation is very slim to none. Overall like I said I believe these observations and experiments were conducted very well, and I did learn more about why people itch.
http://news.wustl.edu/news/Pages/22023.aspx
https://news.wustl.edu/news/Pages/27606.aspx
I agree with you that this date can not be caused by reverse causation, it just wouldn’t make sense. However I do believe that there is a chance that a third variable is affecting the data. Even though the mice were bred in order to be used for this experiment there is no way to determine wether any of the mice had a mutation in their genome contributing to the collection of data recorded. Just based off personal experience I know that when I scratch an itch it does sometimes get “itchier” but other times is does disappear entirely. Why is this? If Dr. Chen is correct in that the release of serotonin is what causes itches to be perceived by the brain as more intense why does scratching erase them sometimes and other times not? Each and every time you have an itch serotonin should be released from the glands. The experiment itself was well conducted, I just don’t think you can rule out the possibility of third variables. Some variable “Z” could, even if not easily, make this data become unreliable and since Dr. Chen conducted the experiment by himself we don’t know how many times this was proven to be accurate. It could be a case of the file drawer problem.