By: Mehar Sighat
We’ve all heard of anesthesia before, or at least seen it in our favorite shows. When a patient has to get a surgery, anesthesia is used to prevent them from feeling pain and blocks their movement. Anesthesia is used in a variety of operations, and many different anesthesia work in different ways.
There are three main types of anesthesia that affect patients differently when they are undergoing treatment. The type that you are given is dependent on the nature of the procedure, and also your personal health, including any existing or past conditions, allergies, etc. that may affect you. The first type of anesthesia is called general anesthesia, which is when the patient is unconscious and feels nothing. This is the type that we are usually most familiar with and think of when we hear about anesthesia, and is administered through an IV. The second type is local anesthesia, which is when the patient is wide awake. Yes, it is possible to be awake while under anesthesia, and we’ll talk about how in the scientist’s experiment! In this type of anesthesia the medicine is given to numb a small area, usually where the surgery is happening. Finally, regional anesthesia is another type where the patient is awake, but parts of the body are asleep, and the medicine is injected.
Because the results of each type of anesthesia are different, the effects that they have on the brain are different as well. The exact way they affect the brain is a mystery to most, and actually to scientists as well! It is known that anesthetic weakens the transmission of electrical signals between neurons, but how does that work?
In 2020, some scientists at the Okinawa Institute Of Science and Technology (Graduate University) conducted an experiment to understand exactly what happens in the brain during anesthesia. Using a common general anesthetic called isoflurane and rat brain slices, they studied what happens when electrical signals at different frequencies are induced, and how the anesthetic affects these signals.
Normally, communication in the brain occurs via neurotransmitters which are messengers that send signals between cells. Isoflurane was tested on the rat brains, and was found to have a strong effect on blocking transmission. However, it was also found that the isoflurane (anesthetic) did not block all of these signals equally, but rather had stronger effects on high frequency impulses and lower effect on low frequency impulses. But what do the frequency of impulses have to do with our bodies? Well, the higher frequency impulses are required for functions like movement and cognition, and lower frequency ones are for breathing. This is why you are able to breathe while under anesthesia, but not able to move or feel pain.
These are the effects of isoflurane, but to fully understand how this anesthetic works, we must consider the underlying mechanisms that are targeted by it to “weaken synapses” in a way that is dependent on frequency.
To understand these effects, there are some terms that need to be considered. Transport vesicles are used to move materials, like proteins and other molecules from one part of a cell to another. When the scientists continued their experiment, they hypothesized that isoflurane could block the process of vesicle release either directly (by blocking the process of vesicle release by exocytosis) or indirectly (blocking vesicle recycling, where vesicles are reformed by endocytosis). Exocytosis is a form of transport in which a cell transports molecules, and endocytosis is the uptake of extracellular material or membrane proteins by the cell membrane. By experimenting using electrical charges, these scientists found that isoflurane only affected vesicle release by exocytosis, which is the key to its anesthetic properties.
The blocking of exocytic machinery is what decreases current or voltage in a neuron, and affects higher frequency actions such as movement and cognition.
References:
Endocytosis. (n.d.). Retrieved from https://www.sciencedirect.com/topics/medicine-and-dentistry/endocytosis#:~:text=Endocytosis refers to the process,complex required for transport) pathway.
Isoflurane. (n.d.). Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/Isoflurane#:~:text=Isoflurane is a fluorinated ether,in disruption of neuronal transmission.
Scientists unveil how general anesthesia works. (2020, April 27). Retrieved from https://www.sciencedaily.com/releases/2020/04/200427125200.htm
Types of Anesthesia. (n.d.). Retrieved from https://www.uclahealth.org/anes/types-of-anesthesia
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