- Acetylcholine: structure, synthesis and degradation
- How does acetylcholine work and what does it do?
- The use of acetylcholine in medicine
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Acetylcholine is a neurotransmitter that affects heart and gastrointestinal function, but is also associated with memory processes. Due to the fact that the actions of acetylcholine in the body are very wide, drugs affecting this neurotransmitter are used in many areas of medicine - they are prescribed to patients by both neurologists, ophthalmologists and internists.
Acetylcholineis one of the neurotransmitters, i.e. specific molecules necessary in the nervous system - it is thanks to the nerve cells that nerve impulses are sent. Acetylcholine is important primarily because it is present in both the central and peripheral nervous systems, but it is also found in the somatic and autonomic nervous systems.
It is worth adding that acetylcholine was the first neurotransmitter discovered by scientists. In 1914, the discovery was made by the English physiologist Henry Dale, and a few years later - in 1921 - of German origin, Otto Loewi introduced the functions of acetylcholine to the medical world. The discoveries of both men turned out to be so important for science that in 1936 they were awarded the Nobel Prize for them.
Acetylcholine: structure, synthesis and degradation
Acetylcholine is an ester of acetic acid and choline. It is created within the so-called cholinergic neurons (these are those populations of nerve cells that secrete acetylcholine within their endings), where the neurotransmitter is produced from choline and acetyl coenzyme A with the participation of the enzyme choline acetyltransferase. The resulting acetylcholine molecules are then accumulated in synaptic vesicles, and when the nerve cell depolarizes, they attach to the presynaptic terminals and acetylcholine is released into the synaptic space. When a neurotransmitter reaches the postsynaptic terminal, it binds to its receptor and exerts its usual actions.
Secreted from nerve endings, acetylcholine does not stay outside of nerve cells for a long time - it is broken down quite quickly by the enzyme acetylcholinesterase. It is in this reaction that, among others, choline, some of which is transported back into the interiornerve cells - the choline recovered in this way is later used to produce other acetylcholine molecules.
How does acetylcholine work and what does it do?
The functions of acetylcholine depend both on where this neurotransmitter acts and the type of receptor it will attach to. Acetylcholine has two types of receptors to which it attaches: the first are nicotinic receptors (present in the ganglia of the autonomic system and within the neuromuscular junction), the second are muscarinic receptors (located in many different tissues, including cells smooth muscles, in various structures of the brain and in the endocrine glands and cells of the heart muscle).
In the central nervous system, acetylcholine affects memory processes and the ability to concentrate attention. The function of this neurotransmitter is also to keep us awake, and acetylcholine is also important in various learning processes. This relationship enables communication between various areas of the central nervous system - in this case, acetylcholine is secreted by the so-called interneurons and it is especially important in the case of the basal ganglia.
In the peripheral nervous system, acetylcholine is especially important for muscle cells - this neurotransmitter is secreted within the neuromuscular plates. The acetylcholine released from nerve cells, when it binds to the receptors present on myocytes, causes contraction of the given muscle groups.
Acetylcholine is also extremely important for the autonomic nervous system. It is a neurotransmitter that is secreted by all preganglionic fibers in this part of the nervous system. Moreover, it is released by postganglionic fibers belonging to the parasympathetic system. Acetylcholine, secreted from the parasympathetic nervous system, exerts many different activities, including:
- drop in blood pressure;
- stimulation of peristalsis in the digestive tract;
- slow heart rate;
- contraction of the lumen of the respiratory tract;
- constriction of the pupils;
- stimulation of secretion by various glands (including salivary glands).
Acetylcholine: related diseases
Due to the fact that acetylcholine is an extremely important neurotransmitter, pathologies associated with it can lead to many different disease entities. An example of this is myasthenia gravis, in which patients develop antibodies to acetylcholine receptors. Eventually, as a result of this phenomenon, it diminishesthe number of these free structures within the muscle cells, so that patients experience various symptoms of myasthenia gravis, including primarily muscle weakness. Under normal conditions, the binding of acetylcholine to the receptor leads to muscle contraction - when the receptors are blocked by antibodies, the neurotransmitter has basically nothing to attach to - muscle cells are then simply impaired in their ability to work.
Another problem in which acetylcholine disorders may contribute to the pathogenesis is Alzheimer's disease. According to some hypotheses, this neurotransmitter deficiency is associated with this unit - it is for this reason that patients suffering from Alzheimer's disease are given drugs that block the activity of the enzyme that breaks down acetylcholine, i.e. acetylcholinesterase inhibitors (thanks to this, the amount of this neurotransmitter in the nervous system is increased). Some researchers, due to the limited effectiveness of these drugs, deny the fact that in Alzheimer's disease there is indeed a deficiency of acetylcholine in patients.
The use of acetylcholine in medicine
In medicine, both substances that exert acetylcholine-like effects, as well as agents that have a completely opposite effect are used. In the first of these cases, we are talking about parasympathomimetic drugs. These include substances such as, for example, pilocarpine (which leads to constriction of the pupil and is used in glaucoma) or the aforementioned acetylcholinesterase inhibitors (actually indirect parasympathomimetics).
Preparations with a different effect are parasympatholytic (cholinolytic) drugs. They have the opposite effects to acetylcholine and include them, inter alia, ipratropium bromide (used to expand the airways) or atropine (used in bradycardia, i.e. slow heart rate).
The action of botulinum toxin (more probably known as botox) is also associated with acetylcholine. This substance blocks the release of acetylcholine from the nerve end. Although botulinum toxin is most associated with treatments in the field of aesthetic medicine, it has many more applications in medicine - its effect on acetylcholine is used, among others, in the treatment of blepharospasm, torticollis or excessive sweating.
Some patients are interested in the so-called nootropic (procognitive) drugs. Some of these substances affect the amount of acetylcholine in the structuresof the nervous system and thus these preparations would improve the cognitive functions of people who use them - typically people who care about the best memory abilities or increasing the level of concentration are interested in nootropic drugs. However, the effectiveness of such measures seems to be quite controversial, and therefore it is recommended to approach them with caution and caution.
Sources: 1. Acetylocholine. Neuroscience 2nd Edition, on-line access: https://www.ncbi.nlm.nih.gov/books/NBK11143/2. Materials of the Encyclopaedia Britannica, on-line access: https://www.britannica.com/science/acetylcholine3. Materials of The University of Texas, on-line access: http://neuroscience.uth.tmc.edu/s1/chapter11.htmlAbout the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.