Human Brain & Mind
  • Acetylcholine

    Acetylcholine is perhaps the best-understood neurotransmitter in medicine. Acetylcholine" is made from choline which can be synthesized in the liver, although choline is often available in the diet and can be supplemented. The parasympathetic system uses acetylcholine as the neurotransmitter and is found everywhere in the body. For example, acetylcholine sends signals to muscle cells to contract. In the brain, acetylcholine has arousal functions in the right amounts but tends to cause depression in overdose. Alzheimer's disease is associated with declining levels of acetylcholine and degeneration of neurons which use this neurotransmitter.

    Increasing acetylcholine activity arouses thinking, memory, and computational abilities, but too much may make us feel depressed. Several antidepressant drugs block acetylcholine circuits and, if taken in overdose, produce stupor and coma by acetylcholine blockade. Physostigmine is a drug which works like acetylcholine and awakens the comatose patient immediately, although the effect is short-lived and must be repeated. The administration of choline, the acetylcholine precursor may improve memory but too much may also produce fatigue or depression. A spontaneous experiment in neurochemistry occurred when two students reported to an emergency room with marijuana intoxication and were given physostigmine intravenously. The attending physicians thought that they would be aroused from their stupor. Instead, they both experienced a prompt and profound depression with thoughts of suicide. After the experience, they expressed new empathy for those who feel suicidally depressed. The combination of marijuana and increased acetylcholine circuit activity is a formula for instant despair.

    Smoking increases nicotine levels in the brain with initial stimulation of acetylcholine circuits and later blockade. This dual action produces the typical biphasic response of an addictive drug with initial psychomotor stimulation followed by inhibition. The drive to smoke is essentially a drive to maintain brain nicotine levels. Nicotine is accompanied by a complex of toxic chemicals including carbon monoxide, benzene, and polycyclic hydrocarbons which can depress brain function. Smokers cannot expect to have clarity of consciousness, nor stable moods.

    Food-related symptoms are generated by acetylcholine mechanisms, especially nausea, vomiting, belching, cramps, defecation, sweating, and runny nose. Nicotine mimics some the actions of acetylcholine and even veteran smokers who chew nicotine gums for the first time may get these effects

    Drugs which block acetylcholine activity are popular in medicine and have many uses. .Atropine is the prototype and along with related compounds has been used in medicines to treat upset GIT function. Atropinic drugs reduce secretions and block crampy abdominal pain from vigorous contractions of intestinal smooth muscle. Too much atropine and you are dry-mouthed, constipated, and have trouble urinating; you may also have trouble thinking and remembering. In the lateral hypothalamus, acetylcholine is the transmitter of predatory aggression and prey-killing. Atropine tends to block this form of aggressive behavior. It is interesting to note that some antidepressant drugs have strong atropinic activity. Predatory aggression is different from territorial aggression which is organized by noradrenalin circuits (fight and flight). Drugs which block this activity (beta-blockers) have found many medical applications including lowering blood pressure, preventing migraine, calming racing hearts, and reducing anxiety and aggression.
    (Induction of severe depression by physostigmine in Marajuana intoxicated individuals. Br. J. Addiction 1973; 68: 321-325}

  • You are viewing the Brain Mind Center at Alpha Online. Understanding the human brain is essential to become a well-informed, modern citizen.
    Stephen Gislason MD is the author of the Human Brain. 2018 edition. 238 Pages.

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