Kinda like the Mob of your body, Neurotransmitters get things done and done fast. You may not have heard the term before, but you may have heard their names; names like Serotonin, Dopamine, Adrenaline, and Endorphins (a class of neurotransmitters)
What are they? What do they do? Where do they come from?
The answer all has to do with chemistry, which makes it complicated.
(I am not an organic chemist. I’m not even a chemist.)
Simply defined, a neurotransmitter is an endogenous chemical– one made inside the body– that carries signals from one neuron to another. Hank Green explains that bit in this youtube video here:
So you get the gist of it. (Absolutely counting on ya’ll to watch that video.)
Neurotransmitters, as already stated, are endogenous chemicals, made in the body through specific chemical pathways. Serotonin, for example, is synthesized from the amino acid Tryptophan, and Dopamine is synthesized from the amino acid Tyrosine. This isn’t an organic chemistry blog so I won’t go into further details…
(I am not an organic chemist.)
Neurotransmitters are found all over the body– because where there are nerves, there are neurotransmitters. Unlike hormones, which can be made in special, centralized glands and sent throughout the body, neurotransmitters are made by the cells that use them. All the serotonin made in your gut stays in your gut, and all the serotonin made in your brain stays in your brain. Many are too large a chemical to pass through the blood-brain barrier, in fact. (youtube video)
In order to make adequate amounts of neurotransmitters, we must intake a certain level of amino acids in our diets. We’ll use Serotonin and Dopamine as an example once more.
Serotonin is made from the amino acid Tryptophan. Tryptophan is one of the nine essential amino acids– So named because we lack the ability to make them ourselves and must get them from diet and they also are vital to protein synthesis in our bodies. Luckily, Tryptophan is a wildly popular chemical among other lifeforms, so as long as you have a diet of whole foods, like seeds/nuts, cheeses, red meats, poultry, fish, oats, and lentils, you’re likely golden. A full list can be found here. Tryptophan is used for more than just Serotonin synthesis in humans, and I’ll be covering that another time.
Dopamine is made from Tyrosine, which can be acquired one of two ways, either through dietary intake, list of foods here, or it can be synthesized in the liver from another essential amino acid, Phenylalanine. List of foods here.
Disruption of desired neuron activity can occur when neurotransmitter levels are depleted– either through dietary, environmental, disease, or genetic factors– the neurons are damaged–trauma, inflammatory activity, hypoxia, or toxins present– or through receptor regulation.
Receptors are regulated either up or down, which refers to the number of receptor sites on the receiving neuron. Down-regulation occurs when the receiving neuron receives prolonged exposure to an agonist- a chemical that “excites” it. The neuron weans off extra receptor sites to reduce it’s sensitivity to the agonist. This is common in long-time drug users, both of the prescribed and street kind. Up-regulation occurs when a neuron spends a prolonged amount of time with too little stimulation, so it produces more receptor sites, making it hypersensitive.
In depressed patients, it is theorized that certain receptors, such as Serotonin, Dopamine, and Nor-Epinephrine have experienced too much up-regulation and that they are down-regulated in response to anti-depressants, bringing them back to normal levels. Anti-depressants currently do this by inhibiting the reuptake of specific neurotransmitters.
Another leading theory is that long-term inflammation causes damage to the neurons, creating a form of neurodegeneration. From what I have read, it looks a bit like this:
The body, under some form of stress, produces an initial inflammatory response. This response triggers a metabolic pathway that converts Tryptophan into quinolinic acid– an excitotoxin. Quinolinic acid then over excites certain receptors and inhibits the reuptake of glutamate. This results in glutamate toxicity, which in and of itself causes cellular damage enough to kill off the cells. It also destabilizes the cytoskeleton of a cell through the modification of proteins in the cell wall, causes oxidative stress, and when inflammation occurs, quinolinic acid leads to overexcitation of the NMDA receptor, which triggers a series of events that also damage the cells and lead to cellular death. These factors result in further inflammation in the brain, perpetuating the cycle.
Therapies focusing on quinolinic toxicity are still in development but focus on modulating the pathways the body takes, hoping to either divert the formation of the acid and instead causing the body to form protective chemicals, or to suppress the formation of quinolinic acid in the first place. For more reading on quinolinic acid, check this paper out. (no paywall)
Neurotransmitters do not act in isolation either. Back to our Serotonin/Dopamine example, in patients taking Prozac, researchers found that the high levels of Serotonin produced by the drug, causes the neurotransmitter to be taken into Dopamine transporters instead of their own. (Which they believe leads to some of the very unpleasant– and potentially dangerous– side effects of SSRIs such as Serotonin Syndrome.) The underperforming of Serotonin can interact with overperforming Dopamine to produce impulsive, aggressive behavior.
Neurotransmitter action and presence is modified through the use of drugs that act either as agonists– chemicals that stimulate nerve receptors by either mimicking neurotransmitters, preventing reuptake, or increasing the production– or as antagonists– drugs that block receptor sites, speed the removal of a neurotransmitter, or slow down its production. These six things are what both prescribed and street-level drugs/supplements aim to accomplish. It’s not recommended to mix drugs/certain foods and supplements on your own– leave that to someone trained to do so. If you have any questions, talk to your doctor. You can also check Drugs.com for any known interactions.
That’s all for now! I’ll be back under the Biological section to cover Hormones, as well as specific types of Hormones and Neurotransmitters and how they affect your physical and mental health.
But you shouldn’t fret about what is yet to occur. The only way the future can harm us is by causing worry. I guarantee you’ll fell better once you’re out in the sun.
Christopher Paolini, Eragon.