Without neurotransmitters, there would be neither memory nor emotions. There are dozens of these brain chemical messengers, but six of them lead the way and can be modulated by food. Find out why we are what we eat!
To find out how molecules can act on alertness, memory, feelings of well-being, or stress, a quick visit to the brain is essential. To understand why certain brain operations become dull over time, a quick tour of the cells is essential.
The brain is isolated from the rest of the body by an envelope called the blood-brain barrier. It is very selective and does not allow any substance to enter the brain.
The brain is made up of one hundred billion nerve cells called neurons. Neurons are traversed at all times by electrical discharges, which are the means that many living beings have found to convey information. A neuron is designed in such a way that it can detect small electric currents and transmit them to other cells. It is this flow that determines the thought process.
Like other cells in the body, a neuron has a membrane and a nucleus. But unlike other cells, it is extended by long filaments called dendrites and axons: in general, several dendrites and a single axon. The signal is received at the dendrites, it is sent to the cell, and it triggers (or not) a relay signal that travels along the axon to the dendrites of other neurons.
The length of an axon is variable, but it can exceed one meter. For example, we have nerve cells at the foot intended to transmit information to the center of balance in the brain. Very long axons extend these nerve cells. The information sent to the brain must be as fast as possible to prevent us from falling while walking.
But how can neurons transmit information?
How the message is conveyed
At the end of the axons, there are small protrusions called synaptic terminals. These terminals are linked to the dendrites of other neurons. In reality, the synaptic terminals are not directly in contact with the dendrites.
Between them extends a tiny space called a synapse. The synapse is the precise place where the signal passes from one cell to another.
To convey this signal through the narrow space of the synapse, the synaptic terminal of a neuron will most often use a substance that it previously stored in small vesicles and release it in the space which separates it. This substance is called a neurotransmitter. The neurotransmitter is nothing but a chemical messenger. He waits in his vesicles for an electrical impulse, after having traversed the axon, to propel him to the other side of the synaptic space.
It then crosses the small distance, which separates it from the wall of a dendrite. There, it is picked up by special housings on the surface of the dendrite, which is called receptors.
The arrival of the neurotransmitter in the receptors triggers a series of biochemical reactions that give rise to an electrical signal. Thus propagate the signals that allow life.
Neurotransmitters are essential for our well-being because they are the ones that allow the brain to communicate with the rest of the body. Without them, there would be no muscle contraction - voluntary or involuntary. There would be no breathing. The hormones would not be delivered. Without them, we would be unable to see, think, understand, remember, experience joys, or sorrows.
This is, for example, the case with glutamic acid, or even glycine, two amino acids found in proteins. They are a bit the illustration of the old adage, "we are what we eat.”
Others have slightly more complex structures, and the brain has to combine several substances to make them. And bring in other substances such as minerals or vitamins so that the chemical reactions necessary for manufacturing take place normally. These slightly more sophisticated neurotransmitters are made directly by neurons. They are then, as we have seen, stored in vesicles.
Neurotransmitters have multiple functions, and it is difficult to assign each one a specific role in this or that aspect of our behavior. However, when the action of neurotransmitters is disturbed, we often see behavioral disorders appear, such as anxiety, depression, and even aggressiveness. However, it is now possible to measure in the urine or blood the degradation products of these neurotransmitters, which is to say the trace of their action in the brain. These dosages allow having a better idea of the relations between such a neurotransmitter and such a behavioral trait.
The neurotransmitters that follow are the most important in the brain for the control they exert over neurons. They are also the most studied, and those who are most often the target of natural molecules (nutrition) or synthetic molecules (drugs).
Acetylcholine is the only major neurotransmitter that is not made from an amino acid. It is synthesized from a food substance, choline, and the active form of pantothenic acid (vitamin B5).
Acetylcholine is a "do-it-all" neurotransmitter that is involved in the control of movement, including the pulse, as well as a multitude of physiological functions. It is also the chemical messenger of memory. The regions of the brain that offer the highest density of neurons using choline are those that degenerate into Alzheimer's disease. Even in healthy people, we know that with age, the body produces less acetylcholine. This situation is at the origin of memory problems, lack of concentration, forgetfulness.
Dopamine is a neurotransmitter synthesized by certain nerve cells from tyrosine, an amino acid (a component of proteins in food).
In humans, the drop in activity of dopaminergic neurons in a certain region of the brain (the black substance - striatum axis) leads to a decrease in spontaneous movement, muscle stiffness, and tremors. It's Parkinson's disease.
Noradrenaline: carrot and stick
Norepinephrine is synthesized by certain neurons from the same amino acid that is used to make dopamine.
Noradrenaline modulates attention, learning and facilitates the response to reward signals: the greater the noradrenergic sensitivity; the more these traits are amplified. In humans, the decrease in norepinephrine affects the acquisition of new knowledge and associations. But caffeine, which increases norepinephrine in the brain, improves the ability to perform repetitive and boring tasks. The administration of tyrosine to depressed patients increases the secretion of norepinephrine. This treatment improves the hedonic component of their depression.
Serotonin is synthesized by certain neurons from an amino acid, tryptophan, which enters for a small part in the composition of food proteins. In the brain, serotonin influences the activity of other neurons, most often by decreasing their frequency of discharge, inhibiting their action. In the striatum, the serotonergic neurons inhibit the dopaminergic neurons, which results in a decrease in movement. Since serotonin is used to inhibit many regions of the brain, the same regions are "uninhibited" when there is too little serotonin.
GABA (gamma-amino butyric acid) is synthesized from glutamic acid. It is the most common neurotransmitter in the brain. GABA seems to be involved in certain stages of memorization. GABA is also an inhibitory neurotransmitter, i.e., it slows down the transmission of nerve signals. Without it, neurons could literally get carried away, transmitting signals faster and faster, until the system is exhausted. GABA keeps them under control.
Adrenaline activates the body's response to a stimulus, and in general, to stress. It acts on the sympathetic nervous system and can increase the pulse, the blood pressure, improve the memory, decrease the reflexion, increase the force of muscular contraction, increase the blood flow and the respiratory capacity (by the loosening of the smooth muscles), dilate the pupils and make the hair stand up. It prepares the organism for a reaction of the "flee" or "face" type.