Monoamines: what they are and functions

Neurotransmitters are essential for our well-being. For example, thanks to them our brain communicates with other parts of the body. Monoamines are located within the neurophysiological classification of neurotransmitters.

The main characteristic of monoamines is that They are distributed throughout the entire central nervous system and also throughout the peripheral nervous system. Basically, they are neurotransmitters that have various neuromodulation functions.

Monoamines receive and release synaptic material, which contains information for each of the complex activities we perform. Despite its microscopic size, they can regulate functions such as attention, emotional states and visceral functions.

Monoamines and their function

Regulation of neurotransmitters in the monoamine group is disrupted in a variety of psychiatric disorders and, in fact, many psychotropic drugs (that affect behavior or mood) affect one or more stages of their synthesis, storage or degradation.

In this sense, some antidepressants act as inhibitors of monoamine oxidase (MAOI), an enzyme necessary for the catabolism of monoamines.

Monoamines are produced by several neuron systems in the brain. Therefore, monoamine neurons serve to modulate the function of large regions of the brain, increasing or decreasing the activity of certain brain activities.

Types of monoamines: catecholamines and indolamines

Monoamines are divided into two subclasses: catecholamines and indoleamines.. In turn, within the catecholamines, there would be three neurotransmitters: norepinephrine, dopamine and adrenaline. Within the category of indolamines there would only be serotonin.

catecholamines

All catecholamines are derived from tyrosine metabolism. The two main enzymes involved in catecholamine catabolism are monoamine oxidase (MAO) – present in nerve endings and catechol O-methyltransferase (COMT) – present in all tissues. These two enzymes are the target of many psychotropic treatments.

Dopamine (DA)

Dopamine is a neurotransmitter synthesized by certain nerve cells from tyrosine, an amino acid (a component of protein in the diet). Affects the muscle movement, tissue growth or the functioning of the immune system.

Dopaminergic networks in the brain are closely associated with exploration, vigilance, pleasure-seeking, and active punishment avoidance behaviors. Low dopaminergic activity is found in melancholic depression, characterized by a decrease in motor activity and initiative.

On the contrary, products and activities that provide pleasure, such as heroin, cocaine, sex, activate certain dopaminergic systems. Therefore, Drugs that increase dopamine, such as L-Dopa or amphetamines, also increase aggression, sexual activity, and initiative.

Adrenaline (A)

Adrenaline, also known as epinephrine, It is one of those multipurpose substances that our body uses to regulate different processes.

It is a hormone, since it travels through the blood to reach different areas of the body and fulfill its task in the most remote corners of it, but it is also a neurotransmitter, which means that it acts as an intermediary in the communication between neurons. .

Adrenaline is the hormone and neurotransmitter of situations in which we have to be alert and activated.. In other words, adrenaline organically prepares us to react quickly. In particular, its release increases when we detect a threat.

Norepinephrine (NA)

The main noradrenergic neurons are found in the locus coeruleus and the nucleus of the brainstem. that projects diffusely onto the midbrain and telencephalon. These neurons play an important role in sleep modulation.

In rats, destruction of the locus coeruleus, the seat of norepinephrine neurons, leads to a complete disappearance of fear. In humans, decreased norepinephrine affects the acquisition of new knowledge and associations. But caffeine, which increases norepinephrine in the brain, improves the ability to perform repetitive, boring, and unrewarding tasks.

The administration of tyrosine to depressed patients increases the secretion of norepinephrine. This treatment improves the hedonic component of your depression.

In conclusion, Norepinephrine appears to create a favorable terrain for arousal, learning, sociability, sensitivity to emotional cues, and sexual desire.. On the contrary, when the synthesis or release of norepinephrine is interrupted, withdrawal, detachment, demotivation, depression, and low libido may appear.

The indolamines

Indoleamines are neurotransmitters that contain an indole group. In this group are serotonin and melatonin.

Serotonin

Destruction of brain regions with a high density of serotonergic neurons leads to a disinhibition of reflective control over behavior: the animal gives way to impulses, regardless of the consequences of its actions.

When electric shocks are applied to a rat trying to obtain food, it stops trying after at most 12 trials. However, at low serotonin levels, it persists after 200 shocks.

Mice and rats usually coexist without problems in a cage. However, if their serotonin is abnormally low, the rats kill the mice. Serotonin depletion also leads to disinhibition of sexual activity.

In humans, Abnormally low levels of serotonin are usually associated with impulsive, aggressive, or even very violent behavior. This is particularly the case in violent forms of suicide.

Dr. Markus Kruesi’s team (University of Illinois, Chicago) found that a low level of serotonin in a troubled child was the best predictor of criminal or suicidal behavior.

Melatonin

Melatonin is a hormone present in the body that affects sleep.. The production and release of melatonin in the brain is related to the time of day: it increases with darkness and decreases when it is light. Melatonin production decreases with age.

Melatonin is also available as a supplement; generally in tablet form that is taken orally. Most melatonin supplements are made in a laboratory. Melatonin is commonly used for sleep disorders such as insomnia and jet lag.

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