Noradrenaline (neurotransmitter): definition and functions

For many, it is known that the functioning of the human brain is based on the transmission of bioelectric signals.

This transmission involves the presence of a series of elements that transmit information from one neuron to another, these elements being neurotransmitters. There are a large number of these substances, of very different types, causing different reactions depending on their composition and where they are received. Among these substances, in this article I will talk about norepinephrine.

Definition of norepinephrine

The substance known as norepinephrine is a neurotransmitter and hormone that works in several places in the human body.. It is a catecholamine, a group of substances made up of norepinephrine, dopamine and adrenaline that come from tyrosine and together with serotonin, acetylcholine, glutamate, glycine, opioids, anandamide and GABA make part of the main neurotransmitters in the brain.

At the cerebral level, this substance has an excitatory effect, although some of its receptors have an inhibitory function.. It participates as much in the transmission of messages between areas of the brain as outside, having a large participation in the sympathetic nervous system.

Likewise, norepinephrine not only acts as a neurotransmitter, but also functions in the endocrine system, being produced both in the brain and in the adrenal system.

Synthesis of noradrenaline

As we mentioned, norepinephrine is generated by the breakdown of tyrosine. This degradation of this substance passes through tyrosine, dopa, dopamine, noradrenaline and adrenaline, thus being a derivative of dopamine.

The synthesis of norepinephrine occurs especially in the brain nucleus known as the locus coeruleus or blue nucleus. From this region and other neighboring brain regions, brain connections are projected with locations in the brain as relevant as the cerebral cortex, limbic system, thalamus, and hypothalamus.

Out of the brain norepinephrine is also produced by the endocrine system, being generated by the adrenal glands.

his receivers

Norepinephrine acts on different types of receptors called adrenergic receptors in neurons. They are mainly metabotropic receptors, that is, norepinephrine binds to receptors which, by binding to the neurotransmitter, activate the G protein and cause other substances to act as second messengers.

Its basic receptors are the Alpha 1, Alpha 2, Beta 1, Beta 2 and Beta 3 receptors. Alpha 2 receptors are inhibitory, but the others have an excitatory effect when they act on the nervous system.

Norepinephrine degradation

As with serotonin, catecholamines such as norepinephrine are degraded by the enzyme monoamine oxidase also known as MAO, as well as by catechol-O-methyltransferase or COMPT. These enzymes are responsible for controlling the presence of excess neurotransmitters, eliminating.

Main functions of this neurotransmitter

Norepinephrine is a neurotransmitter that works in virtually all areas of the brain, as well as a hormone in the endocrine system (common in this class of substances).

In this way, its functions are multiple and varied. Here are some of the main.

1. Attention management

norepinephrine has a special implication in maintaining attention, Causing excitatory activation in the cerebral cortex which facilitates monitoring of the environment around us. Thus, the brain is able to select relevant information and separate it from irrelevant information to improve its performance when performing goal-oriented tasks. This excitement is achieved by the action of norepinephrine in the amygdala, among others.

2. Maintain vigilance and awareness

Linked to the previous point, another of the elements in which norepinephrine participates is the maintenance of wakefulness and the level of consciousness, by its mainly excitatory action in the cerebral cortex. Thus, a decrease in the levels of this neurotransmitter can cause drowsiness and difficulty acting on specific stimuli.

Thus, this neurotransmitter intervenes on the way we experience our own consciousness and subjectivityBut it is also noticeable in objective aspects, such as how we manage our attentional focus and, therefore, how we behave when performing tasks. The two processes are linked, for there can be no management of attention without awareness.

3. Influence on the cardiovascular system

The involvement of norepinephrine is not limited to the transmission of messages to the brain, but also has an effect on the heart muscles. Specifically, it works by increasing heart rate and vascular tone, producing an increase in blood pressure. Decreased levels of norepinephrine can cause hypotension, bradycardia and hypothermia.

This is one of the ways that norepinephrine works on our body through the autonomic nervous system, which is responsible for performing automatic activities related to real-time survival.

4. Fight / flight response.

Another of its functions carries it out mainly in the nucleus synthesizes that it, the locus coeruleus noradrenaline is primarily responsible for maintaining the fight-and-flight response. In this sense, it produces an increase in blood flow to the muscular system, allowing action and promoting motor responses which in many situations can get us out of dangerous situations.

5. Motivation

Norepinephrine has a consistent effect on motivational and energetic state, Actively participate alongside dopamine in the regulation of learning, memory and the sense of reward. In this way, this neurotransmitter helps our actions to have a vector, a directionality marked by short, medium and long term goals.

6. Mood regulation

Low levels of norepinephrine have been consistently linked to depressive states, Being in fact one of the hypotheses studied that depression is caused by a deficit of synthesis and presence in the cerebral synapses of this substance. This is consistent with efficacy and the fact that sleep deprivation (which as we have seen is related to norepinephrine levels) performed in a controlled manner can in some cases be effective in reducing depressive symptoms.

The role of norepinephrine has also been considered in the treatment of depression. A clear example of this is the cases of major depression, in which drugs such as serotonin and norepinephrine reuptake inhibitors can be found with very high efficacy, similar to SSRIs. These psychotropic drugs work by preventing norepinephrine and serotonin available at synapses from being reincorporated into the neuron, thus prolonging their presence and effect at the synapse.

7. Stress, aggression and sexual behavior

Norepinephrine has also been shown in several studies to be related to these three elements, Being considered a hormone that actively participates in the condition known as stress due to its action on the sympathetic nervous system.

In the case of sexual behavior, this hormone is involved in the sensation of pleasure during sexual intercourse, but also plays an important role during the birth of a new creature, speeding up contractions and participating in the reflex of expulsion of the new- born.

Bibliographical references:

  • Brunello, N. i Ragacni, G. (1998). Justification for the development of norepinephrine reuptake inhibitors. Hum Psychopharmacol; 13 (suppl. 1): S13-S20.

  • Hall, JE and Guyton, AC (2006). Manual of medical physiology. 11th edition. Philadelphia, Pennsylvania: Elsevier.

  • Martín, AM and González, FJA (1988). Compendium of psychoneuropharmacology. Diaz de Santos editions.

  • Rang, HP (2003). Pharmacology. Edinburgh: Churchill Livingstone.

  • Tanaka, M. et al. (2000). The norepinephrine systems in the hypothalamus, amygdala, and locus coeruleus are implicated in provoking anxiety: background studies.

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