Noradrenaline (neurotransmitter): definition and functions

We explain all the keys to understand how noradrenaline acts in our brain.

It is well known that the functioning of the human brain is based on the transmission of bioelectrical signals.

This transmission implies the presence of a series of elements that transmit the information from one neuron to another, being these elements the neurotransmitters. There are a large number of these substances, of very different types, causing different reactions depending on their composition and place of reception. Among these substances, in this article I am going to talk about noradrenaline..

Defining noradrenaline

The substance known as noradrenaline is a neurotransmitter and hormone that acts in multiple points of the human organism.. It is a catecholamine, a group of substances made up of noradrenaline, dopamine and adrenaline which come from tyrosine and which, together with serotonin, acetylcholine, glutamate, glycine, opioids, anandamide and GABA, form part of the main brain neurotransmitters.

At the cerebral level, this substance has an excitatory effect, although some of its receptors have an inhibitory function.. It participates both in the transmission of messages between areas of the brain and with the outside world, and plays a major role in the sympathetic nervous system.

Likewise, noradrenaline not only acts as a neurotransmitter, but also has functions in the endocrine system, being produced both at the cerebral and adrenal levels.

Synthesis of noradrenaline

As mentioned above, noradrenaline is generated from the degradation of tyrosine.. The degradation of this substance passes through tyrosine, dopa, dopamine, noradrenaline and adrenaline, thus being a derivative of dopamine.

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

Outside the brain, noradrenaline is also produced by the endocrine system, being generated by the adrenal glands..

Its receptors

In neurons, noradrenaline acts on various types of receptors called adrenergic receptors. These receptors are mainly metabotropic, i.e. noradrenaline binds to receptors that upon binding to the neurotransmitter activate the G protein and cause other substances to act as second messengers.

Its basic receptors are Alpha 1, Alpha 2, Beta 1, Beta 2 and Beta 3 receptors. Alpha 2 receptors are inhibitory, but the rest of them have an excitatory effect when acting on the nervous system.

Degradation of noradrenaline

As with serotonin, catecholamines such as noradrenaline 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 them..

Main functions of this neurotransmitter

Norepinephrine is a neurotransmitter that acts in practically all regions of the brain, in addition to acting as a hormone within the endocrine system (something common in this class of substances).

Thus, its functions are multiple and varied. Here are some of the main ones.

1. Attentional focus management

Norepinephrine is particularly involved in the maintenance of attention, provoking an excitatory activationIt causes an excitatory activation in the cerebral cortex that facilitates vigilance of the surrounding environment. Thus, the brain is able to select relevant information and separate it from irrelevant information to improve its performance when carrying out goal-oriented tasks. This arousal is carried out through the action of noradrenaline in the amygdala, among other areas.

2. Maintenance of wakefulness and consciousness

Linked to the previous point, another of the elements in which noradrenaline participates is in the maintenance of the state of wakefulness and the level of consciousness, due to its mainly excitatory action in the cerebral cortex. and the level of consciousness, due to its mainly excitatory action in the cerebral cortex. Thus, a decrease in the levels of this neurotransmitter can cause drowsiness and difficulties in responding to specific stimuli.

Thus, this neurotransmitter is involved in the way we experience our own consciousness and we experience our own consciousness and subjectivitybut it also affects objective aspects, such as the way in which we manage our attentional focus and, consequently, how we perform when carrying out tasks. Both processes are linked, since there can be no management of attention if there is no consciousness.

3. Influence on the cardiovascular system

The involvement of noradrenaline is not limited to the transmission of brain messages, but also has an effect on the cardiac muscles. has an effect on the cardiac muscles. Specifically, it acts by elevating heart rate and vascular tone, producing an increase in Blood pressure. A decrease in the level of noradrenaline can cause hypotension, bradycardia and hypothermia.

This is one of the ways in which noradrenaline exerts a function on our body through the autonomic nervous system, which is in charge of performing automatic activities linked to survival in real time.

4. Fight/flight response.

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

5. Motivation

Norepinephrine has a consistent effect on the motivational and energetic state, actively participating together with dopamine in the regulation of learning, memory and reward sensation.It actively participates together with dopamine in the regulation of learning, memory and reward sensation. In this way, this neurotransmitter helps our actions to have a vector, a directionality marked by short, medium and long term objectives.

6. Mood regulation

Low levels of norepinephrine have been consistently linked to depressive states.In fact, one of the hypotheses put forward is that depression is produced by a deficit in the synthesis and presence of this substance in brain synapses. This is consistent with the effectiveness and with the fact that sleep deprivation (which as we have seen is linked to the level of noradrenaline) carried out in a controlled manner can be effective in some cases in reducing depressive symptomatology.

The role of noradrenaline has also been taken into account in the treatment of depression. A clear example of this is in cases of major depression, where we can find drugs such as Dual Serotonin and Noradrenaline Reuptake Inhibitors with a very high efficacy, similar to that of SSRIs. These psychotropic drugs act by preventing the noradrenaline and serotonin available in the synapses from being reincorporated into the neuron, prolonging their presence and effect in the synapse.

7. Stress, aggression and sexual behavior

Noradrenaline has also been shown in several studies to be linked to these three elements.It is considered a hormone that actively participates in the state 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 intercourse, but it also has a relevant function at the moment of birth of a new child, accelerating contractions and participating in the expulsion reflex of the newborn.

Bibliographical references:

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

• Hall, J.E. & Guyton, A.C. (2006). Textbook of Medical Physiology. 11th ed. Philadelphia, Pennsylvania: Elsevier.

• Martín, A. M. & González, F. J. A. (1988). Compendium of psychoneuropharmacology. Ediciones Díaz de Santos.

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

• Tanaka, M. et al. (2000). Noradrenaline systems in the hypothalamus, amygdala and locus coeruleus are involved in the provocation of anxiety: basic studies.