It is well known that the functioning of the human brain is based on the transmission of bioelectric 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 is a great quantity of these substances, of very diverse types, causing different reactions depending on their composition and place of reception. Among these substances, in this article I will talk about noradrenaline .
The substance known as noradrenaline is a neurotransmitter and hormone that acts in multiple points of the human body . 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 neurotransmitters in the brain.
At the brain 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, possessing a great participation in the sympathetic nervous system.
Likewise, noradrenaline does not only act as a neurotransmitter, but also exerts functions in the endocrine system, being produced both at a cerebral and adrenal level.
As mentioned, noradrenaline is generated from the degradation of tyrosine . This degradation of this substance passes through tyrosine, dopa, dopamine, noradrenaline and adrenaline, being therefore a derivative of dopamine.
Noradrenaline synthesis occurs especially in the brain nucleus known as the locus coeruleus or blue nucleus. From this and other nearby brain regions, brain connections are projected to such relevant locations 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 .
Noradrenaline acts, in the neurons, on various types of receptors that are called adrenergic receptors. These are mainly metabotropic receptors, i.e. noradrenaline binds to receptors which, when they bind 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. The Alpha 2 receptors are inhibitory, but the rest of them have an excitatory effect when they act on the nervous system.
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
Noradrenaline is a neurotransmitter that acts in virtually all regions of the brain, in addition to acting as a hormone within the endocrine system (which is common in this class of substances).
Thus, its functions are multiple and varied. Here are some of the main ones .
1. Attention focus management
Noradrenaline has a special implication in the maintenance of attention , causing an excitatory activation in the cerebral cortex that facilitates the surveillance 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 carrying out goal-oriented tasks.This excitation is carried out through the action of noradrenaline in the amygdala, among other areas.
2. Maintaining vigil and awareness
Linked to the previous point, another of the elements in which noradrenaline participates is in the maintenance of the waking state 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 acting upon specific stimuli.
Thus, this neurotransmitter intervenes in the way we experience our own consciousness and subjectivity , but it also makes itself felt in objective aspects, such as the way we manage our attention span and, consequently, how we perform when performing tasks. Both processes are linked, since there can be no attention management if there is no awareness.
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 heart muscles . Specifically, it acts by raising the 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 responsible for performing the automatic activities linked to survival in real time.
4. Fight/run response.
Another of its functions is carried out mainly in the nucleus that synthesizes it, the locus coeruleus noradrenaline is fundamentally in charge of maintaining the fight and flight response . In this sense, it produces an increase in the flow of blood towards the muscular system, allowing action and favouring motor responses that in many situations can get us out of danger.
Noradrenaline has a consistent effect on the motivational and energetic state , actively participating alongside dopamine in the regulation of learning, memory and sense of reward. 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 noradrenaline have been consistently linked to depressive states , being in fact one of the hypotheses that depression is produced by a deficit in the synthesis and presence in the brain synapses of this substance. This is consistent with the effectiveness and the fact that sleep deprivation (which as we have seen is linked to the level of noradrenaline) carried out in a controlled manner may in some cases be effective in reducing depressive symptoms.
The role of noradrenaline has also been considered in treating depression. A clear example of this is the cases of major depression, in which we can find drugs such as Dual Serotonin and Noradrenaline Reuptake Inhibitors with a very high efficacy, similar to that of the SSRIs.These psychopharmaceuticals act by preventing the noradrenaline and serotonin available at synapses from being reincorporated into the neuron, prolonging its presence and effect at the synapse.
7. Stress, aggression and sexual behavior
Noradrenaline has also shown in several studies its link with these three elements , being 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 relationships, but also has a relevant function at the time of birth of a new baby, accelerating the contractions and participating in the reflex of expulsion of the newborn.
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