Norepinephrine (neurotransmitter): definition and functions

It is known to many that the operation of the human brain it is based on the transmission of bioelectric signals.

This transmission implies the presence of a series of elements that transmit information from one neuron to another, these elements being the neurotransmitters. There is a large amount 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 norepinephrine.

Defining norepinephrine

The substance known as norepinephrine is a neurotransmitter and hormone that acts at multiple points in the human body. It is a catecholamine, a group of substances configured by norepinephrine, dopamine Y adrenalin which come from tyrosine and that together with serotonin, acetylcholine, glutamate, glycine, opioids, anandamide and GABA they are part of the main brain neurotransmitters.

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, having a great participation in the sympathetic nervous system.

Likewise, norepinephrine does not only act as a neurotransmitter, but also exerts functions in the endocrine system, being produced both at the brain and adrenal level.

Synthesis of norepinephrine

As we have mentioned, norepinephrine is generated from the breakdown of tyrosine. Said degradation of this substance goes through tyrosine, dopa, dopamine, norepinephrine and adrenaline, thus being a derivative of dopamine.

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

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

Your receivers

Norepinephrine acts, in neurons, in various types of receptors that are called adrenergic receptors. These are mainly metabotropic receptors, that is to say that norepinephrine binds to receptors that, upon their union with the neurotransmitter, activate the G protein and they 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 rest of them have an excitatory effect when they act on the nervous system.

Norepinephrine breakdown

As with serotonin, catecholamines such as norepinephrine are degraded by the enzyme monoamine oxidase also known as MAO, as well as 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).

In this way, its functions are multiple and varied. Let's see below some of the main.

1. Attentional focus management

Norepinephrine has a special implication in the maintenance of attention, causing an excitatory activation in the cerebral cortex that facilitates the surveillance of the environment that surrounds us. Thus, the brain is able to select relevant information and separate it from irrelevant to improve its performance when carrying out goal-oriented tasks. This excitation is carried out by the action of norepinephrine in the la amygdala, among other areas.

2. Maintenance of wakefulness and consciousness

Linked to the previous point, Another of the elements in which norepinephrine participates is in the maintenance of the waking state and the level of consciousness, due to its mainly excitatory action on the cerebral cortex. Thus, a decrease in the levels of this neurotransmitter can cause drowsiness and difficulties in acting when faced with specific stimuli.

Thus, this neurotransmitter intervenes on the way in which we experience our own consciousness and subjectivity, but it is also noticeable in objective aspects, such as the way in which we manage our attention focus and, consequently, in what way we perform when performing 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 norepinephrine 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 norepinephrine can cause hypotension, bradycardia, and hypothermia.

This is one of the ways in which norepinephrine exerts a function on our body through the autonomic nervous system, in charge of carrying out the automatic activities related 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 norepinephrine is fundamentally in charge of maintaining the fight and flight response. In this sense, it produces an increase in blood flow to the muscular system, allowing the acting and favoring motor responses that in many situations can get us out of situations of danger.

5. Motivation

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

6. Mood regulation

Low norepinephrine levels have been consistently linked in depressive statesIn fact, one of the hypotheses considered is that depression is produced by a deficit in the synthesis and presence of this substance in the 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 of norepinephrine) performed in a controlled manner may be effective in some cases to reduce depressive

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

7. Stress, aggressiveness, and sexual behavior

Norepinephrine has also shown its link with these three elements in various studies, 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 intercourse, but they also have a function relevant at the time of the birth of a new creature, accelerating contractions and participating in the expulsion reflex of the newborn born.

Bibliographic 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 edition. Philadelphia, Pennsylvania: Elsevier.

• Martina. M. & González, F. J.A. (1988). Compendium of psychoneuropharmacology. Editions 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.