Dopamine, adrenaline and noradrenaline, the three main catecholamines , are some of the most relevant neurotransmitters for our nervous system. In this article we will analyze the chemical properties and functions of each of these catecholamines, as well as the common characteristics among the three neurotransmitters.

What are catecholamines?

Catecholamines are a group of neurotransmitters from the class of monoamines , to which tryptamines (serotonin and melatonin), histamine or phenethylamines also belong. Dopamine, adrenaline and noradrenaline are the three main catecholamines.

On a chemical level these neurotransmitters are characterized by the presence of a catechol (an organic compound containing a benzene ring and two hydroxyl groups) and an amine in the side chain. They are derived from the amino acid tyrosine, which we obtain through protein-rich foods such as dairy products, bananas, avocados or nuts.

The main site of catecholamine synthesis is the chromaffin cells of the adrenal medulla, as well as the post-ganglionic fibres of the sympathetic nervous system. We will describe in more detail the characteristics of the synthesis of these neurotransmitters in the following sections.

The role of these neurotransmitters is fundamental in processes such as cognition, emotion, memory and learning , motor control and regulation of the endocrine system. Likewise, noradrenaline and adrenaline are key players in the stress response.

Increases in catecholamine levels are associated with increased heart rate and glucose levels and with activation of the parasympathetic nervous system. Catecholaminergic dysfunctions can cause alterations in the nervous system, and consequently neuropsychiatric disorders such as psychosis or Parkinson’s disease.

The 3 main catecholamines

Dopamine, adrenaline and noradrenaline are very similar from a chemical point of view, but each of them has distinctive peculiarities that make it necessary to describe in detail in order to understand the functions of each of these catecholamines .

1. Dopamine

Our body transforms tyrosine into another amino acid, levodopa or L-DOPA, and this in turn is converted into dopamine. Dopamine is the most basic catecholamine, and both adrenaline and noradrenaline are manufactured from this neurotransmitter .

When found in the brain, dopamine plays a role as a neurotransmitter; this means that it participates in sending electrochemical signals between neurons. In contrast, in the blood it functions as a chemical messenger and contributes to vasodilation and inhibition of the activity of the digestive, immune and pancreas systems.

The brain pathways in which dopamine is involved, mainly the nigrostriatal and mesolimbic pathways, are related to reinforcement-motivated behaviour : their levels increase when we obtain rewards. Thus dopamine is important for processes such as learning, motor control and addictions to psychoactive substances.

The alterations in these two neural pathways cause the psychotic symptoms. Positive symptoms such as hallucinations have been associated with dysfunctions in the nigrostriatal pathway (which connects the substantia nigra to the striatum, a structure of the basal ganglia), and negative symptoms such as emotional deficits have been associated with dysfunctions in the mesocortical pathway.

The destruction of dopaminergic neurons in the midbrain substantia nigra is the cause of Parkinson’s disease . This degenerative neurological disorder is characterised above all by the presence of deficits and disturbances of a motor nature, in particular resting tremors.

2. Adrenaline

Adrenaline is generated from the oxidation and methylation of dopamine , mainly in the locus coeruleus, located in the brain stem. The synthesis of this neurotransmitter is stimulated by the release of adrenocorticotropic hormone in the sympathetic nervous system.

Adrenaline and noradrenaline, which we will talk about next, are considered the stress hormones, since when they act outside the nervous system they do not act as neurotransmitters but as hormones. They are related to cardiac and respiratory regulation and to the consumption of body resources to face environmental challenges .

Both adrenaline and noradrenaline are critical in the response to multiple types of stressors and other processes related to body activation, such as physical exercise, heat exposure, and reduced blood levels of oxygen or glucose.

3. Noradrenaline

The oxidation of adrenaline gives rise to noradrenaline, in the same way that dopamine converts noradrenaline into adrenaline and tyrosine into dopamine. Like adrenaline, it plays the role of a neurotransmitter in the nervous system and a hormone in the rest of the body.

Among the functions of noradrenaline we can highlight the cerebral alert, the maintenance of the state of vigil, the focusing of attention , the formation of memories and the appearance of sensations of anxiety, as well as the increase of blood pressure and the release of glucose reserves.

Reduced noradrenaline levels are associated with alterations in different types of learning, particularly the consolidation of long-term memories and latent learning. This function is probably due to the control of neuronal activity by noradrenaline in regions of the brain involved in learning, such as the amygdala.

On a psychopathological level, this neurotransmitter is involved in stress and anxiety disorders , major depression, Parkinson’s disease and attention deficit hyperactivity disorder.

Bibliographic references:

  • Kobayashi, K. (2001). Role of catecholamine signaling in brain and nervous system functions: new insights from mouse molecular genetic study. Journal of Investigative Dermatology Symposium Proceedings, 6(1): 115-21.
  • Zouhal, H., Jacob, C., Delamarche, P. & Gratas-Delamarche, A. (2008). Catecholamines and the effects of exercise, training and gender. Sports Medicine, 38(5): 401-23.