Monoamines, as the name suggests, contain only one amino group, and this amino group is connected to an aromatic ring. An aromatic ring is shown below:
Monoamines and amino acids are connected together by the fact that every monoamine is produced from amino acids which contain an aromatic ring, such as tryptophan (which is pictured below), tyrosine and phenylalanine.
Examples of monoamines include:
- Trace amines
I’ll be discussing the first three in detail since they can appear in high concentrations, but I’ll only list the trace amines.
Histamine is primarily involved in the inflammatory response. The vast majority of histamine is not in the form of the neurotransmitter: rather, it is secreted by basophils, and their activated form, mast cells. The role that histamine plays as a neurotransmitter (as well as the hormone) is that it increases the size of the pores of the blood vessels, thereby allowing white blood cells and platelets to squeeze through and enter the areas outside the blood vessels. This is important for clearing out infections from wounds. A photographic representation of this process can be found here.
This effect, however, can be annoying if it goes wrong: it can lead to hayfever. You’ve probably experienced this at least once in your life already: that irritating runny nose and watery eyes, you’d just wish it’d go away already! Thankfully, this can be treated with anti-histamines.
The section of the compound which makes catecholamines a type of monoamine is the catechol group, which is shown alongside.There are three types of catecholamines that are abundant in the human body as a neurotransmitter: adrenaline (epinephrine), noradrenaline (norepinephrine), and dopamine. All catecholamines are derived from the amino acid tyrosine.
Adrenaline (or epinephrine for those in the States) is famous because it is the main neurotransmitter involved in the ‘fight, flight or fright’ response. It does this through the tightening (reducing the diameter) of our blood vessels and increasing our heart rate when we encounter something that scares us .It is also a very powerful medicine for treating people with conditions such as anaphylactic shock or from a heart attack because of its ability to constrict blood vessels. An example of this can be seen with people who have severe allergies: they often carry an Epi-Pen with them, like the one I’ve added below. They self-administer this when they encounter their allergen i.e. peanuts in order to prevent blood pressure from dropping too low.
Noradrenaline (or norepinephrine) is the neurotransmitter most involved in us being able to concentrate on a certain task. It acts on the sympathetic nervous system (from the brain to the organs) by increasing the contractions to the heart and affect sections of the brain such as the amygdala, in order to help us gain attention whilst we are doing something. It often works in correspondence with adrenaline to increase blood pressure.
Dopamine is the neurotransmitter involved in reward-seeking and pleasure. It is also involved in cognition. Illegal drugs such as cocaine and heroin (amphetamine) have been known to affect dopamine levels by pushing them up very high: however, there is a catch as the body quickly adapts to the new level and in order to achieve the same high again, a higher dose must be taken. This also affects your sense of mood: once your body adapts to the new high levels, it is very difficult to achieve the same amount of pleasure or even normalcy again, which unfortunately traps people in the cycle of addiction.
There are two main types of tryptoamines: melatonin, which I talk about briefly in Glands in the Brain and serotonin. Both of these contain an indole ring structure, which is shown here. I won’t go into too much detail here about melatonin, but I will attempt to go over serotonin in more detail. Funny fact: tryptamines are the chemicals involved in magic mushrooms!
As I mentioned in the Brain Anatomy section, melatonin is secreted by the pineal gland and is responsible for controlling our diurnal rhythm. It is also capable of suppressing your libido by counteracting the effects of FSH and LH, which I’ve already mentioned in Pituitary Gland=Master. It also was discovered that melatonin acts as an antioxidant: it captures free radicals.
Don’t worry, be happy!
Serotonin is the main neurotransmitter involved in our moods; specifically, the highs that we experience. A lack of serotonin, therefore, can lead to depressive moods and makes some us have to take antidepressants such as SSRIs (selective seretonin reuptake inhibitors), either temporarily or for a lifetime.
As well as moods, serotonin helps control our appetite and our sense of sleep. This makes sense, because the vast majority of serotonin gets stored in our gut: particularly, the enterochromaffin cells. The serotonin actually helps the gut to contract around the food and help push it along.
There is an extensive list of trace amines, and they include the following:
- B-PEA (beta-phenylethylamine)