Nitric oxide (neurotransmitter): definition and functions
Some of you probably think that nitric oxide is a laughing gas, better known as “laughing gas”. Well, that’s nitrous oxide.
In this article we will talk about nitric oxide, also called nitrogen monoxide or NO , which is a fat-soluble gas molecule that acts as a neurotransmitter in the brain and performs different functions within our body.
Since its discovery, nitric oxide has become one of the most studied molecules in human physiology. Studies confirm the natural ability of nitric oxide to prevent clotting, regulate inflammation, revitalize tissues, improve erectile dysfunction or kill invading microorganisms and even eradicate cancer cells.
In addition, nitric oxide promotes erection, and as a supplement is consumed in the circuits of sports training and bodybuilding, as it promotes resistance to fatigue and improves muscle development.
Characteristics of nitric oxide
This gas has aroused great scientific interest. Already in 1970, an American doctor, named Ferid Murad, noticed that the nitrates used when people suffer from chest pains or cardiovascular problems release nitric oxide, because this substance has a dilating effect on the blood vessels and relaxes the muscle layer in the endothelium .
A few years later, in 1987, studies confirmed that the human body produces nitric oxide, prompting research into how this compound is formed, what it does and what its functions are within the human body. In 1998, the authors of these discoveries, Robert Furchgott, Ferid Murad and Louis J. Ignarro, received the Nobel Prize.
How Nitric Oxide is Synthesized
Nitric oxide is synthesized from the protein amino acid arginine and L-citrulline , a non-protein amino acid, thanks to the action of an enzyme called nitric oxide synthase (NOS). In addition, the presence of oxygen and a coenzyme (an organic molecule that binds to the enzyme), the reduced nad-phosphate (NADPH), is necessary for the synthesis to take place. In most living beings NO is produced in different types of cells.
- Do you want to know the types of cells that exist in the human body? You can do so by visiting our post: “Main Cell Types of the Human Body”
Functions in our body
In addition to the studies that I mentioned earlier and which won the Nobel Prize for their authors, in the last three decades more than 60,000 studies have been carried out on this gas.
Nitric oxide performs different functions in both the central and peripheral nervous system , among which they stand out:
- Reduces inflammation and blood clotting
- It improves the performance of the immune system by defending against bacteria and fighting cancer.
- Increases recognition of senses (e.g., smell)
- Increases endurance and muscle strength and development
- Has a positive effect on gastric motility
- Improves sleep quality
- Improves memory
Nitric oxide as a neurotransmitter
Neurotransmitters are chemical molecules that send signals within the nervous system. Nitric oxide, being a gas, does not fit the classic definition of other neurotransmitters such as dopamine or serotonin.
However, this gaseous molecule performs functions as a neurotransmitter and neuromodulator .
According to authors Fernández-Álvarez and Abudara Morales, neurotransmitters should classically meet these requirements:
- Should be present in the presynapse
- It should be stored in the presynaptic terminal
- It should be released upon presynaptic nerve stimulation
- Exogenous administration of the substance would cause an identical response to that caused by presynaptic nerve stimulation, and the drugs should cause the same changes in the response caused by presynaptic nerve stimulation
- In the synapse there must be mechanisms that allow the action of this neurotransmitter substance on the post-synaptic neuron to be terminated
Since NO is a gas and its physical-chemical functions are different from other neurotransmitters, it does not meet all of the above criteria. However, this does not mean that it does not act as a chemical messenger , but that this type of transmission constitutes a particular form of transmission.
Generally, neurotransmitters are produced, stored and used when the nervous system requires them. Once they are used, an enzyme acts on them, often degrading them. In the case of NO this does not happen, as it is not produced in advance. It is synthesized at the moment it is needed.
Furthermore, unlike other neurotransmitters, it does not have a localized effect, but rather diffuses in many directions and, being a gas, can affect many cells. Therefore, although both classical neurotransmitters and NO send information, they do so in different ways.
- Would you like to know more about classical neurotransmitters? In our article “Types of neurotransmitters: functions and classification” we explain them to you.
Nitric oxide and its relationship to Viagra
Research on this gaseous compound has also concluded that nitric oxide is of paramount importance in male erection . In fact, drugs used to treat erectile dysfunction act on the nitric oxide route that allows blood flow to the male organ.
One of the best known drugs to treat this problem is Sildenafil, which you probably know by its brand name: “Viagra”. But what is the relationship between Viagra and nitric oxide? Well, when we think about having intimate relations with someone or we are in a situation where intimate stimulation takes place, nitric oxide is released in the nerve endings of the male organ .
This compound causes the relaxation of the muscles, the dilation of the cavernous bodies and the blood vessels in this area, and this relaxation allows blood to enter the arteries and, consequently, the erection. When nitric oxide moves towards the smooth muscle cells present in the blood vessels, it causes different chemical reactions by increasing the chemical messenger GMPc, this produces the dilation of the vessels that allows the flow of blood. Once cGMP has performed its function, it is degraded by the enzyme phosphodiesterase (PDE). Viagra blocks phosphodiesterase, thus preventing cGMP degradation and improving erection.