Neurotransmitters are substances that are synthesized within the body and that act as chemical messengers and transmit the signal from a neuron to the target cell through the synapse. There are two general types of these substances; the Excitatory and Inhibitory neurotransmitters.
How do neurotransmitters work?
When a nerve impulse arrives, neurotransmitters are released into the synaptic space and bind to receptors present in the postsynaptic cell, causing changes in the electrical excitability of its membrane.
This change in electrical excitability occurs through a temporary change in the flow of ions across the cell membrane and results in an increase or decrease in the possibility of generating an action potential in the postsynaptic cell, which is known as postsynaptic potential (PSP)
Based on the postsynaptic potential, neurotransmitters are classified into two broad types:
- Excitatory neurotransmitters – They depolarize the membrane and increase the possibility of an action potential being generated. They produce postsynaptic excitatory potential (EPSP).
- Inhibitory neurotransmitters – They keep the membrane polarized and decrease the possibility of an action potential generation. They produce postsynaptic inhibitory potential (IPSP).
What is the difference between them?
The distinction between excitatory neurotransmitters and inhibitory neurotransmitters is not absolute. The action of a neurotransmitter is produced by the effect of the union between the neurotransmitter and its receptor, but the same neurotransmitter can bind to different receptors and generate different responses.
Thus, the same neurotransmitter can be excitatory if it binds to a certain receptor and inhibitor when it binds to another receptor. There are neurotransmitters whose predominant action is excitatory, such as glutamate or epinephrine, others whose predominant action is inhibitory, such as GABA or serotonin, and others that do not have a predominant action on the other, such as acetylcholine.
The excessive accumulation of excitatory neurotransmitters can damage neurons, even kill them. This situation is known as excitotoxicity and has been observed in diseases of the central nervous system such as Parkinson’s, Alzheimer’s, Multiple Sclerosis, or Epilepsy attacks.
The three main inhibitory neurotransmitters
GABA – gamma-aminobutyric acid
GABA or gamma-aminobutyric acid is the most important of the inhibitory neurotransmitters in the nervous system. It is the most abundant of them, and it is distributed throughout the brain and spinal cord. Between 30 to 40% of the neurons in our brain exchange the neurotransmitter GABA. These neurons are called GABAergic. This substance is essential on the sensitive, cognitive, and motor plane. It also plays a vital role in stress response. It also appears to play an important role in the regulation of female hormonal cycles.
It is not surprising that GABA performs a multitude of functions due to its wide distribution and quantity throughout our central nervous system. Many of its exact functions are still not known today. Much of the current discoveries are due to research with drugs that potentiate, mimic, or inhibit the effects of GABA.
GABA levels or its activity can be altered by various conditions. For example, due to the consumption of alcohol or drugs. It has been found that after receiving high doses of GABA, a significant increase in growth hormone is noted. This hormone allows the recovery and development of muscles and also increases during deep sleep. On the other hand, certain neurological and psychiatric diseases have been associated with alterations in the functioning of GABAergic neurons and their receptors.
In summary, gamma-aminobutyric acid is known to be an inhibitory substance that helps maintain balanced brain activity.
Dopamine is one of the best-known neurotransmitters in our nervous system. It activates the pleasure and reward circuits of the brain, in addition to the sensation of calm and relaxation, among other sophisticated processes. This fascinating chemical compound is also one of the most important in regulating our behavior. In the case of dopamine, dopaminergic neurons are responsible for releasing and producing this neurotransmitter.
Dopamine is synthesized through the amino acid tyrosine and accumulates in the synaptic vesicles at the axonal terminals of dopaminergic neurons. These neurons are mainly found in a part of our brain called the substantia nigra. It is from there that these neurons spread through different pathways, each with a different function.
Serotonin is a molecule synthesized by the neurons of the central nervous system that has a role as both a hormone and a neurotransmitter since it is capable of both flowing through the blood, modifying the physiology of different organs and tissues, and regulating the activity of the nervous system.
Serotonin is produced in our brains naturally and ensures that our physiology, vital functions, and emotions are consistent with the changes we experience in the environment.
In this sense, serotonin fulfills many different functions, having an impact on body temperature, appetite, cell division, the health of the cardiovascular system, sleep cycles, and cognitive functions. Besides, it is known as the “happiness hormone” since it largely determines our mood and control of emotions.
An important aspect to mention about this neurotransmitter (and hormone) is that to synthesize it; the brain needs tryptophan, a molecule that the body is not capable of producing on its own but must come from the diet. Bananas, eggs, pasta, rice, legumes, chicken, etc., are foods rich in tryptophan.
Knowing the complexity of our neurotransmitters helps us to better understand how our brain works. This is undoubtedly essential knowledge when developing treatments or drugs that help us control possible imbalances of these substances in the different areas of our nervous system.