The word neurotransmitter is the combination of two words neuron, which means nerve cell, and transmitter, which means transmission. If we defined it more precisely, a chemical molecule that transmits signals between nerve cells. The signal transmission from one nerve cell to the next occurs at special contact points called synapses. There is a gap between two synapses which is covered by neurotransmitters, and this gap is called the synaptic cleft.
The neurons are in contact and can communicate with each other. This is how the nerve cells in your body transmit electrical signals (excitation transmission).
How it works
It works like this in a step-by-step way.
- An electrical signal (action potential) reaches the presynaptic nerve cell. There, the neurotransmitters in membrane bubbles (which are vesicles) are stored.
- The vesicles fuse with the presynaptic membrane (fusion). As a result, the cell releases messenger substances into the synaptic gap (exocytosis).
- The neurotransmitters diffuse through the gap to the postsynaptic membrane. There are special docking points which are called receptors for the molecules. Only one specific molecule can bind to each receptor.
- So, there are specific receptors for every neurotransmitter. The molecule binds to this and thus leads to the opening of ion channels.
- Ions (charged particles) can now flow in or out through the ion channel. This creates an electrical signal again in the postsynaptic nerve cell. This can either have an excitatory (EPSP) or an inhibiting (IPSP) effect on the cell.
- Special enzymes break down the neurotransmitters in the synaptic gap. Then the presynapse can receive the transmitters again and use them again.
Examples of Neurotransmitters
Many different neuronal messengers transmit signals in your body. Here, we give you an overview of important neurotransmitters, namely acetylcholine, glutamate, GABA, serotonin, and dopamine.
Acetylcholine Neurotransmitter
The neurotransmitter acetylcholine plays an important role in both the peripheral and central nervous systems. The peripheral nervous system mediates the signals between nerve and muscle cells at the so-called motor endplate. Acetylcholine is also one of the messenger substances most common in the brain (central nervous system, CNS).
In the autonomic nervous system, acetylcholine serves as a transmitter substance in neurons of the sympathetic and parasympathetic nervous systems.
There are two different acetylcholine receptors (cholinergic receptors) that influence the action of acetylcholine:
- The nicotinic acetylcholine receptor
- The muscarinic acetylcholine receptor.
Nicotinic receptors are ionotropic receptors, so they form ion channels themselves. The muscarinic receptor, on the other hand, is a metabotropic receptor that indirectly opens ion channels.
Glutamate Neurotransmitters and GABA Neurotransmitters
It is also the precursor of the transmitter γ-aminobutyric acid (GABA). The GABA synthesis takes place through the decarboxylation (removal of the carboxyl group) of the glutamic acid. GABA, in turn, is the most common inhibitory messenger substance in the central nervous system. This means that the glutamate effect and the GABA effect are opposite. It has an excitatory effect on the brain and is the most common excitatory transmitter.
The GABA system also works via ionotropic (GABA A) and metabotropic (GABA B) receptors.
Serotonin Neurotransmitter
The neurotransmitter serotonin is important for signal transmission in the central nervous system. Serotonin has an effect on sleep, pain perception, eating, sexual behavior, and emotions. In addition, it creates a good mood and serenity.
In depression, therefore, there is often a reduced serotonin concentration. That is why dopamine and serotonin are referred to as “happiness hormones.”
Dopamine Neurotransmitter
The neurotransmitter dopamine, along with adrenaline and noradrenaline, belongs to the so-called catecholamines. Dopamine synthesis takes place primarily in the adrenal medulla and in the hypothalamus in the brain. It is an intermediate in the production of norepinephrine and epinephrine from the amino acid tyrosine.
The dopamine effect can be seen in various control processes, such as motion control and the reward system. Therefore, the death of dopaminergic neurons in Parkinson’s disease leads to a sedentary lifestyle and even immobility. Hence, dopamine drugs are used to treat Parkinson’s disease. However, dopamine cannot cross the blood-brain barrier; therefore, dopamine precursors must be used.
Sympathetic Neurotransmitter
Dopamine can also increase the effectiveness of the sympathetic system. The sympathetic is a part of the autonomic nervous system that controls the activity of many organs. The neurotransmitters acetylcholine and norepinephrine regulate their neurons. So, you can see what important role neurotransmitters play throughout the body.
Neurotransmitter Testing
A neurotransmitter test is used to determine different neurotransmitters such as serotonin, norepinephrine, epinephrine, dopamine, GABA, PEA, histamine, adrenaline, and noradrenaline in the body. These neurotransmitter tests are used to evaluate the imbalances in the neurotransmitters in the body, and they also help determine which natural remedies or medications are appropriate. The neurotransmitter tests are conducted by taking samples of urine or saliva of the patient.
Neurotransmitters and neurotransmitter metabolites available for testing:
5-HIAA
Abnormal levels have been associated with all types of depression, including persistent depressions, psychotic depression, postpartum depression, suicidal behaviors, aggression, chronic psychotropic medication use, and Parkinson’s Disease.
DOPAC
Dopamine Metabolite: Combined measurements of dopamine metabolites and dopamine have been used to evaluate the activity of dopamine neurotransmitters in dopaminergic neurons.
Dopamine Excitatory neuromodulator
Dopamine regulates epinephrine, also called adrenaline, and norepinephrine, also called noradrenaline, which is all catecholamines. Dopamine plays a crucial role in the pleasure/reward pathway (addiction and thrills), happiness, memory, and motor movement control.
Epinephrine
works as an excitatory neuromodulator neurotransmitter. Epinephrine, also named adrenaline, is derived from the amine norepinephrine. As a neurotransmitter, epinephrine plays a crucial role in our body. It regulates attentiveness and mental focus.
GABA
Gamma-aminobutyric acid, usually named GABA, its a basic function is to prevent overstimulation of the body.
Glutamate
Chronic malfunctioning of glutamatergic neurotransmitters can cause neurodegenerative disorders. Its dysfunction may be involved in many neurodegenerative diseases and memory problems such as Huntington’s disease, Parkinson’s disease, Alzheimer’s, and vascular dementia. Other neurodegenerative disorders its imbalance may cause are amyotrophic lateral sclerosis, AIDS-neurodegeneration, Tourette’s syndrome, and Korsakoff syndrome.
Histamine
Histamine works as an excitatory neurotransmitter. It is involved in the sleep/wake cycle and inflammatory response.
Norepinephrine
Norepinephrine works as an excitatory neurotransmitter. It is important for attention and focus.
PEA
Beta-phenylethylamine (PEA) works as an excitatory neurotransmitter generated from the amino acid phenylalanine.
Serotonin
Serotonin works as an inhibitory neurotransmitter. It is synthesized by enzymes that act on tryptophan or 5-HTTP.