What are neurotransmitters?

Human life activities require neural regulation, which is a complex process. Neurotransmitters are needed to play an important messenger role, that is, an important medium for transmitting signals. When studying biology in high school, we usually learn about nerve conduction in detail, so everyone must be familiar with the term neurotransmitter. If you still don’t know what neurotransmitters are, let’s learn about this knowledge below.

What are neurotransmitters?

Neurotransmitters (in English: neurotransmitter) are specific chemical substances that act as "messengers" in synaptic transmission, and are referred to as transmitters for short. With the development of neurobiology, a large number of neuroactive substances have been discovered in the nervous system.

In the central nervous system (CNS), the most important mode of synaptic transmission is neurochemical transmission. Immediately after neurotransmitters are released from the presynaptic membrane

Binding to the corresponding postsynaptic membrane receptors produces synaptic depolarization potential or hyperpolarization potential, resulting in an increase or decrease in the excitability of the postsynaptic nerve. The action of neurotransmitters can be terminated through two pathways: one is recycling inhibition, that is, the excess neurotransmitters in the synaptic cleft are recycled to the presynaptic neuron through the action of presynaptic carriers and stored in vesicles; the other pathway is enzymatic hydrolysis. Taking dopamine (DA) as an example, it is metabolized and inactivated through the action of monoamine oxidase (MAO) located in the mitochondria and catecholamine o-methyltransferase (COMT) located in the cytoplasm.

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Neurotransmitters must meet the following criteria:

1. Synthesized in neurons.

2. Stored in the presynaptic neuron and released upon depolarization

Amount at a given concentration (having a significant physiological effect).

3. When used as a drug, the exogenous molecule resembles endogenous neurotransmitters.

4. The mechanism of neurons or synaptic clefts is the clearance or inactivation of neurotransmitters. If all criteria are not met, it is called a “proposed neurotransmitter”.

Neurotransmitters in the brain are divided into four categories, namely biogenic amines, amino acids, peptides, and others. Biogenic amine neurotransmitters were the first to be discovered, including dopamine (DA), norepinephrine (NE), epinephrine (E), and 5-hydroxytryptamine (5-HT), also known as serotonin. Amino acid neurotransmitters include: gamma-aminobutyric acid (GABA), glycine, glutamate, histamine, and acetylcholine (Ach). Peptide neurotransmitters are divided into: endogenous opioid peptides, substance P, vasopressin, cholecystokinin (CCK), somatostatin, vasopressin and oxytocin, and neuropeptide y. Other neurotransmitters are divided into: nucleotides, eicosanoids, anandamide, and sigma receptors (σ receptors). Other categories: Nitric oxide is generally considered to be a neurotransmitter. It is not released by exocytosis, but instead passes through the cell membrane due to its lipid solubility, exerts its effects and is inactivated through chemical reactions. It plays the role of retrograde messenger in synaptic plasticity changes and long-term potentiation effects.