Neurotransmitters are chemical messengers that transmit a signal from a neuron across the synapse to a target cell, which can be a different neuron, muscle cell, or gland cell. Neurotransmitters are chemical substances made by the neuron specifically to transmit a message.
Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by neurotransmitter receptors on the target cell.
Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available and only require a small number of biosynthetic steps for conversion. Neurotransmitters are essential to the function of complex neural systems. The exact number of unique neurotransmitters in humans is unknown, but more than 500 have been identified.
There are four main criteria for identifying neurotransmitters:
- The chemical must be synthesized in the neuron or otherwise be present in it.
- When the neuron is active, the chemical must be released and produce a response in some targets.
- The same response must be obtained when the chemical is experimentally placed on the target.
- A mechanism must exist for removing the chemical from its site of activation after its work is done.
• Amino acids: glutamate, aspartate, D-serine, glycine
• Gasotransmitters: nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S)
• Monoamines: dopamine (DA), norepinephrine (noradrenaline; NE, NA), epinephrine (adrenaline), histamine, serotonin (SER, 5-HT)
• Catecholamines: dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline)
• Trace amines: phenethylamine, N-methylphenethylamine, tyramine, 3-iodothyronamine, octopamine, tryptamine, etc.
• Peptides: oxytocin, somatostatin, substance P, cocaine and amphetamine regulated transcript, opioid peptides
• Purines: adenosine triphosphate (ATP), adenosine
• Others: acetylcholine (ACh), anandamide, etc.
In addition, over 50 neuroactive peptides have been found, and new ones are discovered regularly.
Understanding the effects of drugs on neurotransmitters comprises a significant portion of research initiatives in the field of neuroscience. Most neuroscientists involved in this field of research believe that such efforts may further advance our understanding of the circuits responsible for various neurological diseases and disorders, as well as ways to effectively treat and someday possibly prevent or cure such illnesses.
Drugs can influence behavior by altering neurotransmitter activity.
A neurotransmitter must be broken down once it reaches the post-synaptic cell to prevent further excitatory or inhibitory signal transduction. This allows new signals to be produced from the adjacent nerve cells.