Neurotransmitters and Neuroactive Peptides
Discovery of Neurotransmitters
In 1921, an Austrian scientist named Otto Loewi discovered the first neurotransmitter.
Otto Loewi's Experiment
Neurotransmitter Criteria
Neuroscientists have set up a few guidelines or criteria to prove that a chemical is really a neurotransmitter. Not all of the neurotransmitters that you have heard about may actually meet every one of these criteria.
Neurotransmitter Types
There are many types of chemicals that act as neurotransmitter substances. Below is a list of some of them.
Small Molecule Neurotransmitter Substances
Acetylcholine [ACh] | Dopamine [DA] | Norepinephrine [NE] |
Serotonin [5-HT] | Histamine | Epinephrine |
Amino Acids
Gamma-aminobutyric acid [GABA] | Glycine | Glutamate |
Aspartate |
Neuroactive Peptides - partial list only!
bradykinin | beta-endorphin | bombesin | calcitonin |
cholecystokinin | enkephalin | dynorphin | insulin |
gastrin | substance P | neurotensin | glucagon |
secretin | somatostatin | motilin | vasopressin |
oxytocin | prolactin | thyrotropin | angiotensin II |
sleep peptides | galanin | neuropeptide Y | thyrotropin-releasing hormone |
gonadotropnin-releasing hormone | growth hormone-releasing hormone | luteinizing hormone | vasoactive intestinal peptide |
Soluble Gases
Nitric Oxide [NO] | Carbon Monoxide |
Synthesis of Neurotransmitters
Acetylcholine is found in both the central and peripheral nervous systems. Choline is taken up by the neuron. When the enzyme called choline acetyltransferase is present, choline combines with acetyl coenzyme A [CoA] to produce acetylcholine.
Dopamine, norepinephrine and epinephrine are a group of neurotransmitters called "catecholamines". Norepinephrine is also called "noradrenalin" and epinephrine is also called "adrenalin". Each of these neurotransmitters is produced in a step-by-step fashion by a different enzyme.
Transport and Release of Neurotransmitters
Unlike other neurotransmitters, nitric oxide [NO] is not stored in synaptic vesicles. Rather, NO is released soon after it is produced and diffuses out of the neuron. NO then enters another cell where it activates enzymes for the production of "second messengers."
Receptor Binding
Neurotransmitters will bind only to specific receptors on the postsynaptic membrane that recognize them.
Inactivation of Neurotransmitters
The action of neurotransmitters can be stopped by four different mechanisms:
Try it! | Do you like interactive word search puzzles? Make sure your browser is "java-enabled" and try this Neurotransmitters Puzzle |
Did you know? | The idea for the famous heart experiment came to Otto Loewi in his sleep. In Loewi's own words: "In the night of Easter Saturday, 1921, I awoke, turned on the light, and jotted down a few notes on a tiny slip of paper. Then I fell asleep again. It occurred to me at six o'clock in the morning that during the night I had written down something most important, but I was unable to decipher the scrawl. That Sunday was the most desperate day in my whole scientific life. During the next night, however, I awoke again, at three o'clock, and I remembered what it was. This time I did not take any risk; I got up immediately, went to the laboratory, made the experiment on the frog's heart, described above, and at five o' clock the chemical transmission of nervous impulse was conclusively proved." --- quoted from Loewi, O., From the Workshop of Discoveries, Lawrence: University of Kansas Press, 1953. |
Copyright © 1996-2020, Eric H. Chudler All Rights Reserved.