Neurotransmitters 1914 – Communication Between Nerves

Two years after receiving the Nobel Prize in 1936 for discovering the first neurotransmitter, German pharmacologist Otto Loewi was imprisoned by the Nazi regime because he was Jewish. Fortunately, he managed to escape the country using his Nobel Prize money.

In 1921, after dreaming about frog hearts, Loewi awoke and repeatedly stimulated the vagus nerve of a frog's heart, observing a reduction in its heart rate. He then collected fluid from around the heart and transferred it to a second frog heart without an attached vagus nerve. The fluid caused the second heart to beat more slowly. This suggested to Loewi that the vagus nerve released neurochemicals to control heart rate. These chemicals were later called acetylcholine and were first studied in 1914 by British physiologist Henry Dale. Loewi had correctly concluded that nerves could send "messages" by releasing neurotransmitter chemicals.

The synaptic cleft is the small gap separating two adjacent nerve cells. Consider these cells:

• Electrical activity in the presynaptic neuron causes it to release its stored neurotransmitter chemicals into small sacs (vesicles). 
• These chemicals diffuse towards receptors on the postsynaptic neuron. 
• Depending on the receptor type, a neurotransmitter may excite the postsynaptic neuron (making it more likely to send an action potential) or prevent the neuron from sending a signal. 
• The sum of these effects on the neuron determines whether the "message is transmitted".

Nitric oxide (a gas molecule) and beta-endorphin (a peptide neurotransmitter that binds to opioid receptors and may produce emotionally intense feelings) are among the many neurotransmitters discovered:

• Glutamate (a form of glutamic acid, an amino acid) usually excites postsynaptic neurons. 
• GABA (gamma-aminobutyric acid) is effective in stress control, and many sedatives or tranquillisers enhance its effects. 
• Acetylcholine transmits signals from motor neurons to muscles. 
• Dopamine levels play a role in Parkinson's disease and schizophrenia. Cocaine works by preventing dopamine reuptake (reabsorption) into the presynaptic neuron, leaving it in the cleft longer and increasing its effect. 
• Serotonin regulates sleep, memory and mood. Drugs such as Prozac inhibit serotonin reuptake, and LSD binds to most serotonin receptors.

Description of the article image: A neuron's electrical activity triggers the release of neurotransmitters stored in small sacs, shown in yellow-orange in the image. These chemicals diffuse across the gap to receptors on the postsynaptic neuron.

Historical figures mentioned in the article: Otto Loewi (1873–1961), Henry Hallett Dale (1875–1968)

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