40 Fun Facts About Neurotransmitters

Neurotransmitters are released by one neuron and picked up by receptors on the next: what exactly are they?

Chemical messengers are how neurons signal across the tiny gap between them. Scientists know of at least 100 neurotransmitters and suspect many others are yet to be discovered.

Death of dopamine-producing neurons in the brain's substantia nigra causes which movement disorder?

Parkinson's disease is spotted late in the damage: by the time movement symptoms appear, 50–80% of the dopamine neurons in the substantia nigra have already degenerated.

Wrinkle-smoothing injections block acetylcholine release using a diluted form of the toxin behind which illness?

Botulism is the paralysing illness caused by botulinum toxin, the active ingredient of Botox. By stopping nerve endings releasing acetylcholine, it relaxes the muscles under facial wrinkles.

Serotonin is famous as a mood transmitter, but about 90% of the body's supply is made where?

The gut makes most of it: enterochromaffin cells in the gastrointestinal tract produce serotonin, which regulates intestinal movements.

Caffeine keeps people alert by blocking the brain's receptors for which sleepiness-promoting molecule?

Adenosine builds up in the brain during waking hours, creating the need to sleep. Caffeine has a similar three-dimensional structure, so it binds to the same receptors and blocks them.

Which hormone triggers contractions during labour and also acts in the brain to strengthen social bonding?

Oxytocin is made in the hypothalamus and released by the posterior pituitary. Its role in bonding has earned it the nicknames 'cuddle hormone' and 'love hormone'.

Which amino acid, wrongly blamed for drowsiness after a turkey dinner, is the body's raw material for serotonin?

Tryptophan is no more plentiful in turkey than in other meats. The after-dinner slump may come instead from the other foods on the plate, particularly carbohydrates.

What does the brain release during hard exercise that blocks pain like the body's own morphine?

Endorphins take their name from a contraction of 'endogenous morphine', meaning morphine made within the body. They block the perception of pain and increase feelings of well-being.

Fluoxetine, which treats depression by blocking the reuptake of serotonin, became famous under which brand name?

Prozac was the name Eli Lilly gave the drug, which it began marketing in the US a month after approval in December 1987. Annual US sales reached $350 million within a year.

Which mind-altering drug, first made by Swiss chemist Albert Hofmann, works mainly through serotonin receptors?

LSD is a semisynthetic drug derived from ergot. Hofmann first made it in 1938 but discovered its potent psychedelic effects only in 1943, after accidentally ingesting some.

Which drug is best known for jamming the transporter that clears dopamine from the synapse?

Cocaine binds tightly to the dopamine transporter and blocks its function, so dopamine lingers in the synapse. The drug comes from the leaves of two coca species native to South America.

Valium and Xanax calm anxiety by enhancing the effect of GABA: to which drug class do they belong?

Benzodiazepines began with an accident: Leo Sternbach discovered the first, Librium, by chance in 1955. Valium followed in 1963.

Methylphenidate, a stimulant that blocks dopamine reuptake, is prescribed for ADHD under which brand name?

Ritalin was the original Novartis brand for the drug. Because the extra dopamine acts on the brain's reward system, the drug can also induce euphoria.

Haloperidol and chlorpromazine, drugs that block dopamine D2 receptors, are used mainly to treat which condition?

Schizophrenia is the principal use of antipsychotics, a drug class first introduced in the 1950s. Most of them work in much the same way: by blocking D2 dopamine receptors.

Loss of the brain cells that release orexin, a wakefulness-promoting peptide, causes which sleep disorder?

Narcolepsy type 1 follows the loss of the orexin-releasing neurons in the lateral hypothalamus. It can bring cataplexy: a sudden loss of muscle tone triggered by strong emotion.

Donepezil, sold as Aricept, slows the breakdown of acetylcholine to ease the symptoms of which condition?

Alzheimer's disease is treated with donepezil because the drug blocks acetylcholinesterase, the enzyme that breaks acetylcholine down. There is no evidence that it alters the course of the illness.

Which drug, carried as the nasal spray Narcan, reverses overdoses by blocking the brain's opioid receptors?

Naloxone given as a nasal spray takes effect in about ten minutes and is commonly used to restore breathing after an opioid overdose. Its block lasts only 30 to 90 minutes.

Which branched extensions of a neuron, studded with receptors, receive signals from other nerve cells?

Dendrites take their name from the Greek word for 'tree'. Those of a single large pyramidal cell receive signals from about 30,000 other neurons.

Unlike neurotransmitters crossing a synapse, hormones reach distant organs by which route?

The bloodstream carries hormones from the glands that secrete them to distant organs and tissues. A neurotransmitter, by contrast, often acts over distances measured in micrometres.

Which drug 'awakened' survivors of the 1920s encephalitis lethargica epidemic in Oliver Sacks's book Awakenings?

L-DOPA is the precursor the body turns into dopamine. Sacks found its effects on his patients' symptoms generally dramatic but temporary.

Neurotransmitters wait at the axon terminal packed inside which tiny sacs, the subject of a 2013 Nobel Prize?

Vesicles empty their cargo by fusing with the nerve cell's membrane. Thomas Südhof, James Rothman and Randy Schekman won the 2013 Nobel Prize for their work on how they are trafficked.

When a nerve impulse reaches the axon terminal, an inrush of which ion triggers the release of neurotransmitter?

Calcium ions flow in through voltage-dependent channels and bind to synaptotagmin proteins, which lets the stored packets of transmitter fuse with the membrane and spill into the synapse.

Which brief electrical signal travels down a neuron's axon and triggers neurotransmitter release at the far end?

An action potential is an all-or-none signal: it either occurs fully or does not occur at all. The sodium-based kind is over in about a millisecond.

GABA, the transmitter whose work is enhanced by Valium, has which kind of effect on most mature neurons?

Inhibitory transmitters reduce a neuron's excitability. GABA, the principal one in the mature brain, works through receptors whose channels carry chloride ions across the cell membrane.

Morphine switches on opioid receptors rather than blocking them: what is a drug that acts this way called?

An agonist binds to a receptor and activates it, much as the body's own transmitter would. An antagonist does the reverse and blocks the receptor instead.

Which amino acid, the nervous system's most abundant excitatory transmitter, is also the raw material for GABA?

Glutamate is the transmitter of nearly all the excitatory neurons in the central nervous system. A single enzyme, glutamate decarboxylase, converts it into GABA.

The locus coeruleus, a 'blue spot' in the brainstem, is the brain's principal source of which alertness transmitter?

Norepinephrine release is lowest during sleep, rises during wakefulness and reaches much higher levels in situations of stress or danger: the fight-or-flight response.

Older allergy tablets cause drowsiness by blocking brain receptors for which wake-promoting transmitter?

Histamine neurons in the hypothalamus fire rapidly during wakefulness and stop firing altogether during sleep. Newer allergy drugs cross into the brain far less, so they sedate less.

Which gas, whose signalling role in the body won a 1998 Nobel Prize, also works as a neurotransmitter?

Nitric oxide is highly reactive, with a lifetime of a few seconds, yet it diffuses freely across cell membranes, so it has no need of a receptor on the cell surface.

Which pharmacologist proved that nerves release a transmitter by passing fluid between two frog hearts?

Otto Loewi said the experiment came to him in a dream. He named the heart-slowing substance 'Vagusstoff', and it was later found to be acetylcholine.

Which nerve agent, released on the Tokyo subway by a cult in 1995, blocks the enzyme that clears acetylcholine?

Sarin stops acetylcholinesterase from degrading acetylcholine, so muscles cannot relax. Inhaling a lethal dose can kill within one to ten minutes through respiratory paralysis.

Which arrow poison, used by South American hunters, paralyses prey by blocking acetylcholine receptors on muscle?

Curare kills by asphyxiation, because the breathing muscles can no longer contract. It is harmless when taken by mouth and becomes active only when it gets into a wound.

In which autoimmune disease do antibodies attack the acetylcholine receptors where nerve meets muscle?

Myasthenia gravis takes its name from Greek and Latin words for serious muscle weakness. In about two-thirds of people, the first symptom involves the muscles around the eye.

Which drug from deadly nightshade blocks acetylcholine receptors, widening the pupils and speeding the heart?

Atropine was named in the 19th century, when pure extracts were first made from the belladonna plant, Atropa belladonna. Eye doctors still use it to dilate the pupils.

The venom of which spider works by forcing nerve endings to dump acetylcholine and other neurotransmitters?

Black widow venom owes its effects to latrotoxins. The best studied, α-latrotoxin, makes sensory and motor neurons release their transmitters in bursts.

Strychnine causes violent convulsions by blocking the spinal cord's receptors for which calming transmitter?

Glycine is the simplest stable amino acid as well as a transmitter in the spinal cord and brainstem. With its braking signal blocked, strychnine poisoning ends in death through asphyxia.

Which brain transmitter, named after the Sanskrit word for bliss, binds the same receptors as the THC in cannabis?

Anandamide was first reported in 1992 and was the first marijuana-like substance found in mammals. Its name joins the Sanskrit word ananda to 'amide'.

Which physiologist coined the word 'synapse' for the junction between nerve cells and later won a Nobel Prize?

Charles Sherrington introduced the term in 1897 and shared the 1932 Nobel Prize with Edgar Adrian. Three of his students, among them Howard Florey, went on to become Nobel laureates themselves.

Which scientist shared the 2000 Nobel Prize for showing that dopamine is a neurotransmitter in its own right?

Arvid Carlsson showed that animals given the drug reserpine lost dopamine and, with it, control of their movements. He also found dopamine levels were particularly high in the basal ganglia.

Which enzyme, blocked by some of the earliest antidepressants, breaks down serotonin and dopamine?

Monoamine oxidase came to notice by luck: iproniazid, a drug developed for tuberculosis, turned out to block the enzyme and to work as an antidepressant.