''N''-methyl--aspartic acid or ''N''-methyl--aspartate (NMDA) is an

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

derivative that acts as a specific

agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ag ...

at the

NMDA receptor The ''N''-methyl-D-aspartate receptor (also known as the NMDA receptor or NMDAR), is a glutamate receptor and ion channel found in neurons. The NMDA receptor is one of three types of ionotropic glutamate receptors, the other two being AMPA and ...

mimicking the action of

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...

, the

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neu ...

which normally acts at that receptor. Unlike glutamate, NMDA only binds to and regulates the NMDA receptor and has no effect on other glutamate receptors (such as those for

AMPA α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, better known as AMPA, is a compound that is a specific agonist for the AMPA receptor, where it mimics the effects of the neurotransmitter glutamate. There are several types of glutamatergic ...

and kainate). NMDA receptors are particularly important when they become overactive during, for example, withdrawal from

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

as this causes symptoms such as agitation and, sometimes, epileptiform

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with lo ...

Biological function

In 1962, J.C. Watkins reported synthesizing NMDA, an

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...

of the previously know
''N''-Methyl--aspartic-acid (PubChem ID 4376)
NMDA is a water-soluble -alpha-amino acid — an

aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...

derivative with an ''N''-methyl substituent and -

configuration Configuration or configurations may refer to: Computing * Computer configuration or system configuration * Configuration file, a software file used to configure the initial settings for a computer program * Configurator, also known as choice bo ...

— found across

Animalia Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

from

lancelet The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochord ...

s to

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s. At homeostatic levels NMDA plays an essential role as a neurotransmitter and neuroendocrine regulator. At increased but sub–toxic levels NMDA becomes neuro-protective. In excessive amounts NMDA is an excitotoxin. Behavioral neuroscience research utilizes NMDA

excitotoxicity In excitotoxicity, nerve cells suffer damage or death when the levels of otherwise necessary and safe neurotransmitters such as glutamate become pathologically high, resulting in excessive stimulation of receptors. For example, when glutamate ...

to induce lesions in specific regions of an

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

subject's brain or spinal cord to study behavioral changes. The mechanism of action for the

is a specific agonist binding to its NR2 subunits, and then a non-specific cation channel is opened, which can allow the passage of Ca²⁺ and Na⁺ into the cell and K⁺ out of the cell. Therefore, NMDA receptors will only open if glutamate is in the synapse and concurrently the postsynaptic membrane is already depolarized - acting as coincidence detectors at the neuronal level. The

excitatory postsynaptic potential In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the ...

(EPSP) produced by activation of an NMDA receptor also increases the concentration of Ca²⁺ in the cell. The Ca²⁺ can in turn function as a second messenger in various signaling pathways. This process is modulated by a number of endogenous and exogenous compounds and plays a key role in a wide range of physiological (such as memory) and pathological processes (such as

Antagonists

Examples of antagonists, or more appropriately named receptor channel blockers, of the NMDA receptor are APV,

amantadine Amantadine, sold under the brand name Gocovri among others, is a medication used to treat dyskinesia associated with parkinsonism and influenza caused by type A influenzavirus, though its use for the latter is no longer recommended due to wid ...

dextromethorphan Dextromethorphan (DXM) is a medication most often used as a cough suppressant in over-the-counter cold and cough medicines. It is sold in syrup, tablet, spray, and lozenge forms. In 2022, the FDA approved a formulation of it combined with b ...

(DXM),

ketamine Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppress ...

, magnesium, tiletamine,

phencyclidine Phencyclidine or phenylcyclohexyl piperidine (PCP), also known as angel dust among other names, is a dissociative anesthetic mainly used recreationally for its significant mind-altering effects. PCP may cause hallucinations, distorted percept ...

(PCP),

riluzole Riluzole is a medication used to treat amyotrophic lateral sclerosis and other motor neuron diseases. Riluzole delays the onset of ventilator-dependence or tracheostomy in some people and may increase survival by two to three months. Riluzole i ...

memantine Memantine is a medication used to slow the progression of moderate-to-severe Alzheimer's disease. It is taken by mouth. Common side effects include headache, constipation, sleepiness, and dizziness. Severe side effects may include blood clots ...

, methoxetamine (MXE),

methoxphenidine Methoxphenidine (methoxydiphenidine, 2-MeO-Diphenidine, MXP) is a dissociative of the diarylethylamine class that has been sold online as a designer drug. Methoxphenidine was first reported in a 1989 patent where it was tested as a treatment for ...

(MXP) and kynurenic acid. While

dizocilpine Dizocilpine ( INN), also known as MK-801, is a pore blocker of the ''N''-Methyl-D-aspartate (NMDA) receptor, a glutamate receptor, discovered by a team at Merck in 1982. Glutamate is the brain's primary excitatory neurotransmitter. The channel is ...

is generally considered to be the prototypical NMDA receptor blocker and is the most common agent used in research, animal studies have demonstrated some amount of

neurotoxicity Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specificall ...

, which may or may not also occur in humans. These compounds are commonly referred to as

NMDA receptor antagonist NMDA receptor antagonists are a class of drugs that work to antagonize, or inhibit the action of, the ''N''-Methyl-D-aspartate receptor ( NMDAR). They are commonly used as anesthetics for animals and humans; the state of anesthesia they induce ...

Biological function

Antagonists

See also

References

Further reading