AP5 or APV is a selective NMDA receptor antagonist

NMDA receptor antagonist

NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the N-methyl d-aspartate receptor . They are used as anesthesia for animals and, less commonly, for humans; the state of anesthesia they induce is referred to as dissociative anesthesia...

 that competitively inhibits

Competitive inhibition

Competitive inhibition is a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa.-Mechanism:...

 the ligand (glutamate) binding site of NMDA receptor

NMDA receptor

The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....

s.

AP5 blocks the cellular analog of classical conditioning

Classical conditioning

Classical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...

 in the sea slug Aplysia californica, and has similar effects on Aplysia long-term potentiation

Long-term potentiation

In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...

, since NMDA receptors are required for both. It is sometimes used in conjunction with the calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 chelator BAPTA

BAPTA

BAPTA is a calcium-specific polyamino carboxylic acid. The presence of four carboxylic acid functional groups makes possible the binding of two magnesium ions. The extensive flexibility of the carboxylate ligands is critical to the coordination of magnesium, or other metal ions...

 to determine whether NMDARs are required for a particular cellular process.

In general, AP5 is very fast-acting within in vitro

In vitro

In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

 preparations, and can block NMDA receptor action at a reasonably small concentration. The active isomer

Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

 of AP5 is considered to be the D configuration, although many preparations are available as a racemic

Racemic

In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...

 mixture of D- and L-isomers. It is useful to isolate the action of other glutamate receptors in the brain, i.e., AMPA

AMPA receptor

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor is a non-NMDA-type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system . Its name is derived from its ability to be activated by the artificial glutamate analog AMPA...

 and kainate receptor

Kainate receptor

Kainate receptors, or KARs, are non-NMDA ionotropic receptors which respond to the neurotransmitter glutamate. They were first identified as a distinct receptor type through their selective activation by the agonist kainate, a drug first isolated from red algae Digenea simplex. KARs are less well...

s.

AP5 can block the conversion of a silent synapse

Silent synapse

In neuroscience, a silent synapse is an excitatory glutamatergic synapse whose postsynaptic membrane contains NMDA-type glutamate receptors but no AMPA-type glutamate receptors. These synapses are named "silent" because normal AMPA receptor-mediated signaling is not present, rendering the synapse...

 to an active one, since this conversion is NMDA receptor-dependent.

AP5 was developed by Jeff Watkins and Harry Olverman.