Reuptake inhibitor

A reuptake inhibitor (RI) is a type of drug known as a reuptake modulator that inhibits the plasmalemmal transporter-mediated reuptake of a neurotransmitter from the synapse into the pre-synaptic neuron. This leads to an increase in extracellular concentrations of the neurotransmitter and an increase in neurotransmission. Various drugs exert their psychological and physiological effects through reuptake inhibition, including many antidepressants and psychostimulants. Most known reuptake inhibitors affect the monoamine neurotransmitters serotonin, norepinephrine (and epinephrine), and dopamine. However, there are also a number of pharmaceuticals and research chemicals that act as reuptake inhibitors for other neurotransmitters such as glutamate, γ-aminobutyric acid (GABA), glycine, adenosine, choline (the precursor of acetylcholine), and the endocannabinoids, among others. Standard reuptake inhibitors are believed to act simply as competitive substrates that work by binding directly to the plasmalemma transporter of the neurotransmitter in question. They occupy the transporter in place of the respective neurotransmitter and competitively block it from being transported from the nerve terminal or synapse into the pre-synaptic neuron. With high enough doses, occupation becomes as much as 80–90%. At this level of inhibition, the transporter will be considerably less efficient at removing excess neurotransmitter from the synapse and this causes a substantial increase in the extracellular concentrations of the neurotransmitter and therefore an increase in overall neurotransmission. Alternatively, some reuptake inhibitors bind to allosteric sites and inhibit reuptake indirectly and noncompetitively. Phencyclidine and related drugs such as benocyclidine, tenocyclidine, ketamine, and dizocilpine (MK-801), have been shown to inhibit the reuptake of the monoamine neurotransmitters. They appear to exert their reuptake inhibition by binding to vaguely characterized allosteric sites on each of the respective monoamine transporters.