Monoamine transporters (MATs) are proteins that function as integral plasma-membrane transporters to regulate concentrations of extracellular monoamine neurotransmitters. The three major classes are serotonin transporters (SERTs), dopamine transporters (DATs), and norepinephrine transporters (NETs) and are responsible for the reuptake of their associated amine neurotransmitters. MATs are located just outside the synaptic cleft (peri-synaptically), transporting monoamine transmitter overflow from the synaptic cleft back to the cytoplasm of the pre-synaptic neuron. MAT regulation generally occurs through protein phosphorylation and post-translational modification. Due to their significance in neuronal signaling, MATs are commonly associated with drugs used to treat mental disorders as well as recreational drugs. Compounds targeting MATs range from medications such as the wide variety of tricyclic antidepressants, selective serotonin reuptake inhibitors such as fluoxetine (Prozac) to stimulant medications such as methylphenidate (Ritalin) and amphetamine in its many forms and derivatives methamphetamine (Desoxyn) and lisdexamfetamine (Vyvanse). Furthermore, drugs such as MDMA and natural alkaloids such as cocaine exert their effects in part by their interaction with MATs, by blocking the transporters from mopping up dopamine, serotonin, and other neurotransmitters from the synapse.
Serotonin–norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder (MDD), anxiety disorders, obsessive–compulsive disorder (OCD), social phobia, attention-deficit hyperactivity disorder (ADHD), chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. SNRIs are monoamine reuptake inhibitors; specifically, they inhibit the reuptake of serotonin and norepinephrine. These neurotransmitters are thought to play an important role in mood regulation. SNRIs can be contrasted with the selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which act upon single neurotransmitters.
Desipramine, sold under the brand name Norpramin among others, is a tricyclic antidepressant (TCA) used in the treatment of depression. It acts as a relatively selective norepinephrine reuptake inhibitor, though it does also have other activities such as weak serotonin reuptake inhibitory, α1-blocking, antihistamine, and anticholinergic effects. The drug is not considered a first-line treatment for depression since the introduction of selective serotonin reuptake inhibitor (SSRI) antidepressants, which have fewer side effects and are safer in overdose.
The 5-HT2A receptor is a subtype of the 5-HT2 receptor that belongs to the serotonin receptor family and is a G protein-coupled receptor (GPCR). The 5-HT2A receptor is a cell surface receptor, but has several intracellular locations.
Alaproclate is a drug that was being developed as an antidepressant by the Swedish pharmaceutical company Astra AB in the 1970s. It acts as a selective serotonin reuptake inhibitor (SSRI), and along with zimelidine and indalpine, was one of the first of its kind. Development was discontinued due to the observation of liver complications in rodent studies. In addition to its SSRI properties, alaproclate has been found to act as a non-competitive NMDA receptor antagonist, but does not have discriminative stimulus properties similar to phencyclidine.
A serotonin receptor agonist is an agonist of one or more serotonin receptors. They activate serotonin receptors in a manner similar to that of serotonin, a neurotransmitter and hormone and the endogenous ligand of the serotonin receptors.
Phenyltropanes (PTs) were originally developed to reduce cocaine addiction and dependency. In general these compounds act as inhibitors of the plasmalemmal monoamine reuptake transporters. This research has spanned beyond the last couple decades, and has picked up its pace in recent times, creating numerous phenyltropanes as research into cocaine analogues garners interest to treat addiction.
A serotonin–norepinephrine–dopamine reuptake inhibitor (SNDRI), also known as a triple reuptake inhibitor (TRI), is a type of drug that acts as a combined reuptake inhibitor of the monoamine neurotransmitters serotonin, norepinephrine, and dopamine. It does this by concomitantly inhibiting the serotonin transporter (SERT), norepinephrine transporter (NET), and dopamine transporter (DAT), respectively. Inhibition of the reuptake of these neurotransmitters increases their extracellular concentrations and, therefore, results in an increase in serotonergic, adrenergic, and dopaminergic neurotransmission. The naturally-occurring and potent SNDRI cocaine is widely used recreationally and often illegally for the euphoric effects it produces.
Indatraline hydrochloride is an antidepressive agent and non-selective monoamine transporter inhibitor that blocks the reuptake of dopamine, norepinephrine, and serotonin with similar efficacy to cocaine. This compound may be used to treat cocaine addictions as its effects have a slower onset and a longer duration than those of cocaine. Lu 19-005 has been shown to block the action of methamphetamine and MDMA in laboratory experiments.
Nisoxetine, originally synthesized in the Lilly research laboratories during the early 1970s, is a potent and selective inhibitor for the reuptake of norepinephrine (noradrenaline) into synapses. It currently has no clinical applications in humans, although it was originally researched as an antidepressant. Nisoxetine is now widely used in scientific research as a standard selective norepinephrine reuptake inhibitor. It has been used to research obesity and energy balance, and exerts some local analgesia effects.
Diclofensine (Ro 8-4650) was developed by Hoffmann-La Roche in the 1970s in the search for a new antidepressant. It was found that the (S)-isomer was responsible for activity. Diclofensine is a stimulant drug which acts as a triple monoamine reuptake inhibitor, primarily inhibiting the reuptake of dopamine and norepinephrine, with affinities (Ki) of 16.8 nM, 15.7 nM, and 51 nM for DAT, NET, and SERT (dopamine, norepinephrine and serotonin transporters), respectively. It was found to be an effective antidepressant in human trials, with relatively few side effects, but was ultimately dropped from clinical development, possibly due to concerns about its abuse potential.
Quipazine is a serotonergic drug of the piperazine group which is used in scientific research. It was originally intended as an antidepressant but never developed for medical use.
RTI(-4229)-336, is a phenyltropane derivative which acts as a potent and selective dopamine reuptake inhibitor and stimulant drug. It binds to the dopamine transporter with around 20x the affinity of cocaine, however it produces relatively mild stimulant effects, with a slow onset and long duration of action. These characteristics make it a potential candidate for treatment of cocaine addiction, as a possible substitute drug analogous to how methadone is used for treating heroin abuse. RTI-336 fully substitutes for cocaine in addicted monkeys and supports self-administration, and significantly reduces rates of cocaine use, especially when combined with SSRIs, and research is ongoing to determine whether it could be a viable substitute drug in human cocaine addicts.
Oxaprotiline, also known as hydroxymaprotiline, is a norepinephrine reuptake inhibitor belonging to the tetracyclic antidepressant (TeCA) family and is related to maprotiline. Though investigated as an antidepressant, it was never marketed.
MDAI (5,6-methylenedioxy-2-aminoindane) is a drug developed in the 1990s by a team led by David E. Nichols at Purdue University. It acts as a non-neurotoxic and highly selective serotonin releasing agent (SSRA) in vitro and produces entactogen effects in humans.
A dopamine releasing agent (DRA) is a type of drug which induces the release of dopamine in the body and/or brain. No selective DRAs are currently known. Many releasing agents of both dopamine and norepinephrine and of serotonin, norepinephrine, and dopamine are known, however. Serotonin–dopamine releasing agents are much rarer and are not selective for monoamine release. Examples of NDRAs include amphetamine and methamphetamine, and an example of an SNDRA is MDMA. The most selective dopamine releaser is 4-methylaminorex, but it also has considerable activity as a norepinephrine releaser. These drugs are frequently used for recreational purposes and encountered as drugs of abuse.
Litoxetine (developmental code names SL 81-0385, IXA-001) is an antidepressant which was under clinical development for the treatment of depression in the early 1990s but was never marketed. It acts as a potent serotonin reuptake inhibitor (Ki for SERTTooltip serotonin transporter = 7 nM) and modest 5-HT3 receptor antagonist (Ki = 315 nM). It has antiemetic activity, and unlike the selective serotonin reuptake inhibitors (SSRIs), appears to have a negligible incidence of nausea and vomiting. The drug is structurally related to indalpine. Development of litoxetine for depression was apparently ceased in the late 1990s. However, as of March 2017, development of litoxetine has been reinitiated and the drug is now in the phase II stage for the treatment of urinary incontinence.
Dextrallorphan (DXA) is a chemical of the morphinan class that is used in scientific research. It acts as a σ1 receptor agonist and NMDA receptor antagonist. It has no significant affinity for the σ2, μ-opioid, or δ-opioid receptor, or for the serotonin or norepinephrine transporter. As an NMDA receptor antagonist, in vivo, it is approximately twice as potent as dextromethorphan, and five-fold less potent than dextrorphan.
A monoamine reuptake inhibitor (MRI) is a drug that acts as a reuptake inhibitor of one or more of the three major monoamine neurotransmitters serotonin, norepinephrine, and dopamine by blocking the action of one or more of the respective monoamine transporters (MATs), which include the serotonin transporter (SERT), norepinephrine transporter (NET), and dopamine transporter (DAT). This in turn results in an increase in the synaptic concentrations of one or more of these neurotransmitters and therefore an increase in monoaminergic neurotransmission.
Selective serotonin reuptake inhibitors, or serotonin-specific re-uptake inhibitor (SSRIs), are a class of chemical compounds that have contributed to the major advances as antidepressants where they have revolutionised the treatment of depression and other psychiatric disorders. The SSRIs are therapeutically useful in the treatment of panic disorder (PD), posttraumatic stress disorder (PTSD), social anxiety disorder, obsessive-compulsive disorder (OCD), premenstrual dysphoric disorder (PMDD), and anorexia. There is also clinical evidence of SSRIs efficiency in the treatment of the negative symptoms of schizophrenia and their ability to prevent cardiovascular diseases.
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