Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex, touching on diverse functions including mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction.
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, social phobia, chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. Off-label uses include treatments for attention-deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD), and migraine prevention. 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.
A dopamine reuptake inhibitor (DRI) is a class of drug which acts as a reuptake inhibitor of the monoamine neurotransmitter dopamine by blocking the action of the dopamine transporter (DAT). Reuptake inhibition is achieved when extracellular dopamine not absorbed by the postsynaptic neuron is blocked from re-entering the presynaptic neuron. This results in increased extracellular concentrations of dopamine and increase in dopaminergic neurotransmission.
Noradrenergic and specific serotonergic antidepressants (NaSSAs) are a class of psychiatric drugs used primarily as antidepressants. They act by antagonizing the α2-adrenergic receptor and certain serotonin receptors such as 5-HT2A and 5-HT2C, but also 5-HT3, 5-HT6, and/or 5-HT7 in some cases. By blocking α2-adrenergic autoreceptors and heteroreceptors, NaSSAs enhance adrenergic and serotonergic neurotransmission in the brain involved in mood regulation, notably 5-HT1A-mediated transmission. In addition, due to their blockade of certain serotonin receptors, serotonergic neurotransmission is not facilitated in unwanted areas, which prevents the incidence of many side effects often associated with selective serotonin reuptake inhibitor (SSRI) antidepressants; hence, in part, the "specific serotonergic" label of NaSSAs.
Pindolol, sold under the brand name Visken among others, is a nonselective beta blocker which is used in the treatment of hypertension. It is also an antagonist of the serotonin 5-HT1A receptor, preferentially blocking inhibitory 5-HT1A autoreceptors, and has been researched as an add-on therapy to various antidepressants, such as clomipramine and the selective serotonin reuptake inhibitors (SSRIs), in the treatment of depression and obsessive-compulsive disorder.
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.
The serotonin 1A receptor is a subtype of serotonin receptors, or 5-HT receptors, that binds serotonin, also known as 5-HT, a neurotransmitter. 5-HT1A is expressed in the brain, spleen, and neonatal kidney. It is a G protein-coupled receptor (GPCR), coupled to the Gi protein, and its activation in the brain mediates hyperpolarization and reduction of firing rate of the postsynaptic neuron. In humans, the serotonin 1A receptor is encoded by the HTR1A gene.
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.
Reuptake inhibitors (RIs) are a type of reuptake modulators. It is a drug 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.
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.
A serotonin releasing agent (SRA) is a type of drug that induces the release of serotonin into the neuronal synaptic cleft. A selective serotonin releasing agent (SSRA) is an SRA with less significant or no efficacy in producing neurotransmitter efflux at other types of monoamine neurons.
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.
Tandamine is a selective norepinephrine reuptake inhibitor with a tricyclic structure. It was developed in the 1970s as an antidepressant but was never commercialized. Tandamine is analogous to pirandamine, which, instead, acts as a selective serotonin reuptake inhibitor (SSRI).
Desmethylsertraline (DMS), also known as norsertraline, is an active metabolite of the antidepressant drug sertraline. Like sertraline, desmethylsertraline acts as a monoamine reuptake inhibitor, and may be responsible for some of its parent's therapeutic benefits; however, the effects of DMS's main activity of increasing serotonin levels via binding to the serotonin transporter appears to be negligible as in vivo testing showed no measurable change in brain activity despite a nearly 20-fold increase in DMS blood levels compared to the EC50 (i.e. the amount required to achieve the desired effect in 50% of the population) of its parent drug sertraline. DMS is significantly less potent relative to sertraline as a serotonin reuptake inhibitor (Ki = 76 nM vs. 3 nM, respectively), but conversely, is more balanced as a monoamine reuptake inhibitor (5-HT (Ki) = 76 nM; NE (Ki) = 420 nM; DA (Ki) = 440 nM), which has the effective result of DMS contrarily behaving as a serotonin-norepinephrine-dopamine reuptake inhibitor (SNDRI), with about 5.5-fold preference for inhibiting serotonin reuptake relative to catecholamine reuptake.
Pirandamine (AY-23,713) is a tricyclic derivative which acts as a selective serotonin reuptake inhibitor (SSRI). It was investigated in the 1970s as a potential antidepressant but clinical development was not commenced and it was never marketed. Pirandamine is structurally related to tandamine, which, in contrast, is a selective norepinephrine reuptake inhibitor.
Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions.
Talsupram is a selective norepinephrine reuptake inhibitor (NRI) which was investigated as an antidepressant in the 1960s and 1970s but was never marketed. Along with talopram, it is structurally related to the selective serotonin reuptake inhibitor (SSRI) citalopram.
A serotonin–dopamine reuptake inhibitor (SDRI) is a type of drug which acts as a reuptake inhibitor of the monoamine neurotransmitters serotonin and dopamine by blocking the actions of the serotonin transporter (SERT) and dopamine transporter (DAT), respectively. This in turn leads to increased extracellular concentrations of serotonin and dopamine, and, therefore, an increase in serotonergic and dopaminergic neurotransmission.
Selective serotonin reuptake inhibitors, or serotonin-specific re-uptake inhibitor (SSRIs), are a class of chemical compounds that have application as antidepressants and in the treatment of depression and other psychiatric disorders. 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 the value of SSRIs in the treatment of the symptoms of schizophrenia and their ability to prevent cardiovascular diseases.
