Dopamine is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 80% of the catecholamine content in the brain. It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical, L-DOPA, which is synthesized in the brain and kidneys. Dopamine is also synthesized in plants and most animals. In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons to send signals to other nerve cells. Neurotransmitters are synthesized in specific regions of the brain, but affect many regions systemically. The brain includes several distinct dopamine pathways, one of which plays a major role in the motivational component of reward-motivated behavior. The anticipation of most types of rewards increases the level of dopamine in the brain, and many addictive drugs increase dopamine release or block its reuptake into neurons following release. Other brain dopamine pathways are involved in motor control and in controlling the release of various hormones. These pathways and cell groups form a dopamine system which is neuromodulatory.
Dopaminergic pathways in the human brain are involved in both physiological and behavioral processes including movement, cognition, executive functions, reward, motivation, and neuroendocrine control. Each pathway is a set of projection neurons, consisting of individual dopaminergic neurons.
The nigrostriatal pathway is a bilateral dopaminergic pathway in the brain that connects the substantia nigra pars compacta (SNc) in the midbrain with the dorsal striatum in the forebrain. It is one of the four major dopamine pathways in the brain, and is critical in the production of movement as part of a system called the basal ganglia motor loop. Dopaminergic neurons of this pathway release dopamine from axon terminals that synapse onto GABAergic medium spiny neurons (MSNs), also known as spiny projection neurons (SPNs), located in the striatum.
Dopaminergic means "related to dopamine", a common neurotransmitter. Dopaminergic substances or actions increase dopamine-related activity in the brain.
Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone, neurotransmitter and neuromodulator. The name "noradrenaline" is more commonly used in the United Kingdom, whereas "norepinephrine" is usually preferred in the United States. "Norepinephrine" is also the international nonproprietary name given to the drug. Regardless of which name is used for the substance itself, parts of the body that produce or are affected by it are referred to as noradrenergic.
Oxidopamine, also known as 6-hydroxydopamine (6-OHDA) or 2,4,5-trihydroxyphenethylamine, is a synthetic monoaminergic neurotoxin used by researchers to selectively destroy dopaminergic and noradrenergic neurons in the brain.
Levodopa, also known as L-DOPA and sold under many brand names, is a dopaminergic medication which is used in the treatment of Parkinson's disease and certain other conditions like dopamine-responsive dystonia and restless legs syndrome. The drug is usually used and formulated in combination with a peripherally selective aromatic L-amino acid decarboxylase (AAAD) inhibitor like carbidopa or benserazide. Levodopa is taken by mouth, by inhalation, through an intestinal tube, or by administration into fat.
5,7-Dihydroxytryptamine (5,7-DHT) is a monoaminergic neurotoxin used in scientific research to decrease concentrations of serotonin in the brain. The mechanism behind this effect is not well understood, but it is speculated to selectively destroy serotonergic neurons, in a manner similar to the dopaminergic neurotoxicity of 6-hydroxydopamine (6-OHDA). What is known is that this compound is in fact not selective in depleting serotonin content, but also depletes norepinephrine. To selectively deplete serotonin stores, it is commonly administered in conjunction with desmethylimipramine (desipramine), which inhibits the norepinephrine transporter.
A monoamine releasing agent (MRA), or simply monoamine releaser, is a drug that induces the release of a monoamine neurotransmitter from the presynaptic neuron into the synapse, leading to an increase in the extracellular concentrations of the neurotransmitter. Many drugs induce their effects in the body and/or brain via the release of monoamine neurotransmitters, e.g., trace amines, many substituted amphetamines, and related compounds.
d-Deprenyl, also known as or dextro-N-propargyl-N-methylamphetamine, is an MAO-B inhibitor that metabolizes into d-amphetamine and d-methamphetamine and is therefore also a norepinephrine–dopamine releasing agent. It is one of the two enantiomers of deprenyl and is the opposite enantiomer of l-deprenyl (selegiline).
Animal models of Parkinson's disease are essential in the research field and widely used to study Parkinson's disease. Parkinson's disease is a neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of the dopamine neurons in the brain, results in motor dysfunction, ultimately causing the four cardinal symptoms of PD: tremor, rigidity, postural instability, and bradykinesia. It is the second most prevalent neurodegenerative disease, following Alzheimer's disease. It is estimated that nearly one million people could be living with PD in the United States.
A monoamine neurotoxin, or monoaminergic neurotoxin, is a drug that selectively damages or destroys monoaminergic neurons. Monoaminergic neurons are neurons that signal via stimulation by monoamine neurotransmitters including serotonin, dopamine, and norepinephrine.
HPP+, also known as haloperidol pyridinium, is a monoaminergic neurotoxin and a metabolite of haloperidol.
5,6-Dihydroxytryptamine (5,6-DHT) is a monoaminergic neurotoxin and tryptamine derivative related to serotonin (5-hydroxytryptamine) and 5,7-dihydroxytryptamine (5,7-DHT). It is a relatively selective serotonergic neurotoxin, but also acts as a dopaminergic and noradrenergic neurotoxin at higher doses. In addition, it produces widespread generalized toxicity at higher doses. Its selective serotonergic neurotoxicity is due to its high affinity for the serotonin transporter (SERT). Because of its SERT affinity, 5,6-DHT has activity as a serotonin reuptake inhibitor.
Xylamine is a monoaminergic neurotoxin and benzylamine derivative that is closely related to DSP-4. It is a relatively selective noradrenergic neurotoxin, which is attributed to its high affinity for the norepinephrine transporter (NET). DSP-4 is generally preferred over xylamine for use in scientific research and hence xylamine is limitedly employed. Xylamine was first described in 1975.
ODMA is a bioisosteric analogue of 3,4-methylenedioxy-N-methylamphetamine (MDMA) which was developed in an attempt to create an improved MDMA alternative for potential clinical use. It is the analogue of MDMA in which the 1,3-benzodioxole ring has been replaced with a 2,1,3-benzoxadiazole ring. TDMA and SeDMA are closely related analogues. ODMA, TDMA, and SeDMA are releasing agents of serotonin, norepinephrine, and dopamine similarly to MDMA. However, they are less potent and efficacious in activating the serotonin 5-HT2A, 5-HT2B, and 5-HT2C receptors than MDMA and show differing and potentially improved metabolic and pharmacokinetic properties in comparison. ODMA, TDMA, and SeDMA were first described in the scientific literature in June 2024.
TDMA is a bioisosteric analogue of 3,4-methylenedioxy-N-methylamphetamine (MDMA) which was developed in an attempt to create an improved MDMA alternative for potential clinical use. It is the analogue of MDMA in which the 1,3-benzodioxole ring has been replaced with a 2,1,3-benzothiadiazole ring. ODMA and SeDMA are closely related analogues. ODMA, TDMA, and SeDMA are releasing agents of serotonin, norepinephrine, and dopamine similarly to MDMA. However, they are less potent and efficacious in activating the serotonin 5-HT2A, 5-HT2B, and 5-HT2C receptors than MDMA and show differing and potentially improved metabolic and pharmacokinetic properties in comparison. ODMA, TDMA, and SeDMA were first described in the scientific literature in June 2024.
SeDMA is a bioisosteric analogue of 3,4-methylenedioxy-N-methylamphetamine (MDMA) which was developed in an attempt to create an improved MDMA alternative for potential clinical use. It is the analogue of MDMA in which the 1,3-benzodioxole ring has been replaced with a 2,1,3-benzoselenadiazole ring. ODMA and TDMA are closely related analogues. ODMA, TDMA, and SeDMA are releasing agents of serotonin, norepinephrine, and dopamine similarly to MDMA. However, they are less potent and efficacious in activating the serotonin 5-HT2A, 5-HT2B, and 5-HT2C receptors than MDMA and show differing and potentially improved metabolic and pharmacokinetic properties in comparison. ODMA, TDMA, and SeDMA were first described in the scientific literature in June 2024.
2′-NH2-MPTP, also known as 2′-amino-MPTP, is a monoaminergic neurotoxin that was derived from MPTP and is used in scientific research to lesion brain monoaminergic systems in animals. Whereas MPTP is a selective dopaminergic neurotoxin, 2′-NH2-MPTP is a specific serotonergic and noradrenergic neurotoxin that doesn't affect dopaminergic neurons. 2′-NH2-MPTP is transported by the serotonin transporter (SERT) into serotonergic neurons and by the norepinephrine transporter (NET) into noradrenergic neurons, and its serotonergic and noradrenergic neurotoxicity is dependent on this transport by the SERT and NET, respectively. 2′-NH2-MPTP was first described in the scientific literature by 1993.
2′-CH3-MPTP, also known as 2′-methyl-MPTP, is a selective dopaminergic neurotoxin related to MPTP which is used in scientific research to lesion dopaminergic neurons. It is a considerably more potent dopaminergic neurotoxin than MPTP in mice but is less potent than MPTP in primates. MPTP and 2′-CH3-MPTP produce a Parkinson's disease-like condition in animals.
