Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH2-CH2-). Examples are dopamine, norepinephrine and serotonin.
All monoamines are derived from aromatic amino acids like phenylalanine, tyrosine, and tryptophan by the action of aromatic amino acid decarboxylase enzymes. They are deactivated in the body by the enzymes known as monoamine oxidases which clip off the amine group.
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms (such as monoamine neurotransmission) because lipids can freely diffuse through membranes (see osmosis). One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum.
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The core body and brain temperatures increase during REM sleep and skin temperature decreases to lowest values.
The REM phase is also known as paradoxical sleep (PS) and sometimes desynchronized sleep or dreamy sleep, because of physiological similarities to waking states including rapid, low-voltage desynchronized brain waves. Electrical and chemical activity regulating this phase seem to originate in the brain stem, and is characterized most notably by an abundance of the neurotransmitter acetylcholine, combined with a nearly complete absence of monoamine neurotransmitters histamine, serotonin and norepinephrine. Experiences of REM sleep are not transferred to permanent memory due to absence of norepinephrine.
Monoamine oxidases (MAO) (EC 1.4.3.4) are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group. They are found bound to the outer membrane of mitochondria in most cell types of the body. The first such enzyme was discovered in 1928 by Mary Bernheim in the liver and was named tyramine oxidase. The MAOs belong to the protein family of flavin-containing amine oxidoreductases.
MAOs are important in the breakdown of monoamines ingested in food, and also serve to inactivate monoamine neurotransmitters. Because of the latter, they are involved in a number of psychiatric and neurological diseases, some of which can be treated with monoamine oxidase inhibitors (MAOIs) which block the action of MAOs.
Harmala alkaloids are several alkaloids that act as monoamine oxidase inhibitors (MAOIs). These alkaloids are found in the seeds of Peganum harmala (also known as harmal or Syrian rue), as well as Banisteriopsis caapi (ayahuasca), leaves of tobacco and coffee beans.
The alkaloids include harmine, harmaline, harmalol, and their derivatives, which have similar chemical structures, hence the name "harmala alkaloids". These alkaloids are of interest for their use in Amazonian shamanism, where they are derived from other plants. Harmine, once known as telepathine and banisterine, is a naturally occurring β-carboline alkaloid that is structurally related to harmaline, and also found in the vine Banisteriopsis caapi. Tetrahydroharmine is also found in B. caapi and P. harmala. Dr. Alexander Shulgin has suggested that harmine may be a breakdown product of harmaline. Harmine and harmaline are reversible inhibitors of monoamine oxidase A (RIMAs). They can stimulate the central nervous system by inhibiting the metabolism of monoamine compounds such as serotonin and norepinephrine.
A serotonin–norepinephrine–dopamine reuptake inhibitor (SNDRI), also known as a triple reuptake inhibitor (TRI or TUI), is a type of drug that acts as a combined reuptake inhibitor of the monoamine neurotransmitters serotonin, norepinephrine, and dopamine. Monoamine structures (including neurotransmitters) contain a singular amino group (mono) linked to an aromatic ring by a chain of two carbons. SNDRIs prevent reuptake of these monoamine neurotransmitters through the simultaneous inhibition of the serotonin transporter (SERT), norepinephrine transporter (NET), and dopamine transporter (DAT), respectively, increasing their extracellular concentrations and, therefore, resulting in an increase in serotonergic, adrenergic, and dopaminergic neurotransmission. SNDRIs were developed as potential antidepressants and treatments for other disorders, such as obesity, cocaine addiction, attention-deficit hyperactivity disorder (ADHD), and chronic pain. The increase in neurotransmitters through triple reuptake inhibition (including the addition of dopaminergic action) has the potential to heighten therapeutic effects in comparison to selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), reducing symptoms of depression and anxiety in people struggling with mental illness, as well as potentially combating other ailments such as those listed above.
However, increased side effects and abuse potential are concerns when using these agents relative to their SSRI and SNRI counterparts. Additionally, SNDRIs include the naturally occurring drug cocaine, a widely used recreational and often illegal drug for the euphoric effects it produces. Ketamine and phencyclidine are also SNDRIs and are similarly encountered as drugs of abuse. To a lesser extent, MDMA also acts as a SNDRI.