Norepinephrine binds to metabotropic adrenergic receptors (α1, α2, and β). Norepinephrine is synthesized from dopamine by dopamine beta-hydroxylase after packaging into vesicles. Once inside the cell, dopamine is either degraded via the actions of either monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT), or it is repackaged into vesicles. Dopamine binds to metabotropic receptors on postsynaptic cells. Instead, there are generally only a few patches of neurons that produce dopamine, most of which are found in the midbrain. Unlike glutamate or GABA, dopamine-producing neurons are not widely abundant in the brain. Swedish physiologist Ulf von Euler identified norepinephrine in the mid-1940s; he received a share of the 1970 Nobel Prize for Physiology or Medicine for his discovery. People with depression may be treated with a class of medications called serotonin and norepinephrine reuptake inhibitors (SNRIs). ADHD medications target norepinephrine and dopamine, both of which affect your attention and concentration, according to KidsHealth. Epinephrine, also known as adrenaline, plays an important role in your body’s fight-or-flight response. As a hormone, epinephrine is made from norepinephrine inside of your adrenal gland. Epinephrine is part of your sympathetic nervous system, which is part of your body’s emergency response system to danger — the "fight-or-flight" response. Epinephrine, also called adrenaline, is both a hormone and a neurotransmitter. This reaction causes a number of changes in your body and is known as the fight-or-flight response. As a neurotransmitter, it’s a chemical messenger that helps transmit nerve signals across nerve endings to another nerve cell, muscle cell or gland cell. It plays an important role in your body’s "fight-or-flight" response. An injection of epinephrine can help open up your airway so you can breathe. As hormones, they influence different parts of your body and stimulate your central nervous system. Norepinephrine is transported back into the cytosol of the presynaptic neuron (uptake 1) or a nearby non-neuronal cell (uptake 2). Norepinephrine-mediated signal transduction and ultimate cellular function depend on which type of receptor (α-adrenergic or β-adrenergic receptor) it binds. Noradrenergic neurons are projected bilaterally from this nucleus to several brain areas, including the cerebral cortex, limbic system, and spinal cord. Vesicular monoamine transporter (VMAT) protein is responsible for transporting norepinephrine into synaptic vesicles. After synthesis, norepinephrine is stored in the synaptic vesicles. Both of these catecholamines bind to adrenergic receptors and participate in the fight-or-flight response. Structurally, norepinephrine is quite similar to epinephrine, another catecholamine, except that a methyl group in epinephrine is replaced by a hydrogen atom in norepinephrine. Norepinephrine has been reported to exist in a wide variety of animal species, including protozoa, placozoa and cnidaria (jellyfish and related species), but not in ctenophores (comb jellies), whose nervous systems differ greatly from those of other animals. There is also substantial evidence that many people with ADHD show biomarkers involving altered norepinephrine processing. If sympathetic activity is elevated for an extended time, it can cause weight loss and other stress-related body changes. Hyperactivation of the sympathetic nervous system is not a recognized condition in itself, but it is a component of a number of conditions, as well as a possible consequence of taking sympathomimetic drugs. The main hemodynamic function of norepinephrine is to increase systolic, diastolic, and pulse pressures. After uptake, norepinephrine is rapidly degraded to various metabolites, including normetanephrine, dihydroxymandelic acid, vanilmandelate, and epinephrine. After execution of the work, the signal is terminated by cellular uptake and degradation of norepinephrine. In the brainstem, the locus coeruleus is the primary site of norepinephrine synthesis. Lastly, dopamine is converted into norepinephrine by dopamine beta hydroxylase. Norepinephrine is synthesized from the amino acid tyrosine in the adrenal medulla and postganglionic neurons of the sympathetic nervous system. Norepinephrine is a strong vasoconstrictor frequently used to treat severe hypotension by increasing systemic vascular resistance and blood pressure. Stressors of many types evoke increases in noradrenergic activity, which mobilizes the brain and body to meet the threat. Monoamine oxidase A inhibitors (MAO-A) are antidepressants that inhibit the metabolic degradation of norepinephrine as well as serotonin and dopamine. Drugs belonging to this group can have very different effects, however, depending on whether they primarily block alpha-1 receptors, alpha-2 receptors, or both. It has been argued that this similarity arises because both are to a large degree controlled by the same brain structures, particularly a part of the brainstem called the nucleus gigantocellularis. The noradrenergic neurons in the brain form a neurotransmitter system, that, when activated, exerts effects on large areas of the brain. It is found that the endocannabinoid anandamide and the cannabinoid WIN 55,212-2 can modify the overall response to sympathetic nerve stimulation, which indicates that prejunctional CB1 receptors mediate the sympatho-inhibitory action. Norepinephrine is the main neurotransmitter used by the sympathetic nervous system, which consists of about two dozen sympathetic chain ganglia located next to the spinal cord, plus a set of prevertebral ganglia located in the chest and abdomen. Catecholamines are a class of neurotransmitters that are found within the larger class of neurotransmitters, biogenic amines. Norepinephrine activity is efficiently terminated through inactivation by the enzymes catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO), by reuptake into nerve endings, or by diffusion from binding sites. The substance has also been shown to modulate the function of certain types of immune cells (e.g., T cells). Its major site of storage and release are the neurons of the sympathetic nervous system (a branch of the autonomic nervous system). Norepinephrine is classified structurally as a catecholamine—it contains a catechol group (a benzene ring with two hydroxyl groups) bound to an amine (nitrogen-containing) group. The consequences can include slowing of growth (in children), sleeplessness, loss of libido, gastrointestinal problems, impaired disease resistance, slower rates of injury healing, depression, and increased vulnerability to addiction. Stress, to a physiologist, means any situation that threatens the continued stability of the body and its functions.
