Norepinephrine, which is also known as noradrenaline, is a monoamine neurotransmitter that also functions as a hormone in the brain and body.
The name “noradrenaline,” is derived by the United Kingdom from the Latin roots meaning “at/alongside the kidneys,”.
In the United States, “norepinephrine,” is derived from Greek roots having that same meaning.
The parts of the body that produce or are affected by it are referred to as noradrenergic.
Norepinephrine’s function in the brain
In the brain, norepinephrine is produced in closely packed brain cell neurons or nuclei that are small yet exert powerful effects on other brain areas.
The most important of these nuclei is the locus coeruleus, located in the pons. Outside the brain, norepinephrine is used as a neurotransmitter by sympathetic ganglia located near the spinal cord or in the abdomen, and it is also released directly into the bloodstream by the adrenal glands. Regardless of how and where it is released, norepinephrine acts on target cells by binding to and activating noradrenergic receptors located on the cell surface.
The general function of norepinephrine is to mobilize the brain and body for action. Norepinephrine release is lowest during sleep, rises during wakefulness, and reaches much higher levels during situations of stress or danger, in the so-called fight-or-flight response. In the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, and focuses attention; it also increases restlessness and anxiety. In the rest of the body, norepinephrine increases heart rate and blood pressure, triggers the release of glucose from energy stores, increases blood flow to skeletal muscle, reduces blood flow to the gastrointestinal system, and inhibits voiding of the bladder and gastrointestinal motility.
A variety of medically important drugs work by altering the actions of norepinephrine systems. Norepinephrine itself is widely used as an injectable drug for the treatment of critically low blood pressure. Beta blockers, which counter some of the effects of norepinephrine, are frequently used to treat glaucoma, migraine, and a range of cardiovascular problems. Alpha blockers, which counter a different set of norepinephrine effects, are used to treat several cardiovascular and psychiatric conditions. Alpha-2 agonists often have a sedating effect, and are commonly used as anesthesia-enhancers in surgery, as well as in treatment of drug or alcohol dependence. Many important psychiatric drugs exert strong effects on norepinephrine systems in the brain, resulting in side-effects that may be helpful or harmful.
Noradrenaline (also called norephinephrine) acts on the adrenergic (or sympathetic) nervous system and is involved in mediating cardiovascular effects, arousal, concentration, attention, learning and memory (Ressler & Nemeroff, 1999). Noradrenaline acts on adrenergic receptors in the Central Nervous System (CNS) and the periphery. There are two types of adrenergic receptors (a and b) and for each type there are a number of subtypes (Lynch, Harrison & Pearson, 1994; Michelotti, Price & Schwinn, 2000).