Norepinephrine or noradrenaline (chemical formula C8H11NO3) is a catecholamine and phenethylamine chemical. It functions as a neurotransmitter as well as a hormone, and is secreted and released by the adrenal glands and by the noradrenergic neurons during synaptic transmission.
Outside the United States, norepinephrine is usually referred to as noradrenaline.
Norepinephrine is a stress hormone. The human brain releases it in times of stress, when the fight-or-flight response kicks in, in order to release energy from fat, increase heart rate, and increase muscle readiness. It also has an effect on the brain's attention and impulsivity.
The nucleus of the locus ceruleus in the brain stem is the origin of most of the brain's norepinephrine pathways; when stimulated, it triggers the physiological changes associated with a stressful event. Norepinephrine-stimulated neurons project from the locus ceruleus on paths to the cerebral cortex, limbic system, and the spinal cord.
Disorders and Norepinephrine
When norepinephrine and its pathways don't function properly in the brain, a host of disorders may occur, including depression and attention disorders. Both dopamine and norepinephrine may be transported along the same pathways, which often means that if norepinephrine paths are constricted it also affects dopamine paths. This problem can be treated with SNRIs and tricyclic antidepressants.
Attention and focus may also be affected by a lack of norepinephrine and/or dopamine. ADHD in both adults and children can be treated by norepinephrine reuptake inhibitors (all reuptake inhibitors increase the concentration of the substance they act upon in the brain). Antidepressants have also been used off-label to treat ADHD, and almost certainly work for the same reason they work for norepinephrine-related depression.
Norepinephrine by itself can be used in critically-ill patients as a vasopressor. Administered intravenously, it acts on alpha-1 and beta-1 adrenergic receptors to treat patients in septic shock, among other problems.
Web Resources On Norepinephrine
Regulation of extracellular dopamine by the norepinephrine transporter
Brain Norepinephrine Systems
Book Resources On Norepinephrine
Norepinephrine (Frontiers of Clinical Neuroscience, Vol 2) by Michael G. Ziegler
Control of release of norepinephrine from peripheral sympathetic nerves by Lydia H. Grobe