Norepinephrine
Norepinephrine, known as noradrenaline outside the USA, is a catecholamine and a phenethylamine of the chemical formula C8H11NO3. It is released from the adrenal glands as a hormone into the blood, but it is also a neurotransmitter in the nervous system where it is released from noradrenergic neurons during synaptic transmission. It is one of the 'stress hormones' and affects parts of the human brain where attention and impulsivity are controlled. This compound affects the fight-or-flight response, activating the sympathetic nervous system to directly increase heart rate, release energy from fat and increase muscle readiness.
The host of physiological changes activated by a stressful event are unleashed in part by activation of a nucleus in the brain stem called the locus ceruleus. This nucleus is the origin of most norepinephrine pathways in the brain. Neurons using norepinephrine as their neurotransmitter project bilaterally from the locus ceruleus along distinct pathways to the cerebral cortex, limbic system, and the spinal cord, among other projections.
Synthesis
Norepinephrine is synthesized by a series of enzymatic step in the adrenal medulla from the amino acid tyrosine. The first reaction is the oxidation into Dihydroxyphenylalanine (L-DOPA), followed by decarboxylation into the neurotransmitter dopamine, and the final β-oxidation into norepinephrine. Norepinephrine can be further methylated to epinephrine (called adrenaline outside the USA).
