Final answer:
The principal site for brain synthesis of norepinephrine is the locus coeruleus (LC), which is located in the brainstem.
Step-by-step explanation:
The principal site for brain synthesis of norepinephrine is the locus coeruleus (LC). The LC, located in the brainstem, contains the largest number of noradrenergic neurons in the brain and is responsible for the release of norepinephrine throughout the central nervous system (CNS). When the sympathetic nervous system is activated, these neurons release norepinephrine which can act both as a hormone and neurotransmitter. Norepinephrine synthesis is derived from the amino acid tyrosine and is chemically classified as a catecholamine, closely related to epinephrine (adrenaline).