Norepinephrine neurons (NE) in the brain
The source nuclei for the norepinephrine neurons are located in the locus coeruleus in the brain stem. These neurons project throughout the brain (cortex, hippocampus, thalamus and midbrain) and spinal cord.
Noradrenaline has excitatory activity within the brain, and its pathways are thought to be involved in the control of functions such as attention and arousal.
Outside the brain, noradrenaline is the main neurotransmitter of the sympathetic nervous system. Systemically, therefore, changes in noradrenergic activity induce changes in e.g. heart rate, blood pressure and gastrointestinal activity. This explains the broad side-effect profile associated with drugs that affect monoamine neurotransmitters, such as the tricyclic antidepressants.