Figure 2.

The role of norepinephrine at synapses. Norepinephrine is synthesized in a multistep process. Tyrosine is converted to L-DOPA via the activity of tyrosine hydroxylase (TH). L-DOPA is then decarboxylated via DOPA decarboxylase into dopamine. Dopamine via dopamine beta-hydroxylase (DBH) is then converted to norepinephrine (NE). NE is released at synapses where it can bind to α- adrenergic receptors or β- adrenergic receptors on postsynaptic neurons to modulate neuronal firing or modulate adrenergic neurons signaling. NE excess can be eliminated via the activity of monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT). NE can also be recycled back to presynaptic neurons via the NE transporters (NET).