Noradrenergic nerve terminal Norepinephrine production adrenergic neurons transport tyrosine by a transport protein to synthesize norepinephrine adrenergic and dopaminergic neurons use the same pathway adrenergic neurons modify NE to Epi dopaminergic neurons terminates at dopamine tyrosine → dopa → dopamine → norepinephrine → epinephrine the rate limiting step is the conversion of tyrosine to dopa by tyrosine hydroxylase can be inhibited by metyrosine NE pathway feedback NE: negative feedback by acting on presynaptic α2 autoreceptors to inhibit further NE release ACh: acts on M2 receptors also to inhibit further NE release angiotensin II: activates NE release Pathway Inhibitors reserpine: inhibits the vesicular monoamine transporter (VMAT) preventing the storage of neurotransmitters guanethidine: replaces the NE inside the neurotransmitter vesicles and depletes the vesicle of NE cocaine and tricyclic antidepressants: inhibits the NET (reuptake) Cholinergic Nerve Terminal Acetylcholine (ACh) production synthesized from choline and acetyl-CoA by choline acetyltransferase acetyl-CoA is made in the mitochondria choline is transported into the nerve by choline transporter (CHT) Pathway Inhibitors hemicholinium: blocks the uptake of choline by inhibiting CHT vesamicol: inhibits vesicular acetylcholine transporter (VAT) preventing the storage of acetylcholine botulinum toxin: cleaves the SNAP proteins thereby preventing the presynaptic vesicles from docking at the terminal and releasing acetylcholine