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Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS SEcTIoN II 239

Autonomic drugs Release of norepinephrine from a sympathetic nerve ending is modulated by NE itself, acting on
presyn aptic α 2 -autoreceptors Ž negative feedback.
Amphetamines use the NE transporter (NET) to enter the presynaptic terminal, where they utilize
the vesicular monoamine transporter (VMAT) to enter neurosecretory vesicles. This displaces NE
from the vesicles. Once NE reaches a concentration threshold within the presynaptic terminal,
the action of NET is reversed, and NE is expelled into the synaptic cleft, contributing to the
characteristics and effects of  NE observed in patients taking amphetamines.
CHOLINERGIC NORADRENERGIC

AXON AXON
Tyrosine
Choline
Tyrosine
Choline+ DOPA
Acetyl-CoA
Dopamine
ChAT
Reserpine - VMAT Release-modulating
ACh
receptors
Ca 2+ AT II
NE
+ +
ACh
Ca 2+ - α 2
+
Amphetamine, + Reuptake
Botulinum - ephedrine
toxin NET
Cocaine, TCAs, - Negative feedback
Choline + amphetamine
acetate NE
Di usion,
metabolism
ACh
receptor -
AChE inhibitors
AChE Adrenoreceptors α or β

POSTSYNAPTIC MEMBRANE POSTSYNAPTIC MEMBRANE

represents transporters.

FAS1_2019_05-Pharmacology.indd 239 11/7/19 4:08 PM