Norepinephrine

Norepinephrine (NE) is the primary neurotransmitter of the sympathetic nervous system. Its effects are very similar to those of the hormone epinephrine, released by the adrenal medulla.

Role in the Central Nervous System

NE is used by modulatory system neurons in the locus coeruleus in the reticular activating system to affect arousal, anxiety, etc.

acts on β-adrenergic receptors on pyramidal cells, with little effect on its own; instead, primes cell for more powerful response to excitatory input such as glutamate
- one way it does so by increasing phosphorylation of K channels, decreasing their opening and increasing the excitability of cells

Norepinephrine (NE) is released by most postganglionic cells of the SNS, where it binds to a variety of receptors.

Adrenergic Receptors
	Receptor Locations	Physiological Effects	Intracellular effects	Agonist	Antagonist
α1	smooth muscle cells	peripheral vasoconstriction	increases IP₃, DAG, and calcium	phenylephrine	prazosin
α2	presynaptic adrenergic nerve terminals, platelets, lipocytes, SMCs	negative feedback on NE secretion; platelet aggregation	inhibits adenylate cyclase, decreasing cAMP	clonidine	Yohimbine
β1	cardiomyocytes, kidney		stimulates adenylate cyclase, increasing cAMP levels	isoproterenol, dobutamine	atenolol, metoprolol
β2	lung, intestine	bronciodilation dec. intestinal motility		albuterol, salbutamol
β3