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56 Cards in this Set

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two main neurotransmitters that operate in the autonomic system
acetylcholine
noradrenaline
all motor fibers leaving CNS release ___ which acts on ___ receptors
acetylcholine
nicotinic
all postganglionic parasympathetic fibers release ___, which acts on ___ receptors
acetylcholine
muscarinic
all postganglionic sympathetic fivers (with one exception:___) release ___, which may act on either ___ or ___.
(exception: sympathetic innervation of sweat glands - ACh acting on muscarinic receptors)
-noradrenaline - alpha or beta adrenoreceptors
inotropy
contractility
Voluntary nervous system -neurotransmitter
-agonist
-antagonist
Neurotransmitter: ACh
Agonist: nicotine
Antagonist: curare
Parasympathetic nervous system
-neurotransmitter
-agonist
-antagonist
Neurotransmitter: ACh
Agonist:
-at ganglion: nicotine
-at SM, glandular cell: muscarine
Antagonist:
-at ganglion: hexamethonium (C6)
-at SM, glandular cell: atropine
Sympathetic nervous system
-neurotransmitter
-agonist
-antagonist
Neurotransmitter:
-at ganglion: ACh
at SM, glandular cell: noradrenaline
Agonist:
-at ganglion: nicotine
-at SM, glandular cell: alpha, beta agonist
Antagonist:
-at ganglion: hexamethonium (C6)
-at SM, glandular cell: alpha, beta antagonist
Co-transmitters
Additional substances that are packaged with original neurotransmitter and released when we stimulate nerves. ATP is one important substance. It acts as a neurotransmitter in it’s own right.
Neuropeptide Y
36 amino acid peptide neurotransmitter found in brain and ANS
augments vasoconstrictor effects of noradrenergic neurons
Vasoactive Intestinal Peptide
28 amino acids
parasympathetic actions of vasodilation in GI tract, sweat, salivary glands, penis
Tyrosine Hydroxylase
an oxygenase, found in the cytosol of all cells containing catecholamines is the enzyme that catalyzes the rate-limiting step in the production of catecholamines

converts tyrosine to DOPA, which is then converted to dopamine, which is then converted to norepinephrine
AAADC
Aromatic Amino Acid Decarboxylase
catalyzes decarboxylation reaction that converts DOPA to dopamine, and 5-HTP to serotonin
VMAT
Vesicular Monoamine Transporter
Transport protein located in presynaptic cells that works on synaptic vesicles.
DBH
Dopamine Beta-Hydroxylase
Will convert dopamine to norepinephrine. When DBH is not present, the neurotransmitter will be dopamine.
Catecholamines
chemical compounds derived from the amino acid tyrosine - most abundant catecholamines are epinephrine, norepinephrine and dopamine
these are hormones that are released by the adrenal glands in situations of stress such as psychological stress or low blood sugar levels
VMAT1
-transports the monoamine neurotransmitters into synaptic vesicles
-in chromaffin cells, it is responsible for transporting newly synthesized epinephrine from cytosol back into chromaffin granules in prep for release
-also ships NE out of granules of chromaffin cells so that it can be acted upon by PNMT in the cytosol
Chromaffin Cells
-neuroendocrine cells found in the medulla of the adrenal gland
-secrete epinephrine, norepinephrine
-where the enzyme dopamine-hydroxylase catalyzes the conversion of dopamine to noradrenaline
PNMT
Phenylethanolamine N-methyltransferase
-an enzyme found in the adrenal medulla that converts Norepinephrine Epinephrine
Activation of the nicotinic receptors on the adrenal medulla will___.
Activate and release adrenaline.
Adrenaline is made by:
adding another methyl group to noradrenaline, done by PMNT in the cytosol of the adrenal medulla
Norepinephrine (noradrenaline)
-a catecholamine with dual roles as a hormone and a neurotransmitter
-synthesized from dopamine by dopamine β-hydroxylase
-released from the adrenal medulla into the blood as a hormone, and is also a neurotransmitter in the central nervous system and sympathetic nervous system where it is released from noradrenergic neurons
-along with epinephrine, underlies flight-or-flight response
Reserpine
Blocks VMAT, which normally transports free norepinephrine, serotonin, and dopamine from the cytoplasm of the presynaptic nerve into vesicles for subsequent release into the synaptic cleft. The unprotected neurotransmitters are then metabolized by MAO and therefore never reach the synapse.
MAO
Monoamine oxidases are enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. This deactivates the neurotransmitters.
NET/NAT
Neuroepinephrine Transporter
-monoamine transporter that transports the neurotransmitter noradrenaline from the synapse back to its vesicles for storage until later use
Uptake 1
presynaptic uptake
high-affinity
saturable
Na-dependent
Substrates: NA>A
Inhibitors: Imipramine, cocaine
Uptake 2
location: cell membranes of non-neuronal cells
low-affinity
not saturable
not Na-dependent
Substrates: A>NA
Inhibitors: corticosteroids
COMT
Catechol-O-methyl transferase
-an intracellular enzyme located in the postsynaptic neuron involved in the inactivation of the catecholamine neurotransmitters
-introduces a methyl group to the catecholamine
Pheochromocytoma
-neuroendocrine tumor of the adrenal medulla (originating in the chromaffin cells), or extra-adrenal chromaffin tissue that failed to involute after birth and secretes excessive amounts of catecholamines, usually epinephrine and norepinephrine
-can be detected by testing metanephrines in urine (product of COMT)
Tyramine
-monoamine compound derived from tyrosine
-can cause the release of stored monoamines, such as dopamine, norepinephrine, and epinephrine
Amphetamine
-a group of drugs that act by increasing levels of norepinephrine, serotonin, and dopamine in the brain
-has been shown to both diffuse through the cell membrane and travel via the dopamine transporter (DAT) to increase concentrations of dopamine in the neuronal terminal
Phenelzine
Monoamine oxidase inhibitor (MAOI) used as an antidepressant drug
-similar to other substrates of MAO
-MAO tries to oxidize phenelzine, which then binds covalently to the enzyme, thus inactivating it irreversibly
MAO-A
-preferentially deaminates norepinephrine and serotonin
-inhibited by clorgiline and befloxatone
MAO-B
-preferentially degrades benzylamine and phenylethylamine
-inhibited by: selegiline (deprenyl), rasagiline
Adrenergic Receptors
-two main groups?
-subtypes?
-class of G protein-coupled receptors that are targets of the catecholamines
-ligands are adrenaline and noradrenaline and are activated by these
-main groups: alpha and beta
-subtypes of alpha: alpha1 and 2
-subtypes of beta: beta1, 2, and 3
α1 receptor mechanism
α1 couples to Gq, which results in increased intracellular Ca2+ which results in e.g. smooth muscle contraction
α2 receptor mechanism
α2 couples to Gi, which causes a decrease of cAMP activity, resulting in e.g. smooth muscle contraction.
β receptor mechanism
β receptors couple to Gs, and increases intracellular cAMP activity, resulting in e.g. heart muscle contraction, smooth muscle relaxation and glycogenolysis
β1 agonist action
heart muscle contraction
β2 agonist action
smooth muscle relaxation
β3 agonist action
enhance lipolysis
Alpha receptors cause vaso___
Beta receptors cause vaso___
alpha = vasoconstriction
beta = vasodilation
Prazosin
-alpha-adrenergic blocker, which lowers blood pressure by relaxing blood vessels
-prazosin, specifically, is selective for the alpha-1 receptors on vascular smooth muscle. These receptors are responsible for the vasoconstrictive action of norepinephrine, which would normally raises blood pressure. By blocking these receptors, prazosin reduces blood pressure.
Phentolamine
-Regitine
-reversible, nonselective alpha-adrenergic antagonist
-primary action is vasodilation due to α1 blockade
-primary application is the control of hypertensive emergencies, most notably due to phaeochromocytoma
Isoprenaline
-structurally similar to epinephrine but acts selectively on beta receptors, activating β1 and β2 receptors equally
-primary use is for bradycardia or heart block. By activating β1-receptors on the heart, it induces positive chronotropic, dromotropic, and inotropic effects.
Propranolol
-a non-selective beta blocker mainly used in the treatment of hypertension
-blocks the action of epinephrine on both β1- and β2-adrenergic receptors
How does Clonidine lower blood pressure?
1. Presynaptic effect and reduced NE release from sympathetic post-ganglionic neurons.
2. CNS effect: activation of alpha-2 receptors in cardiovascular regulatory sites in medulla --> reduced sympathetic tone.
alpha-2 agonist
Phenylephrine
an α1-adrenergic receptor agonist causing vasoconstriction and smooth muscle contraction
Yohimbine
-A selective competitive α2 adrenergic receptor antagonist. The α2 receptor is responsible for sensing adrenaline and noradrenaline and telling the body to decrease its production as part of a negative feedback loop. Blocking α2 causes an increase in the release of NE.
-Yohimbine helps to raise libido.
Salbutamol (Albuterol)
A short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease.
Dobutamine
Direct stimulation of β1 receptors of the sympathetic nervous system. Specifically of the heart, increasing contractility and CO. Since it does not act on dopamine receptors to induce the release of NE (another α1 agonist), dobutamine is less prone to induce hypertension than is dopamine.
Atenolol
A β1 receptor selective antagonist, a drug belonging to the group of β-blockers.
Location of β1-Adrenergic receptors
mainly in the heart and in the kidneys
Location of β2-Adrenergic receptors
located mainly in the lungs, GI tract, liver, uterus, vascular smooth muscle, and skeletal muscle (note that there is a small population on the heart)
Location of β3-Adrenergic receptors
fat cells
Prazosin
Prazosin is an α-adrenergic blocker, selective for α1 receptors on vascular smooth muscle. These receptors are responsible for the vasoconstrictive action of NE, which would normally raise bp. By blocking these receptors, prazosin reduces blood pressure.