Week 1 Flashcards
There are excitatory and inhibitory neuron terminals. Name one excitatory NT, two inhibitory NTs, and three NTs that can be excitatory or inhibitory
Excitatory: Glutamate
Inhibitory: dopamine, GABA
Both: Acetylcholine, serotonin, norepinephrine
What is the difference between the direct and indirect actions of NTs?
Direct action - neurotransmitters bind to and open ion channels. Promotes rapid responses by altering membrane potential.
Indirect action - neurotransmitter acts through intracellular second messengers, usually G protein pathways. Broader, longer-lasting effects
What are the two types of membrane channels? Describe them.
Voltage-gated: opens and closes in response to voltage changes across the membrane (voltage gated sodium channels; lidocaine)
Ligand-gated (ionotropic): a hormone, drug, or NT binds to the protein and the channel opens up (glutamate and ACh receptors)
What are the two different types of receptors on neurons? Describe them.
Ligand gated (ionotropic) - action is immediate and brief. Some are excitatory and open channels for small cations. Some are inhibitory and allow Cl- influx or K+ efflux to cause hyperpolarization.
Metabotropic - Not directly linked to ion channels. Initiates biochemical processes (G-protein mechanisms) that mediate more long-term effects and modify the responsiveness of the neuron. NT acts as the first messengers which activates a second messenger that in turn changes the excitability of a neuron.
What are the two types of metabotropic receptors? Describe them.
Membrane-delimited: occur entirely in plane of membrane. When G-proteins interact with Ca++ channels, they inhibit channel function (presynaptic inhibition). When G-proteins interact with K+ channels, they open (activate) channels causing postsynaptic inhibition.
Diffusible second messengers: beta-adrenergic receptors and cAMP . (This takes a lot more time to cause an effect than membrane-delimited)
What’s the difference between an autoreceptor and a heteroreceptor?
Autoreceptor - receptors on an axon terminal through which the neuron’s own NT can influence the function of the terminal (usually inhibitory) (such as D2)
Heteroreceptor - receptors on an axon terminal through which NTs from other neuronal types can influence the function of the terminal.
What does the chemical structure look like for dopamine, norepinephrine, and amphetamines?
Dopamine is a catecholamine that has an ethylamine group
Norepinephrine is a catecholamine with an ethyl group with a hydroxyl group and a terminal amine group
Amphetamine is a catecholamine with a site group with three carbons, one hydroxyl group, and a nonterminal amine group
Dopamine is synthesized from what amino acid precursor?
tyrosine
In order to produce dopamine.. once tyrosine is in the neuron, it is first converted to ___ by ____
DOPA (dihydroxyphenylalanine)
Tyrosine hydroxylase
Note that DOPA can be used to treat Parkinson’s
Once DOPA is produced it is converted to ____ by ____
DA (dopamine)
AAD (aromatic amino acid decarboxylase)
What happens once DA is produced in the neuron?
It is transported into vesicles via VMAT (vesicular monoamine transporter). It then can be released from the neuron
Once DA is released from the terminal, what are three fates of DA?
Bind to autoreceptor D2 - this will lead to decreased release of DA and decreased activity of tyrosine hydroxylase
Bind to post synaptic neuron receptors (heteroreceptors)
Be reuptaken into the presynaptic neuron via DAT (dopamine transporter)
What other molecules can go through the DAT?
Amphetamines can go through DAT. In this case, amphetamines enter the neuron while pumping out DA
Once DA is reuptaken into the presynaptic neuron via DAT, DA is metabolized into DOPAC by what enzyme?
Monoamine oxidase (MAO)
Describe the production of NE (norepinephrine)
Similar to production of DA. Once DA is produced and pumped into vesicles via VMAT, it is converted to NE by an intravesicular enzyme called DBH (dopamine beta hydroxylase)
Once NE is released from the presynaptic neuron, it has three similar fates to DA. It can bind to its autoreceptor ___, it can bind to ___ or ___ heteroreceptors on other neurons, or it can be pumped back into the presynaptic neuron via ____. _____ metabolizes NE in the neuron (similar to DA).
Alpha 2
Alpha or beta
NET (norepinephrine transporter)
Monoamine oxidase
What enzyme converts norepinephrine to epinephrine?
(PNMT) Phenylethenolamine-N-methyltransferase
What is a chatechol? What is a catecholamine?
A catechol is a benzene ring with two hydroxyl groups on adjacent carbons
A catecholamine is a catechol with a side chain with an amine group in it.
What cells mainly use epinephrine?
Adrenal medullary cells
Some CNS neurons
What does the structure of serotonin look like? Is it a catecholamine?
Two rings (one 6 carbon ring, one 5 carbon ring) with one hydroxyl group, and two amine groups
It is NOT a catecholamine
Serotonin is derived from what amino acid?
Tryptophan
In order to synthesize serotonin, the amino acid precursor ___ is converted to ____ by _____. Then, it is converted to ____ by ____
Tryptophan
5-hydroxyltryptophan (5HTP)
Tryptophan hydroxylase
Serotonin (5-hydroxyltryptamine)
AADC (amino acid decarboxylase)
What is the other name for serotonin?
5HT (5-hydroxyltryptamine)
What happens once serotonin is produced in the neuron?
It is pumped into vesicles via VMAT (vesicular monoamine transporter). Then the vesicles fuse with the membrane for release of the NT.
Similar to other NTs, serotonin can bind to an autoreceptor (___), bind to heteroreceptors, or be pumped back into the neuron (by ____)
5HT/1B
SERT (serotonin transporter)
What are SSRIs?
Selective serotonin receptor inhibitors. These drugs work on SERTs (serotonin transporters)
What is the function of dopamine beta hydroxylase?
Converts DA to NE in vesicles
___ +___ will yield ACh through the action of what enzyme?
Choline
Acetyl coA
ChAT (choline acetyl transferase)
Once ACh is produced in the neuron it is stored into vesicles through what transporter?
Vesicular ACh transporter
Note that it isn’t VMAT
Once ACh is released from the neuron it is quickly metabolized by ___ back to choline.
Acetylcholinesterase
True or false… there is a plasma ACh transporter in neurons
False! Just a choline transporter to pump choline back into the neuron
ACh can bind to what kinds of post synaptic receptors?
Muscarinic and nicotinic
How does the botulinum toxin work?
It prevents the release of ACh from neurons
Once ACh is released from the neuron, it may bind to what autoreceptor to decrease the release of ACh?
A muscarinic autoreceptor
GABA is an inhibitory NT whereas glutamate is an excitatory NT. How are their molecular structures similar?
Both have four carbons and a carboxyl group, and amine group
What is the precursor for producing glutamate?
Alpha keto gluterate (from citric acid cycle)
Alpha keto gluterate is converted to glutamate by the action of the ___ enzyme
Aminotransferase
Once glutamate is produced in the neuron, it is transported into vesicles by ___
Vesicular glutamate transporter
Once glutamate is released from the neuron, it may re-enter the neuron by the ___ transporter
Glutamate transporter
Once released from the neuron, glutamate binds to ____ (autoreceptor )
Metabotropic glutamate
Name two post synaptic receptors that glutamate binds to
AMPA/kainate
NMDA
Glutamate enters astrocytes through the glutamate transporter. Once in the astrocytes, glutamate is converted to ___ via the action of ____.
Glutamine
Glutamine synthetase
Once glutamine is produced in astrocytes, glutamine may enter the neuron and be converted to ___ through the action of ___.
Glutamate
Glutaminase
In order to produce GABA, ___ must first be produced
Glutamate
In the production of GABA, glutamate is converted to ___ through the action of ___
GABA
GAD (glutamate decarboxylase)
Once GABA is produced in the neuron, how does it enter vesicles?
Vesicular GABA transporter
Once GABA is released from neurons, it may renter the neuron through ____. Or it may bind to ___ and ___ post synaptic receptors. Or it may bind to its autoreceptor ___. Or it may enter ___.
GABA transporter
GABA-A or GABA-B
GABA-B
Astrocytes
Which postsynaptic GABA receptor is involved with chloride channels?
GABA-B
Once GABA enters astrocytes, it is converted to ___ through the action of ____
Succinate
GABA transaminase
What is an endocannabinoid? Give an example
Anandamide (binds to CB1 receptors)
They are natural endogenous NTs
True or false… nitric oxide doesn’t bind to receptors
True
Which histamine receptor is thought to function as an inhibitory heteroreceptor? Thus, activation of these receptors decreases the release of ACh, DA, NE, SER, and certain peptides?
H3
Endorphins bind to ___ receptors, causing a decrease in the release of ___. This mechanism can cause you to be happy.
Muscarinic
GABA
Name 7 neuropeptides
Neurotensin
Substance P
Somatostatin
Cholecystokinin
Vasoactive
Intestinal polypeptide
Neuropeptide Y
What does neurotensin do?
Acts as endogenous neuroleptic; regulates DA systems (inhibitory feedback)
What is nitric oxide? What does it do to vascular smooth muscle?
It is a gaseous signaling molecule
Relaxes vascular smooth muscle
In the autonomic nervous system, ACh binds to what kind of receptor on post ganglionic neurons
Nicotinic
True or false… ACh is used by both the sympathetic and parasympathetic pre-ganglionic fibers
True
True or false… drugs that alter ACh levels affect BOTH the sympathetic and parasympathetic systems
True
What other neurons act via nicotinic receptors?
Motor neurons innervating skeletal muscle
What types of NTs do post ganglionic sympathetic neurons use?
DA, NE, and EPI.
Most use NE
NE and EPI act on __ and __ receptors. What about DA?
Alpha and beta
DA activates D1, alpha, and beta
What NTs do post-ganglionic parasympathetic neruons use?
ACh
What receptors does ACh (released from post-ganglionic parasympathetic) neruons bind to?
Muscarinic receptors in most effector tissues
Nicotinic in somatic muscles
Name 5 specific receptors that the parasympathetic nervous system acts on.
M1
M2
M3
Nm
Nn
Describe where each of the following parasympathetic receptors are found.
M1 M2 M3 Nm Nn
M1 - Stomach
M2 - Heart (SA node, AV node, atria, ventricles)
M3 - GI tract (GI smooth muscle, secretory glands)
Nm- muscle (neuromuscular junction)
Nn - Neuronal (autonomic ganglia, adrenal medulla)
Name three agonists for parasympathetic muscarinic receptors
ACh
Bethanechol
Pilocarpine
If parasympathetic M1 receptors are activated by an agonist, what happens?
Acid secretion in the stomach increases
If M2 receptors are activated by an agonist, what happens?
SA node -> decrease HR
AV node -> decrease in conduction velocity
Atria -> decrease AP duration and contractility
Ventricles -> decrease in contractility
If M3 receptors are activated by an agonist, what happens?
GI smooth muscle - increase contractions (usually; except sphincters)
Secretory gland - increase secretions
Name two antagonists of the muscarinic receptors
Atropine
Scopolamine
Name two antagonists of Nm receptors
Succinylcholine***
D-tubocurarine
Name two antagonists of Nn receptors
Mecamylamine**
Trimethaphan
What are the two classes of neuromuscular blockers ? Describe them and give an example of each
Depolarizing (succinylcholine) - non-competitive. Acts as a nicotinic agonist and depolarizes/desensitizes the deuromuscualr endplate by opening up the NIC channels and keeps them open so that the neuron is depolarizer and unresponsive to another ACh challenge.
Non-depolarizing (tubucurare) - competitive. Competes with ACh at nicotinic receptors