DSA Chemical Messengers & Excitotoxicity Flashcards
For membrane potentials, the ionic gradient is created by what two things?
- Selective permeability of membrane
- - Na/K ATPase
In the Na/K ATPase there are ______ Na out for every _____ K in.
3
2
***Remember, Na+ has high concentration outside cell, and K+ has high concentration inside cell. It’s moving against concentration gradient (has to use ATP).
What are “atypical” examples of cells that can create action potentials?
Pancreatic beta cells
Glial cells
Put the following steps of the synaptic transmission in order from first to last:
A. Calcium influx into terminal.
B. Release of NT into the cleft/trough.
C. Binding of NT to receptor.
D. AP in presynaptic cell arrives at presynaptic terminal.
E. Fusion of vesicle with membrane.
F. Depolarization opens presynaptic voltage-gated calcium channels.
G. Diffusion of NT across cleft/trough.
H. Binding to docking proteins that connect NT vesicles to membrane.
1) D.
2) F.
3) A.
4) H.
5) E.
6) B.
7) G.
8) C.
What are the two general categories of NT receptors?
Ionotropic
Metabotropic (or Serpentine)
With this type of NT receptor, the receptor is associated with an ion channel that opens in response to the binding of the NT – “Ligand-gated ion channel”.
Ionotropic
***i.e., Nicotinic cholinergic
With this type of NT receptor, the binding of the NT to the receptor activates a second-messenger system.
Metabotropic (Serpentine)
This type of Metabotropic receptor is the most common and stimulates adenylate cyclase.
Gs
This type of Metabotropic receptor inhibits adenylate cyclase.
Gi
This type of Metabotropic receptor produces DAG and IP3. It involves calcium release from intracellular stores.
Gq
This is the term for when the binding to receptor opens a cationic channel (sodium or calcium). There is then an influx of sodium or calcium, causing a depolarized membrane. This brings us closer to threshold and increases the probability for AP.
Excitatory Post-Synaptic Potential (EPSP)
***Same thing as End-Plate Potential for NMJ
This is the term for when binding to receptor opens chloride (anion) channels. There is then an influx of chloride, which hyperpolarizes the membrane and brings us farther away from threshold. This reduces the probability of AP.
Inhibitory Post-Synaptic Potential (IPSP)
Remember, in neurophysiology the location in the brain that “makes” the NT is the location of the…
Cell bodies
***Example was Serotonin. Their cell bodies lies within the Raphe Nuclei but their axons can go many other locations to synapse!
What is the difference between saying something “projects to” versus saying a “tract” or “bundle”?
Projects to is usually smaller.
Tracts or bundles are usually a substantial group of axons traveling together to the same location.
The monoamine class of NTs includes all of those that are created by modifying single amino acids. This group includes…
Epinephrine (adrenaline) Norepinephrine (noradrenaline) Dopamine Serotonin Histamine
Where do you find Norepinephrine?
Locus Ceruleus
***Remember, this is where the cell bodies for NE are found!
What is the function of Norepinephrine?
Wakefulness
Alertness
Where is Epinephrine found?
Medulla
Epinephrine and Norepinephrine are derived from what?
Tyrosine
What are the basic steps involved to produce Epinephrine?
Tyrosine — Dopamine — Norepinephrine — Epinephrine
This enzyme is the rate-limiting step for the conversion of Tyrosine to L-DOPA (dopamine).
Tyrosine Hydroxylase
What is the enzyme used to convert Norepinephrine to Epinephrine after it leaves the vesicles?
PNMT (Phenolethanolamine-N-methyl transferase)
Describe the steps of conversion from Tyrosine to Epinephrine in detail.
Tyrosine is converted to L-DOPA in the cytoplasm using Tyrosine Hydroxylase. L-DOPA is then moved into vesicles where Norepinephrine is made. The Norepinephrine then leaves the vesicles and PNMT converts it to Epinephrine. Epinephrine then moves back into vesicles for release.
***Remember, ONLY the enzyme for whatever NT you want to be released are present. If you’re releasing Norepinephrine then you won’t have PNMT, etc.
What are the proteins that move Epinephrine and Norepinephrine into the vesicles (against their concentration gradient)?
VMAT1
VMAT2
This inhibits the movement of Epinephrine and Norepinephrine into vesicles, which leads to synaptic failure. It was an early drug used to treat high BP.
Reserpine
Epinephrine and Norepinephrine action is limited by their reuptake from the synapse, followed by enzymatic degradation. What enzymes are used for this degradation?
Monoamine Oxidase
Catechol-O-methyl transferase
This enzyme used for degradation is on the outer surface of mitochondria. Its metabolites are released into the ECF.
Monoamine Oxidase
This enzyme used for degradation is in Glial cells and Post-synaptic membranes.
Catechol-O-methyl transferase
What type of receptors do Epinephrine and Norepinephrine bind to?
Metabotropic (Serpentine) receptors — Alpha-adrenergic or Beta-adrenergic
Where do you find Dopamine?
Basal Ganglia
Hypothalamus
Limbic System
What is the function of Dopamine?
Basal Ganglia = Motor control
Hypothalamus = Endocrine
Limbic System = Emotional control
How is Dopamine made?
From Tyrosine by using enzyme Tyrosine Hydroxylase
***Remember, precursor to Norepinephrine and Epinephrine
How do you limit the action of Dopamine?
By reuptake and catabolism by MAO and COMT
***Same as Epinephrine and Norepinephrine!
What does Dopamine bind to?
5 types of Metabotropic (Serpentine) receptors connected to G proteins
These Dopamine receptors increase cAMP and are involved in excitation of neurons.
D1 and D5 (called D1-like)
These Dopamine receptors decrease cAMP and are involved in inhibiting neurons.
D2 (has Potassium efflux)
D3 and D4 (called D2-like)
Where do you find Serotonin?
Brainstem Raphe Nuclei
Cerebellum
Hypothalamus and Limbic System
What is the function of Serotonin?
Brainstem Raphe Nuclei = Modification of motor activity
Cerebellum = Modification of motor activity
Hypothalamus and Limbic System = Mood
How is Serotonin made?
Derived from Tryptophan by using the enzyme Tryptophan Hydroxylase
How do you limit the action of Serotonin?
By reuptake and catabolism by MAO and COMT
***Same as NE, Epinephrine, and Dopamine
What are the receptors for Serotonin?
7 receptors –
6 Metabotropic (serpentine) receptors = 5HT 1, 2, 4, 5, 6, 7 1 Ionotropic receptor = 5HT 3
This Serotonin receptor is ionotropic and creates an influx of Na+. Its location is at the intersection of the Spinal Cord and Medulla, called the Area Postrema.
5HT 3
What is Area Postrema responsible for?
Neurons here are called Chemotactic Trigger Zone and when there is an influx of Na+ it illicits vomiting.
This Serotonin receptor is metabotropic (serpentine) and has an anti-depressant effect.
5HT 6
Where is Histamine found?
Tuberomammillary Nucleus of Hypothalamus
What is the function of Histamine?
Wakefulness
***Strongly associated – Anti-histamines cause drowsiness
How is Histamine made?
Derived from Histidine by the enzyme Histidine Carboxylase
How do you limit the actions of Histamine?
By reuptake and then catabolism by Diamine Oxidase and COMT.
***Remember, the other NTs were Monoamine Oxidase and COMT!
What are the receptors for Histamine?
3 Metabotropic (serpentine) receptor types – H1, H2, H3
This Histamine receptor activates PLC and is strongly associated with allergic reactions.
H1
This Histamine receptor increase cAMP and is associated with gastric acid release.
H2
This Histamine receptor is rare. It is presynaptic and decreases Histamine release.
H3
T/F. There is more H2 and H3 in the brain than H1. H3 is involved in wakefulness.
False. There is more H1 and H3 in the brain than H2. H1 is involved in wakefulness.
How do non-drowsy anti-histamines work?
They work because they do not cross the BBB.
Where is ACh found in the brain?
Midbrain and Pons
Striatum of the Basal Ganglia (Caudate and Putamen)
What is the function of ACh in the brain?
Midbrain and Pons = Arousal/Wakefulness and REM sleep
Striatum of Basal Ganglia = Control of voluntary motion
How is ACh made?
By combining Choline and Acetate
ACh is moved into clear vesicles via what protein?
VAChT (Vesicular ACh Transporter)
VAChT moves ACh against its concentration gradient into the vesicles. This is why presynaptic vesicles have a lot of _________, because this requires a lot of energy!
Mitochondria
How do you limit the actions of ACh?
Removed from synaptic trough via Acetylcholinesterase that is bound to the postsynaptic membrane.
What are the receptors used for ACh?
Muscarinic – Metabotropic (serpentine) has 5 subtypes
Nicotinic – Ionotropic
This muscarinic receptor for ACh is neuronal and increase IP3/DAG, which in turn increases Calcium (Gq).
M1
This muscarinic receptor for ACh is cardiac and decreases cAMP which leads to an efflux of K+ (Gi).
M2
This muscarinic receptor for ACh is for smooth muscle of bronchi and vasculature, and endothelial cells of vasculature (NO). It increases IP3/DAG, which increases Calcium (Gq).
M3
This muscarinic receptor for ACh is a presynaptic auto receptor and at the Striatum of Basal Ganglia. It decreases cAMP (Gi). Involved in how much ACh is released from a neuron.
M4
This muscarinic receptor for ACh is involved with cerebrovasculature and dopaminergic neurons of basal ganglia. It increases IP3/DAG.
M5
This type of ACh receptor is located at NMJ, synapses between pre- and post-synaptic ganglionic cells in autonomic ganglia, and other central synapses.
Nicotinic receptors
Nicotinic receptors for ACh have different subunits (NOT subtypes). Changing the subunits changes the properties of the channel. In some central synapses, it creates a nicotinic channel that allows more ________ in.
Calcium
T/F. ACh involved in the ANS and NMJs is different from ACh involved in the brain.
True
What are the two major inhibitory amino acids?
GABA (Gamma-amino-butyric acid)
Glycine
This is the major inhibitory amino acid NT in the CNS. It is widely distributed throughout higher levels of the CNS.
GABA
What areas of the CNS have GABA?
Cortex
Cerebellum
Basal Ganglia
Spinal Cord – has very little of it
What is the role of GABA?
It has multiple roles (too many to name) but it is critical in consciousness, motor control, and vision (retina).
How is GABA made?
Derived from Glutamate by the enzyme Glutamate Decarboxylase (GAD)
How is GABA transported into vesicles?
By the protein VGAT (Vesicular GABA Transporter)
How do we limit the action of GABA?
Removed from the synapse via GAT (GABA Transporter)
There are two forms of GAT (removes GABA from synapse). What are they?
GAT1
GAT2
This type of GAT is located on the presynaptic terminal and takes the GABA up as is. The GABA is then repackaged into vesicles to be used again.
GAT1
This type of GAT is located on glial cells (astrocytes) surrounding the synapse. The GABA is taken up and converted to Glutamine then released into the ECF. From here it will be taken up by the presynaptic terminal and recycled into GABA.
GAT2
What are the types of GABA receptors?
GABA-A = Ionotropic GABA-B = Metabotropic
This type of GABA receptor is ionotropic and causes Cl- conductance. Activation produces IPSP in adult neurons.
GABA-A
There are multiple binding sites that modulate for GABA-A receptors, which are…
- Benzodiazepine site
- Ethanol
- Certain steroids
This binding site on GABA-A receptors will increase the amount of Cl- to enter the cell and hyperpolarize it. Often used as sedatives.
Benzodiazepine site
It appears there are a large number of extra-synaptic GABA-A receptors up in the higher CNS, especially the cortex. These receptors are believed to be the site of action for a number of general __________, including propofol.
Anesthetics
This type of GABA receptor is metabotropic and is Gi/Go coupled. It activates a K+ channel (GIRK) and closes down or inhibits a Calcium channel.
GABA-B
Where is GABA-B receptors located?
Presynaptic
Postsynaptic
Presynaptic GABA-B receptors regulate ________ release and postsynaptic GABA-B receptors inhibit the postsynaptic cell.
Neurotransmitter
GABA-B receptors are very important in modifying…
Motor tone
This inhibitory amino acid is found in the lower CNS, mainly the Spinal Cord and Brainstem (Medulla).
Glycine
This inhibitory amino acid mediates many spinal inhibitions.
Glycine
How is Glycine produced?
It is an unmodified amino acid.
How do we limit the action of Glycine?
Using GAT proteins (GAT1 and GAT2) to recycle it.
***Same as GABA!
What type of receptor is used for Glycine?
Only one – GlyR (ionotropic)
The Glycine receptor, GlyR, is ionotropic and causes an influx of ________ and leads to IPSP on post-synaptic cell. Ethanol and general anesthetics bind to it and potentiate.
Chloride
This binds to GlyR and blocks it, causing convulsions. Also known as rat poison!
Stychnine
All synaptic vesicles contain _______, which led to the debate that it was required for metabolic function (some NT synthesis is completed in vesicles). It was recognized as a co-transmitter first.
ATP
ATP is made by _________ (remember the pre-synaptic terminal has many of these).
Mitochondria
ATP is stored in vesicles by what protein?
VNUT
ATP is stored in vesicles then released in the synapse. What are the catabolic steps of it in the synaptic trough?
ATP — ADP — Adenosine
Where are purines (ATP, ADP, Adenosine) found?
Virtually everywhere in the CNS, but especially in the:
Cortex
Cerebellum
Hippocampus
Basal Ganglia
Purines have two major classes of receptors, which are…
P1
P2
This type of purine receptor is metabotropic and has Adenosine as its ligand. It is in post-synaptic and pre-synaptic locations.
P1 (A receptors)
This location of the P1 (A receptors) are responsible for sleep induction and general inhibition of neural function.
Post-synaptic locations
This location for P1 (A receptors) are responsible for inhibition of neurotransmitter release.
Pre-synaptic locations
There are two types of P2 receptors, which are…
P2X – Ionotropic
P2Y – Metabotropic
P2X receptors (ionotropic) has ________ as its ligand and contains many subtypes.
ATP
P2Y receptors (metabotropic) is Gi/Gq coupled and its ligands are…
ATP
ADP
UTP
UDP
What are the functions of P2 receptors?
Learning and memory (co-release with EAA)
Modification of locomotor pathways
Peptide neurotransmitters are made in the soma and transported down the axon via fast axonal transport. There are several types of these transmitters, but the one we are worried about is…
Opioids
The opioids are a family of peptides that include…
Endorphins
Enkephalins
Dynorphins
Nociceptin
Where are Opioids located?
Basal Ganglia
Hypothalamus
Pons and Medulla
What are the general functions of Opioids?
Modification of nociceptive inputs (Cutaneous senses)
Mood/Affect (Neurophysiology of Emotion/Drug Addiction)
There are four precursor molecules for Opioids, which are…
Proopiomelanocortinin (POMC)
Pro-enkephalin
Pro-dynorphin
Orphanin FQ
This Opioid precursor molecule makes ACTH and B-Endorphins.
POMC (Proopiomelanocortinin)
The Opioid precursor Pro-Enkephalin has two types composed of five amino acids each. The first four amino acids in the two types are the same, but the last amino acid is different. What are the two types and their amino acids?
Met-Enkephalin (Tyr-Gly-Gly-Phe-Met)
Leu-Enkephalin (Tyr-Gly-Gly-Phe-Leu)
This Opioid precursor gives rise to 3 molecules of Leu-Enkephalin and Dynorphin.
Pro-dynorphin
This Opioid precursor gives rise to Nociceptin.
Orphanin FQ
How are opioids made?
Standard protein synthesis in the cell body.
How is the action of Opioids regulated?
They are removed from the synaptic trough/cleft via reuptake and then catabolized by Enkephalinase (only Enkephalins) and Aminopeptidase (all others, non-specific).
What are the types of Opioid receptors?
Mu receptors – Metabotropic
Kappa receptors – Metabotropic
Delta receptors – Metabotropic
What are the activation causes of Mu receptors (Opioids)?
Analgesia (blunting of pain perception) Respiratory depression Euphoria Constipation Sedation
What are the activation causes of Kappa receptors (Opioids)?
Analgesia
Dysphoria
What are the activation causes of Delta receptors (Opioids)?
Analgesia
***It is hard to find a ligand that only binds to Delta receptors, usually bind to Mu receptor too!
All Opioid receptors are (IONOTROPIC/METABOTROPIC) and activate second messenger systems with ligand binding. They all connect Gi/Go proteins.
Metabotropic
This Opioid receptor leads to an increase in potassium efflux and hyperpolarization.
Mu receptors
This Opioid receptor decreases Calcium influx.
Delta receptors
Kappa receptors
This is another system that we identified based on the effects of exogenous chemicals (THC).
Endocannabinoids
What are the identified endogenous cannabinoids?
Anandamide 2 AG (2-Arachidonylglycerol)
Where are Endocannabinoids distributed?
Broadly in the CNS, but mainly:
- Basal Ganglia
- Spinal Cord
- Cortex
What are the functions of Endocannabinoids?
Basal Ganglia = Mood and Motor performance
Spinal Cord = Modulation of nociception
Cortex = Neuroprotection
How are Endocannabinoids synthesized?
Derived from membrane lipids (Arachidonic Acid) in the presynaptic terminal.
T/F. The synthesis of Anandamide and 2-AG is the same and uses the same enzymes.
False. They use separate pathways.
How is Anandamide synthesized?
Derived from NAPE (N-arachidonoyl phosphatidyl ethanol)
How is 2-AG synthesized?
Derived from arachidonoyl-containing PIP2 (phosphatidyl inositol bis-phosphate)
2-AG is the major source for _________ _________ in certain tissues, especially the brain. However, we have to be careful because pharmacological manipulation of 2-AG production has wide reaching effects beyond those of the Endocannabinoid system. Can have serious side effects.
Arachidonic Acid
This type of Cannabinoid receptor is metabotropic and has a neuronal location and its activation is associated with the psychoactive responses to the Cannabinoids. In humans, it’s a 472 amino acid peptide coupled to G-proteins.
CB1
This type of Cannabinoid receptor has polymorphisms that are linked to occurrence of obesity, ADHD, schizophrenia, and depression in Parkinson’s disease. It can also form a heterodimer with other NT receptors including dopamine and orexin.
CB1
The CB1 receptor has “uniform” and “non-uniform” distribution in CNS neurons. In “uniform” distribution, the receptors are not on specific neurons but are spread out. What are the locations of “uniform” distribution?
Striatum Thalamus Hypothalamus Cerebellum Lower brain stem
The CB1 receptors has “uniform” and “non-uniform” distribution in CNS neurons. In “non-uniform” distribution, the receptors are associated with specific neuron types. What are the locations of “non-uniform” distribution?
Cortex
Amygdala
Hippocampus
CB1 receptors are largely (PRE/POST)-synaptic and are generally away from the active zone where vesicles are. There is greater density at inhibitory synapses.
Pre-synaptic
CB1 receptors bind _______ and _______ with high affinity.
AEA (Anandamide)
2-AG
The CB1 receptor is relevant for neurophysiology. It is found on pre-synaptic terminals of ______ and ______ releasing synapses. This reduces the release of these NTs via a Gi coupled protein. AEA and 2-AG are equally effective when binding to it.
EAA
GABA
This type of Cannabinoid receptors were initially reported as peripheral receptors, found primarily on macrophages. More detailed studies have found them in the brain, but on the microglia.
CB2
CB2 receptors also have neuronal location (dendrites and within soma) but are usually associated with _______ injury.
Nerve
CB2 receptors are highly inducible in response to injury or _________.
Inflammation
***If there is an injury, CB2 receptors will appear on the neurons.
CB2 receptors bind ______ better than ______.
2-AG
AEA
There are two different paths for Endocannabinoid degradation, which are…
Hydrolysis
Oxidation
Hydrolysis of Endocannabinoids are prevalent in neurons. AEA and 2-AG are degraded via hydrolysis in two different pathways, which are…
AEA – degraded by FAAH (Fatty Acid Amide Hydroxylase)
2-AG – degraded by MAGL (Mono-acyl glycerol lipase)
What is unique about FAAH, the enzyme that hydrolyzes AEA?
It exists in two forms. Some people have a mutation in it, causing them to have lots of AEA. These people have tremendous pain resistance.
The oxidation of Endocannabinoids (both AEA and 2-AG) can be done by what enzymes?
Cyclooxygenase
Lipoxygenase
What are the two Excitatory Amino Acids (EAA)?
Glutamate
Aspartate
What is Glutamate derived from?
Alpha-ketoglutarate
Aspartate is often co-localized with Glutamate, but it serves as NT on its own in the _______ _______ and _________ cells.
Visual cortex
Pyramidal
T/F. The metabolic and transmitter pools of Glutamate and Aspartate are strictly separated.
True
T/F. EAAs are the most important excitatory NT system in the brain, and their location is widely distributed throughout the CNS.
True
EAA receptors can be either ionotropic and metabotropic. What are the different ionotropic receptors?
NMDA receptors
Non-NMDA receptors = AMPA and Kainate
What is the exogenous and endogenous agents that bind to NMDA receptors?
Exogenous = NMDA Endogenous = Glutamate and Aspartate (EAAs)
When the NMDA receptors are activated, what does it allow an influx of?
Calcium
For the NMDA receptors, _________ is a required co-agonist for the EAA to open the channel. It has its own binding site.
Glycine
This binding site in NMDA receptors is within the channel itself. It blocks the channel at resting membrane potential and stays in place even if EAA and Glycine have both bound and opened the channel.
Magnesium
This is a binding site that also blocks the channel of the NMDA receptor. It is internal to the Magnesium binding site, and works the same way that Magnesium does in the channel.
PCP
***Horse tranquilizer!
The Non-NMDA receptors allow an influx of what when EAAs bind?
Na+
AMPA is a type of Non-NMDA receptor. What are its exogenous and endogenous ligands that activate it?
Exogenous = AMPA Endogenous = Glutamate and Aspartate
These bind to a site on the extracellular face of the AMPA receptor. It reduces the amount of Na+ that enters the cell.
Benzodiazepines
***These are sedatives!
This Non-NMDA receptor is activated after EAA binds, causing an influx of Na+ and a little bit of Calcium.
Kainate
Activation of the Non-NMDA receptors produces a typical ________ with a relatively short onset and duration.
EPSP (Excitatory Post-synaptic Potential)
Activation of the NMDA receptors produces a “long
latency EPSP with a long duration. Why is this?
Due to the Mg++ blocking of the channel.
When EAA binds to NMDA and Non-NMDA receptors, the Non-NMDA receptors open first allowing Na+ into the cell. This depolarizes the cell, which forces the ________ out of the NMDA receptor allowing Calcium to enter the cell.
Mg++
T/F. Non-NDMA receptors do exist on pre-synaptic membranes without NMDA receptors in some systems.
False. Non-NMDA receptors do exist on POST-synaptic membranes without NMDA receptors in some systems.
These EAA receptors can be found on a lot of synapses alone. Involved with primary sensory afferents and upper motor neurons.
Non-NMDA receptors
These EAA receptors are not on every synapse and are critical in short- and long-term memory formation. Involved in synaptic plasticity.
NMDA receptors
What are the types of EAA metabotropic receptors?
Group 1 = Gq coupled (increased IP3/DAG)
Groups 2 and 3 = Gi coupled (decreased cAMP)
What is the function of presynaptic EAA metabotropic receptors?
Control NT release
What is the function of postsynaptic EAA metabotropic receptors?
Learning
Memory
Motor systems
EAAs can be very dangerous cells in large amounts. To remove them, they are taken into _______ cells surrounding the synapse.
Glial
Once taken into Glial cells, the EAA (in this case Glutamate) is converted to _________ and released into the ECF where it is taken up by the presynaptic neuron and converted back to Glutamate to be used again.
Glutamine
NMDA receptor activation can lead to the production of _______ _______.
Nitric Oxide (NO)
NMDA receptors allow an influx of Calcium. Once Calcium is in the cell it binds to _________ and activates the enzyme ________ ________ ________.
Calcineurin
Nitric Oxide Synthase (NOS)
Once activated, NOS will take the amino acid _________ and cleave NO off from it. _________ is also a by-product.
Arginine
Citrulline
_______ _______ is incredibly lipid-soluble and will diffuse out of the cell and go back into the presynaptic neuron. It can have many effects depending on the type of neuron.
Nitric Oxide (NO)
What is the function of NO in the hippocampus and cerebellum?
Memory (long-term potentiation)
What is the function of NO in the pons and medulla?
Cardiovascular and respiratory control
What is a non-neural function of NO immunologically?
Macrophages make NO because it is toxic and releases it in high concentrations.
What is a cardiovascular non-neural function of NO?
Produces vasodilation (relaxes smooth muscle – increases blood flow)
***Viagra will replicate the effects of NO using Cyclic GMP in this way, just longer lasting!
What is the downside of NO?
It is very unstable (has half-life of about 5 seconds). This leads to the production of free radicals, which are toxic to neurons in high concentrations.
