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)