Neurotransmitters

Question 1

What factors define any given NT system?

Answer 1

• NT molecule
• synthetic machinery
• packaging
• reuptake and degradation mechanisms
• action

Question 2

What are the 3 criteria for a molecule to be a NT?

Answer 2

1. synthesis & storage in the presynaptic neuron
2. Released by presynaptic terminal in response to ↑[Ca++]
3. When applied, elicits/mimics the post-synaptic cell response

Question 3

What is immunocytochemistry?

Answer 3

Process for localising molecules to cells (identifying proteins)

Question 4

How can we localise classic NT vs neuropeptides?

Answer 4

Neuropeptides - we can look for the NT themselves

Classic NTs - can look for their synthesis enzymes

Can only look for proteins

Question 5

Briefly describe the aim/process of immunohistochemistry

Answer 5

Using the immune system to create antibodies against a particular sequence of Amino Acids.
* inject NT candidate
* purify antibodies from the blood
* fix a brain tissue section
* flood with antibodies & they will bind to the AA sequence

Question 6

What is in situ hybridization?

Answer 6

Detect cells when synthesis of a protein/peptide is taking place - by detecting mRNA that codes for that AA sequence

Question 7

How can NT release be studied?

Answer 7

Using a brain slice kept alive in vitro, stimulate synapses, collect & measure released chemicals.

Can also now use optogenetics

Question 8

How can synaptic mimicry be studied?

Answer 8

stimulate the neuron & record the results. Then release a drug & record the results.

Question 9

What are methods for identifying receptor subtypes?

Answer 9

• Ligand-binding methods - radioligand can show where the drug is binding
• Molecular analysis - can identify by their molecular/subunit composition

Question 10

What is Dale’s principle and is it true?

Answer 10

A neuron has only one neurotransmitter.
It is true for classic NTs

Question 11

Describe ACh synthesis in the presynaptic terminal

Answer 11

Choline + Acetyl CoA —ChAT–> ACh + CoA

ChAT = choline acetyltransferase [enzyme]

Question 12

Describe ACh degradation in the synaptic cleft

Answer 12

ACh –AChE–> Choline + Acetic acid

AChE = Acetylcholinesterase [enzyme]

Question 13

Where does Choline come from for ACh synthesis?

Answer 13

Choline transporters uptake choline from the synaptic cleft (left there by ACh breakdown by AChE)

Question 14

Describe the pathway of catecholaminergic NT synthesis & identify the common precursor

Answer 14

Common precursor - Tyrosine

Pathway:
Tyrosine
↓
L-Dopa
↓
Dopamine
↓
Norepinephrine
↓
Epinephrine

Question 15

What are the catecholamine NTs?

Answer 15

• Dopamine
• Norepinephrine
• Epinephrine

Question 16

What determines which NT is synthesised in a catecholaminergic neuron?

Answer 16

The enzymes - needs extra enzymes to get further down the pathway between tyrosine & epinephrine

Question 17

What is the precursor to serotonin?

Answer 17

Tryptophan

Question 18

How are the amino acid NTs related?

Answer 18

All part of the same synthesis pathway:

Glutamate
↓
Glycine
↓
GABA

Question 19

Which enzyme synthesises GABA from Glutamate?

Answer 19

GAD (glutamic acid decarboxylase)

Question 20

Describe ionotropic receptors

Answer 20

• fast transmission
• sensitive to chemicals/voltage
• regulate the flow of large currents
• differentiate between ions (specificity) but not as specific as Na/K channels etc
• 5 protein subumits (similarity in structure between different ionotropic receptor types)

Question 21

Describe AMPA receptors

Answer 21

• glutamate-gated channels
• cause EPSPs
• allows Na+ (inwards) & K+ (outwards) flow

Question 22

Describe NMDA receptors

Answer 22

• glutamate-gated channel
• causes EPSP
• Allows Na+ & Ca++ (inwards) & K+ (outwards)
• has Mg++ gate in place at resting Vm
• voltage & chemically dependent - requires glutamate binding PLUS strong depolarisation to remove Mg++ gate to open channel

Question 23

What is the general function of GABA-gated and glycine-gated channels?

Answer 23

major inhibitory ionotropic receptors

Question 24

Describe a GABA_A receptor

Answer 24

• Cl- channel
• inhibitory
• requires GABA to bind to open channel

Question 25

What are the 3 steps in gPCR transmission?

Answer 25

1. NT binds to gPCR 2. activation of G Protein 3. Activation of effector systems

Question 26

What are the 3 steps in gPCR transmission?

Answer 26

1. NT binds to gPCR 2. activation of G Protein 3. Activation of effector systems

Question 27

What is the basic structure of gPCRs?

Answer 27

single polypeptide with 7 transmembrane α-helices

Question 28

List some commonly mentioned gPCRs

Answer 28

* muscarinic receptors (M_1, M_2 etc) * GABA_B receptors * Dopamine receptors (D1, D2, D3 etc) * NE receptors (α1, α2, β1, β2, β3) * opiod receptors (µ etc)

Question 29

Where are inactive G proteins found?

Answer 29

floating around in the membrane (occasionally bumping into receptors)

Question 30

What are the 3 subunits of a G -protein, and how do they split?

Answer 30

α β γ split into Gα and Gβγ functional units

Question 30

What are the 3 subunits of a G -protein, and how do they split?

Answer 30

α β γ split into Gα and Gβγ functional units

Question 31

What are the 5 steps of G protein action?

Answer 31

1. G protein subunits together with α bound to GDP (inactive state) 2. G protein associates with activated gPCR, GDP exchanged for GTP 3. Gα dissociates from Gβγ, they act on other cellular systems 4. Gα inactivated when GTP converted to GDP 5. Gα recombines with Gβγ → reenters inactive state

Question 32

What is an example of a fast, localised G protein response?

Answer 32

G protein subunit acting on an ion channel

Question 33

What is a slow G protein response?

Answer 33

G protein subunit activating secondary messenger cascades (activation of downstream enzymes)

Question 34

How can different G Proteins have different effects when activated by the same NT?

Answer 34

Different G protein types - ie Gs is stimulatory, Gi is inhibitory.

Question 34

How can different G Proteins have different effects when activated by the same NT?

Answer 34

Different G protein types - ie Gs is stimulatory, Gi is inhibitory.

Question 35

Compare the activity of α2 and β receptor effects

Answer 35

Both activated when NE binds to gPCR. α2 = Gi receptor → inhibits Adenylyl cyclase β = Gs receptor → stimulates Adenylyl cyclase

Question 36

Describe the phospholipase C (PLC) second messenger cascade and the singificance of the end result

Answer 36

1. Activated G Protein stimulates PLC 2. Activated PLC splits PIP2 into DAG & IP3 3. DAG stimulated Protein Kinase C (PKC) 4. IP3 stimulates release of Intracellular Ca++ End result: This is another way to ↑[Ca++]

Question 37

What is the function of signal cascades?

Answer 37

signal amplification - ie 1 NT binding can then result in many channels being opened later (rather than 1:1 ratio of directly binding ion channel)

Question 38

What is signal divergence?

Answer 38

1 NT → lots of different responses (more than 1 receptor type activated)

Question 39

What is signal convergence?

Answer 39

Many NT → all eliciting the same response (different NTs with the same effect)