Lecture 6- Neurotransmitters and Receptors

Question 1

What are the three types of neurotransmitters?

Answer 1

• Classical neurotransmission= Small molecule neurotransmitters
• Gaseous neurotransmission= gaseous transmitters
• Neuropeptide transmission= neuropeptides

Question 2

What type of neurotransmitter is nitric oxide?

Answer 2

Gaseous neurotransmitter

Question 3

How does nitric oxide word as a neurotransmitter?

Answer 3

• In presynaptic axon terminal Arginine is converted to Citrulline via the catalyst nitric oxide synthase.
• During this process nitric oxide is produced and because this is lipid soluble it can freely diffuse across membranes into neighbouring cells
• The only cells however that it will have an effect on are cells that contain soluble guanylyl cyclase. NO binds to this and causes the breakdown of GTP to cGMP which is a cellular second messenger.

Question 4

What is required in neighbouring cells for the gaseous neurotransmitter NO to have an effect?

Answer 4

soluble guanylyl cyclase

Question 5

What is CO and what is it produced by?

Answer 5

• Another gaseous neurotransmitter

- Made very similar to NO but by the heme oxygenase

Question 6

What is the most common excitatory neurotransmitter?

Answer 6

glutamate

Question 7

What are the four steps invovled at glutamatergic synapses?

Answer 7

1. Synthesis
2. Packaging
3. Exocytosis
4. Recycling

Question 8

What is invovled in the synthesis phase of glutamatergic synapses?

Answer 8

Glutamine (inactive form) is converted to glutamate by glutaminase

Question 9

How is glutamate packaged?

Answer 9

Glutamate is packaged into vesicles through vesicular glutamate transporters however this requires going against its concentration gradient (there is already a high concentration of glutamate inside). Therefore ATpase is required which breaks down into Hydrogen and ADP + P (releasing energy).

Question 10

How is glutamate exocytosed?

Answer 10

The vesicles merge with membrane of presynaptic vesicle either via full fusion or kiss and run. Glutamate crosses the synaptic clef and binds to glutamate receptors in the post synaptic cell membrane in order to have their effect.

Question 11

Why don’t we want glutamate sitting in the synaptic clef for longer than it is needed and what is the solution to this?

Answer 11

would

• Would get endless activation.
• To prevent this glutamate is recycled. It is taken up into glial cells by excitatory amino acid transporters 1+2. Glutamate is then synthesized back into glutamine (inactive version) via glutamine synthase and this glutamine travels back into the presynaptic terminal ready for the process to start again.

Question 12

How do excitatory amino acid transporters work to get glutamate into glial cells (during recycling)?

Answer 12

Because glutamate would have to go against its concentration gradient the process is coupled with ions (sodium and hydrogen). Chloride is also invovled.

Question 13

What do glutamate receptors consist of?

Answer 13

3 transmembrane domains, 4 subunits (alpha, beta, gamma, delta)

Question 14

What does changing the composition of the glutamate receptor subunits do?

Answer 14

It alters and changes the responses you can get

Question 15

Assertion question:-
Gaseous neurotransmitters act on receptors in the synaptic cleft
BECAUSE gaseous neurotransmitters freely diffuse across the cell
membrane.
Answer:-
A. if both statements are true, and the second causes the first.
B. if both statements are true but the second does not cause the first.
C. if the first statement is true and the second is false.
D. if the first statement is false and the second is true.
E. if both statements are false.

Answer 15

D.

Question 16

What are the two types of receptor present on the post-synaptic membrane utilized in classical neurotransmission?

Answer 16

Ionotropic and G-protein coupled receptors

Question 17

How do ionotropic receptors work?

Answer 17

• Neurotransmitter binds to a receptor
• This receptor also acts as an ion channel which becomes open upon binding
• Ions then flow across the membrane down their concentration gradient and can modulate the resting membrane potential

Question 18

What is another word for the neurotransmitter that binds to the ionotropic receptor?

Answer 18

Ligand

Question 19

What are g-protein coupled receptors also called?

Answer 19

Metabotropic receptors

Question 20

How do G-protein coupled receptors work?

Answer 20

• A neurotransmitter binds to a membrane receptor
• This causes G-protein subunits (alpha, beta, gamma) to become activated
• These protein sub units directly or Intracellular messengers (2 step- effectors) modulate the activity of ion channels to open them
• Ions then flow across the membrane down their concentration gradient (either in or out) and effect the membrane potential

Question 21

What requires the use of a G-protein coupled receptor?

Answer 21

Acetylcholine, biogenic amines, neuropeptides, purines

Question 22

What are cys-loop receptors made of?

Answer 22

• Four transmembrane domains

- 5 subunits (again composition alters what ions we can transport and therefore the response we get)

Question 23

Are cys-loop receptors all excitatory?

Answer 23

No some are excitatory, some are inhibitory depending on selectivity