Lecture 11 - synapses & neurotransmitters

Question 1

What are modulator transmitters?

Answer 1

acetylcholine, dopamine, serotonin

Question 2

Describe acetylcholine metabolism

Answer 2

ChAT (choline acetyltransferase) - good marker for cholinergic neurons
- Acetyl CoA produced by cellular respiration in mitochondria

Question 3

Where does ChAT live?

Answer 3

lives in cytoplasm of the presynaptic cholinergic neuron

ACh transported into vesicle by ACh transporter. When released into synaptic cleft, instead of acetylcholine being taken up by reuptake transporter, the Ach is destroyed in synaptic cleft by enzyme - acetylcholinesterase
- choline uptake into presynaptic cell by choline transport
- acetyl CoA - used in respiration

Question 4

What receptors does Acetylcholine act on?

Answer 4

• nicotine (ionotropic)
• muscarinic (metabotropic)
• Nicotinic (nAChRs) - ACh-gated Na+/Ca2+ channel, found at neuromuscular junction, CNS.
• Muscarinic (mAChRs): 5 types of GPCRs, found in CNS & autonomic nervous system. Recall Ioewi’s 1921 expeirment on the heart: the ‘vagusstoff’ was ACh.

M1,3,5: excitatory via Gq
M2,4: inhibitory via Gi/o

Question 5

Does the brain have more mAChRs or nAChRs?

Answer 5

• Brain has approximately 10-100x more mAChRs than nAChRs

Nicotinic receptors are ACh gated channels that when active allow in a positive current, which depolarised the postsynaptic neuron. Found at the neuromuscular junction

Question 6

What are muscarinic receptors?

Answer 6

GPCRs (G-protein-coupled receptors)

Question 7

Explain how acetylcholine is the neurotransmitter at the neuromuscular junction (NMJ)

Answer 7

nicotinic acetylcholine receptors receive the signal on muscles

• in vertebrates, the most abundant excitatory neurotransmitter is glutamate. In insects it is ACh.