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3rd Year Biomed > Neuroscience - Classical and peptide neurotransmitters > Flashcards

Neuroscience - Classical and peptide neurotransmitters Flashcards

1
Q

What are the 5 criteria for an effective neurotransmitter?

A

1) Must be synthesised in the neuron from which it is released
2) Presynaptic stimulation leads to release
3) Application at postsynapse much have same effect as at presynapse
4) Agents that block the postsynaptic response should also block the exogenously applied putative transmitter
5) Response must be terminated rapidly

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2
Q

What is the lifecycle of a classical neurotransmitter

A

1) Accumulation of precursor in neuron

2) Precursor enzymatically metabolised to yield
mature transmitter

3) Uptake into vesicle by vesicular transport
4) Release by regulated exocytosis
5) Binding to postsynaptic receptor or presynaptic modulatory receptor
6) Re-uptake into nerve terminal or glia by plasma membrane transporter
7) Enzymatic degradation in synaptic cleft or nerve terminal
8) Diffusion from active site

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3
Q

When was acetylcholine first identified and classified as a neurotransmitter?

A
  • Identified in 1913 by Henry Dale
  • classified as a neurotransmitter in the 1920s be Otto Loewi and Dale
  • Both won the nobel prize in 1936
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4
Q

How is acetylcholin synthesised? What is the enzyme?

A
  • Choline acetyltransferase (ChAT)
    > Transfers acetyl group from acetyl CoA to choline
  • Excess ChAT in nerve terminal
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5
Q

How is acetylcholine degraded?

A
  • Breakage of ester bond of ACH
  • Split into choline and acetate
  • Choline is taken back up in pre-synaptic nerve terminal by choline transporter
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6
Q

What enzyme catalyses the breakdown of acetylcholine? Where is it found?

A

Acetylcholinesterase

  • serine hydrolase
  • inserted into post-synaptic membrane via short glycophospholipid or long collagen tails
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7
Q

What is a mutation in either enzyme associated with?

A

Associated with congenital myasthenic syndromes

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8
Q

What are the 4 biogenic amines? When were they discovered?

A

1) Noradrenaline - 1946
2) Dopamine - identified as neurotransmitter in 1950s
3) Serotonin - 1930s
4) Histamine identified as transmitter in 1970s

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9
Q

What are the catecholamines?

A

Dopamine and noradrenaline

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10
Q

Describe catecholamine synthesis from the phenylalanine precursor

A 
Phenylalanine
Tyrosine
3,4-dihydroxyphenylalanine (DOPA)
Dopamine
Noradrenaline
Adrenaline
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11
Q

What enzyme catalyses each step?

A

1) Phenylalanine to Tyrosine
- phenylalanine hydroxylase (PAH)

2) Tyrosine to DOPA
- Tyrosine hydroxylase

3) DOPA to Dopamine
- DOPA decarboxylase

4) Dopamine to noradrenaline
- Dopamine-beta-hydroxylase

5) Noradrenline to adrenaline
- Phenylethanolamine N-methyltransferase

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12
Q

What type of enzymes are phenylalanine hydoxylase, tyrosine hydroxylase and dopamine-beta-hydroxylase?

A

Monooxygenases

- incorporate oxygen into an amino acid subtrate

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13
Q

What disorders are defects in PAH and TH associated with?

A
  • Defects in PAH causes phenylketonuria (PKU)

- Defects in TH associated with dystonia and infantile parkinsonism

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14
Q

How does DOPA decarboxylase work?

A

Decarboxylates aromatic L-amine acids

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15
Q

What 2 enzymes are involved in Catecholamine degradation?

A
  • Monoamine oxidase (MAO)

- Catecol-O-methyltransferase (COMT)

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16
Q

How do monoamine oxidases work?

A
  • Oxidatively deaminates substrate to for inactive aldehyde derivatives
  • These are further converted to glycol derivatives
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17
Q

What are the 2 forms of MAOs?

A

MAOA and MAOB

18
Q

What do the 2 forms of MAO degrade?

A

MAOA higher affinity for noradrenaline and serotonin

Dopamine metabolised by both types

19
Q

What do MAOs degrade dopamine to?

A

DOPAL

- this further degraded to DOPAC

20
Q

What do MAOs degrade noradrenlaine to?

A

DOPEGAL

- further degraded to DOPEG

21
Q

How do Catecol-O-methyltranferases work?

A

Transfrer a methyl group

22
Q

What do COMTs degrade dopamine to?

A

3-Methyoxytyramine

23
Q

What do COMTs degrade Noradrenaline to?

A

Normetanephrine

24
Q

What occurs to the synthesis pathway in dopaminergic neurons?

A

Pathway terminates at DOPA decarboxylase and dopamine is packed into vesicles

25
Q

Where are catecholamines degraded?

A

In the pre-synaptic nerve terminal

- requires reuptake

26
Q

What are the 3 types of amino acid neurotrasmitters?

A

Glutamate
Gamma-aminobutyric acid (GABA
Glycine

27
Q

How do amino acid neurotramsitters differ from catecholamines?

A
  • Derived from glucose metabolism

- Taken up by glial cells as well as neurons

28
Q

What are the 2 sources of glutamate in glutamate and gaba neurons?

A

1) Derived from the citric acid cycle
- alpha-ketoglutarate converted to glutamate by GABA-transaminase (GABA-T) in mitochondria

2) From glutamate reuptake
- Glutamate taken from cleft into glial cell
- Converted to glutamine by glutamine synthetase
- Glutamine transported to neuron
- Converted back to glutamate by glutaminase
- Can also be taken fro the cleft straight back into neurons

29
Q

What happens to the glutamate in the pre-synaptic terminal?

A

Packaged into vesicles for regulated exocytosis

30
Q

What occurs to the glutamate in GABAergic neurons?

A

Converted to GABA by glutamic acid decarboxylase (GAD)

31
Q

What happens to the GABA after signalling?

A

Reuptake

  • converted to succinic semialdehyde by GABA-T
  • Succinic semialdehyde converted to succinate by succinic semialdehyde dehydrogenase which can rejoin the citric acid cycle
32
Q

How do the 4 enzymes described work?

A

1) GABA-transaminase
- catalyses exhange of NH2 and =O groups between amino acid and keto acid

2) Glutamine synthetase
- aminates glutamate in an ATP dependent manner

3) Glutaminase
- deaminates glutamine to glutamate using water

4) Glutamic acid decarboxylase
- decarboxylates glutamate to GABA

33
Q

Name some disorders that are a result of defective GABA/glutamate metabolism

A
  • Epilepsy
  • Cerebral palsy
  • Obesessive-compulsive disorders
  • Sleep disturbances
  • Brain malformations and many more
34
Q

How many (approx) peptide neurotransmitters are there?

A

At least 50 (more than classical transmitters!!!!)

35
Q

Give some examples of peptide neurotransmitters and their functions

A

1) Substance P - pain perception
2) Opioids (endorphins etc) - analgesic effects
3) Neuropeptide Y - feeding behaviour, circadian rhythm, anti-depression effects
4) Oxytocin - social behaviours, fear and anxiety
- Somatostatin - locomotor and cognitive behaviour

36
Q

What is the length of neuropeptide amino acid sequences?

A

Between 3 and 40 AAs

37
Q

What is the life cycle of peptide transmitters?

A

1) Peptide synthesis in the cell body (transcription and translation)
2) Vesicle (large dense core) packaging and axon transport
3) Ca2+ dependent exocytosis
4) Receptor (G-protein coupled) binding

5) Inactivation:
- enzymatic (zinc-metalloproteases)
- Autoreceptor internalisation
- Diffusion

38
Q

What is Dales Principle?

A

That a neuron is a single cell so all processes of the neuron may release the same neurotrasmitter

Interpreted to mean that a single neuron has 1 transmitter

39
Q

What observation proves Dales Principle wrong?

A

A single neuron may have more than one neurotransmitter

For example, many neurons use classical and peptide transmitters (co-localisation)

40
Q

What are the 3 advantages of co-localisation of neurotransmitters?

A

1) Different transmitter release to different stimuli
- e.g classical transmitters released at low frequency stimulation
- higher frequency stimulation leads to classic and peptide release

2) Modulation of signalling at single synapse
- co-released transmitters may modulate each other

3) Spatially restricting signalling
- different processes of presynaptic neuron may contain different neurotransmitters

3rd Year Biomed (44 decks)

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