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PHAR2005 > Amino Acid Neurotransmitters > Flashcards

Amino Acid Neurotransmitters Flashcards

1
Q

What are the main AA NTs ?

A
  • Glutamate
  • GABA (γ-aminobutyric acid)
  • Glycine
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2
Q

What are the steps of synaptic transmission ?

A
  1. Uptake of precursors
  2. Synthesis of transmitter
  3. Uptake into vesicles
  4. Metabolism of transmitter
  5. Invasion of action potential
  6. Ca2+ influx
  7. Exocytosis of vesicles
  8. Diffusion to receptors
  9. Action at postsynaptic receptors
  10. Diffusion away from synapse
  11. Re-uptake by neuron
  12. Re-uptake by glia
  13. Action on presynaptic receptors
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3
Q

What are the main characteristics of Glu ?
How is it taken up from the extracellular space ?
How is it concentrated in vesicles ?

A
  • Most widespread excitatory neurotransmitter in the CNS
  • Taken up from the extracellular space by specific transporters - Excitatory Amino Acid Transporters (EAAT1-5)
  • Concentrated in vesicles in glutamatergic neurons, but not in others - Vesicular Glutamate Transporter (VGLUT)
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4
Q

How is Glu synthesized and metabolized ?

A

alpha-ketoglutarate (from TCA cycle) –> Glu (via Glu dehydrogenase) + part of the Glu converted to gluthione, polyamines, urea, GABA
Glu –> Gln (via Glu synthetase (glutaminase for Gln –> Glu) + part of the Gln conerted to amino sugars, glucoproteins, nucleotides

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5
Q

What are the main characteristics of GABA ?
How is it taken up from the extracellular space ?
How is it concentrated in vesicles ?

A
  • Most widespread inhibitory neurotransmitter in the CNS
  • Synthesized from glutamate via cytosolic enzyme - Glutamic Acid Decarboxylase (GAD)
  • Taken up from the extracellular space by specific transporters - GABA Transporters (GAT1-4)
  • Concentrated in vesicles in GABAergic neurons, but not in others - Vesicular Inhibitory Amino Acid Transporter (VIAAT)
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6
Q

What are the main characteristics of Gly ?
How is it taken up from the extracellular space ?
How is it concentrated in vesicles ?

A
  • Inhibitory neurotransmitter in mammalian spinal cord
  • Simplest amino acid; derived from metabolism and synthesized in all cells
  • Taken up from the extracellular space by specific transporters - Glycine Transporters (GlyT-1 and GlyT-2)
  • Concentrated in vesicles in glycinergic neurons - VIAAT (note, some neurons can release both GABA and Glycine)
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7
Q

What different types of GluRs exist ?

A

Glutamate receptors : ionotropic Vs metabotropic
Ionotropic : NMDA Vs non-NMDA
Metabotropic : mGluRs
non-NMDA : AMPA Vs kainate

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8
Q

How do ionotropic Vs matebotropic GluRs differ ?

A

iGluR subunit : 4 membrane domains (M1 to M4)

mGluR subunit : 7 transmembrane domain (M1 to M7)

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9
Q

What are the three classes of iGluR ?

A
  • N-methyl-D-aspartate (NMDA)
  • α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)
  • Kainate
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10
Q

Name 4 iGluR agonists.

A

L-Glutamate, NMDA, Kainate, AMPA

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11
Q

What genes are part of the AMPA, kainate and NMDA family ?

What are agonists and co-agonists for these receptors ?

A

AMPA : GluA1, GluA2, GluA3, GluA4 (Glu, AMPA, Kainate)
Kainate : GluK1, GluK2, GluR3, GluK4, GluK5 (Glu, Kainate, Domoic Acid)
NMDA : GluN1, GluN2A, GluN2B, Glu2C, GluN2D, GluN3A, GluN3B (Glu, Gly, NMDA)

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12
Q

Do Glu gated ion channels assemble as :

  • trimers ?
  • tetramers ?
  • pentamers ?
A

Tetramers.

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13
Q

How are mGluR sub-types grouped ?

A

Group I : mGlu1 + mGlu5 => +PLC (IP3)
Group II : mGlu2-3 => -AC (cAMP)
Group III : mGlu4 + mGlu6-8 -AC (cAMP)

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14
Q

How do AMPA/KainateRs VS NMDARs Vs mGluR work ?

What are agonists (endogenous and exogenous) and antagonists at these receptors ?

A

AMPA/Kainate : work by Na+/K+ influx, activate by Glu and exogenously by AMPA/Kainate, inhibited by CNQX
NMDA : work by Na+/K+/Ca2+ influx, activated Glu/Gly and exogenously by NMDA, inhibited by AP5 and 7-CK
mGluR : work via 2nd messengers (IP3, cAMP), activate by Glu and exogenously by ACPD, inhibited by various compounds

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15
Q

What are the two types of integration that can occur in neurons ?

A

Spatial and temporal.

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16
Q

What is the special feature of NMDARs ?

A

The ion channel is normally blocked by a Mg2+ ion.

Relief of Mg block leads to further depolarization and Ca2+ entry.

17
Q

Glu is taken up into vesicles in exchange fo H+. How is the proton concentration maintained in the vesicle ?

A

Via a proton transporter (an ATPase : ATP –> ADP + Pi)

18
Q

What are the 2 classes of GABA receptors ?

A 
Ionotropic : GABA(A) and sometimes GABA(C)...
Metabotropic GABA(B)
19
Q

How do the different GABARs work ?

What molecules are agonists/antagonists at these receptors ?

A 
GABA(A) = increases Cl- influx, activated by GABA and exogenously by muscimol, inhibited by bicuculiline
GABA(B) = increase K+ efflux and decrease Ca2+ influx (Gi/o, cAMP), activated by GABA and exogenously by baclofen, inhibited by CGP 35348
20
Q

What is another name for the cys-loop receptor family ?
What are the characteristics of receptors belonging to this family ?
Give examples of receptors.

A 
Cys-loop receptor superfamily = nACh superfamily
All pentameric : 
nACh receptors
5-HT(3) receptors
GABA(A) rceptors
Glycine receptors
21
Q

What are the members of the Glu receptor family ?

What is their common feature ?

A

All tetramers :
NMDA receptors
AMPA receptors
Kainate receptors

22
Q

How many GABA(A) subunits do we currently know ?

A 
6 alpha
3 beta
3 gamma
1 delta
1 epsilon
1 pi
1 theta
2 rho
23
Q

Name 4 GABA(B) agonists and 3 antagonists.

A 
Agonists : 
- GABA
-  APPA
- (R)-baclofen
- Gabapentin
Antagonists : 
- (R)-phaclofen
- CGP 54626
- CGP 64213
24
Q

What is the effect of 2-OH-saclofen on GABAergic transmission ?

A

In prevents the late IPSP in the postsynaptic cell from occurring.

25
Q

How is GABA metabolized ?

A

In the mitochondria (of neurons or glial cells) :
GABA –> Succinic semialdehyde (SSA) via GABA-T
SSA –> Succinate via SSA dehydrogenase (SSADH)

26
Q

Name 6 molecules or classes of molecules that are modulators of GABA.

A
  • benzodiazepines
  • barbiturates
  • steroids
  • intravenous anaesthetics
  • inhalation anaesthetics
  • alcohol
27
Q

What is diazepam ?

What is it used for ?

A

Diazepam is an BDZ.
It is an anxiolytic, sedative, muscle relaxant anti-convulsant and attenuates autonomic endocrine response.
It is used to treat :
- acute anxiety
- insomnia
- epilepsy
It is also used as pre-medication during surgery, and as a sedative during minor medical procedures.

28
Q

What did Leo Sternbach (1908-2005) synthesize in the 1950s-1960s ?
How did this have an impact ?

A

Synthesized :
- chlordiazepoxide in 1955 –> marketed by Roche as Librium (1960)
- diazepam in 1959 –> marketed as Valium (1963)
Between 1969 and 1982 Valium was the most prescribed drug in the world.

29
Q

What do the effects of BDZ depend on ?

A

Effects of BDZ correlate with binding.

30
Q

How do BDZs affects the dose-response curve ?

A

BDZs are positive allosteric modulators (cause a parallel shift in the dose-response curve to the left).

PHAR2005 (24 decks)

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