Glutamatergic neurotransmission

Question 1

Glutamate

Answer 1

• mediates fast excitatory neurotransmission in CNS
• mediator of sensory information, motor co-ordination, emotion and cognitions
• penetrates blood-brain barrier poorly

Question 2

1. Glutamate dehydrogenase

Answer 2

• present in mitochondria
• Glu -> alphaKG + NH3
• low affinity to ammonia, Km=1mM
• NAD+/NADP+ as cofactor
• allosteric inhibitor: ATP, GTP
• allosteric activator: ADP, GDP

Question 3

2. Transaminases

Answer 3

ALAT:
- transfer of amino group from alanine to alpha KG
- product: pyruvate + Glu
- requires PLP
ASAT:
- Asp + alphaKG -> OAA + Glu
- requires PLP

Question 4

3. Glutamine synthetase

Answer 4

• glutamate -> glutamine in astrocytes

- glutamine supplied to presynaptic terminals

Question 5

4. Glutaminases

Answer 5

• in axonal terminal in CNS
• phosphate-activated mitochondrial glutaminase
• glutamine + H2O -> glutamate + NH3

Question 6

EAAT 1/ EAAT 2

Answer 6

• reuptake of glutamate to presynaptic neuron or astrocyte
• co-transport of 3Na+ and 1H+ into cell
• counter transport of 1 K+
• works agains conc. gradient

Question 7

SN1/SN2

Answer 7

transport of glutamine out of astrocyte and into presynaptic neuron

Question 8

VGLUT 1/2

Answer 8

• glutamate uptake into vesicles
• proton gradient- H+ATPase
• stimulated by Cl-
• in glutamatergic neurons
• VGLUT3- in cholinergic, GABAergic and monoaminergic neurons

Question 9

Glutamate receptors

Answer 9

Ionotropic: NMDA, AMPA, Kainate
Metabotropic: class 1,2,3

Question 10

AMPA receptors

Answer 10

• ionotropic transmembrane receptor
• 4 sites to which agonist can bind, one for each subunit formed by N-tail + extracellular loop between transmembrane domains 3 and 4
• when agonist binds - 2 loops move towards each other - pore
• channel may undergo desensitization
• permeability to cations governed by GluR2 subunit

Question 11

Mechanism of AMPA receptor

Answer 11

ligand binding - pore open - Na+ influx - depol. - activation of AMPA - decreased inhibition of NMDA by Mg2+ - NMDA activation

CA2+ entry - phosphorylates CaMKII - phosphorylates AMPARs and Ras MAPK - more AMPARs translocate to membrane - long term potentiation - long term memory

Question 12

NMDA receptors

Answer 12

• heterometric receptors
• mRNAs encoding receptor subunits:
  
  • NR1: brain(glycin binding site)
  • NR2: CNS (glutamate binding site)
  • NR3: spinal cord
• Na+ and Ca2+ permeable channels
• 6 binding sites
• activators: glutamate and glycine, poliamines
• inhibitors: Mg2+, H+, Zn2+

Question 13

NMDA receptor activation

Answer 13

activation - Na+, Ca2+ permeability - Ca2+ influx - transient stimulation of Ca2+ dependent enzymes:

• Ca2+-CAM dependent protein kinas 2
• calcineurin
• PKC
• PLA2
• PLC
• NO synthetase
• endonucleases

Question 14

Metabotropic receptors

Answer 14

• G protein coupled
• 8 subunits
• mGluR- pre ans postsynaptic localisation
• linked to cytoplasmic signaling
• modulate: ion channels, receptors, presynaptic receptor inhibition

Question 15

Excitatory AA transporters, EAATs

Answer 15

• EAAT1: astrocytes
• EAAT2: in forebrain in astrocytes + nerve terminals
• EAAT3: neuronal
• EAAT4: dendrites of parking cells
• EAAT5: retina

Question 16

Na+ dependent transporters in axon terminal

Answer 16

1. GABA, glycine, NE, dopamine, serotonin transporters
2. Na+Cl- dependent transporters
3. Na+K+ dependent glutamate transporter
   
   • 3Na+, 1H+ in, 1K+ out - electrogenic
   • anoxia reversal
   • overexcitation - ischemia, epileptic seizures etc.