Synaptic Transmission II

Question 1

Glutamate receptors are…

Answer 1

• ion channels
• They are permeable to cations (positively charged ions) including Na+ and K+

Question 2

The point at which there is no current…

Answer 2

• is the reversal potential Erev
• The reversal potential for glutamate receptors is 0mV. When the cell’s membrane potential is 0mV, no current will flow through these channels.

Question 3

GABA

Answer 3

• a neurotransmitter that binds to GABA receptors which are ion channerls permeable to only chloride.
• Erev is -65mV

Question 4

By voltage-clamping the membrane and measuring how much current flows into or
out of the neuron in the presence of a neurotransmitter…

Answer 4

• you can determine which ions flow through the postsynaptic receptor.

Question 5

Each EPSP or IPSP produced by binding of a neurotransmitter to areceptor may be only a fraction of a millivolt. How do synaptic responses ever reach threshold?

Answer 5

• Neurons typically have thousands of synapses. The EPSPs and IPSPs produced at each synapse sum together.

Question 6

Two types of summation:

Answer 6

• spatial and temporal.

Question 7

Spatial summation:

Answer 7

• adding together of PSPs generated simultaneously in different parts of the dendrite.

Question 8

Temporal summation:

Answer 8

• adding together of PSPs generated at the same synapse if they occur in rapid succession (within about 1-15ms of one another)

Question 9

To reach the axon hillock, the current…

Answer 9

• passively propagates through the cell.
• the current decays

Question 10

Passive current flow:

Answer 10

• Conduction by neurons in the absence of action potentials.
• It is like conduction of electricity in a wire.

Question 11

Synaptic potentials close to the cell body
will still be large when they reach the cell
body. (Proximal)

But,

Answer 11

• synaptic potentials generated further
  away will be much smaller because they
  have to passively propagate over a long
  distance. (Distal)
• the closer potential has a greater chance of producing an action potential.

Question 12

Neurotransmitters and their receptors

Answer 12

• Glutamate: AMPA receptor
• GABA: GABA receptor
• Acetylcholine: nicotinic acetylcholine receptor

Question 13

Glutamate:

Answer 13

• the major excitatory neurotransmitter in the brain nearly all excitatory cells in the CNS are glutamatergic over ½ of all brain synapses are glutamatergic

Question 14

Glutamine, Glutamate, VGLUT, EAATs

Answer 14

• presursor to glutamate
• x
• transports glutamate into the vesicles
• After NT is released and bound to receptors, EAAT transports the recycled glutamate away from synapse.

Question 15

There are three types of ionotropic glutamate receptors:

Answer 15

• AMPA, NMDA and kainate
• All are non-selective cation channels, permeable to Na+ and K+.

Question 16

Structure of the AMPA receptor:

Answer 16

• Composed of 4 subunits
• Glutamate binds to the ligand-binding domain
• C-terminal domain can interact with proteins in the cytoplasm
• Binding of glutamate to 2 of the 4 subunits closes the “clamshell” structure and
  opens the pore.
• Current increases as more binding sites are occupied

Question 18

The AMPA receptor:

Answer 18

• Permeable to Na+ and K+
• Reversal potential = 0 mV
• Binding of glutamate to the AMPA receptor causes a NET inward positive
  current and a depolarization of the membrane. (EPSP)

Question 19

GABA is a neurotransmitter that binds to…

Answer 19

• ## GABA receptors which are ion channels permeable only to chloride

Question 20

The GABAA receptor: an ionotropic receptor

Benzodiazepines

Answer 20

• Benzodiazepines: anxiety-reducing drugs
  Example: diazepam (Valium)
• They enhance GABA transmission by
  binding to the alpha and delta subunits of the GABAA receptor.
• When GABA is present, benzodiazepines
  increase the frequency of channel openings.
  End result?
• more chloride conductance

Question 21

The GABAA receptor: an ionotropic receptor

Barbituates

Answer 21

• Barbituates: sedatives and anticonvulsants
  Example: phenobarbital
• They enhance GABA transmission by
  binding to the  and  subunits of the
  GABAA receptor.
• When GABA is present, barbituates
  increase the duration of channel
  openings.
  End result?
• More chloride conductance

Question 22

Excitatory actions of GABA in the developing brain

Answer 22

• in an immature neuron, GABA causes an excitatory effect instead of an inhibitory effect. (intracellular region becomes more +)