synaptic plasticity

Question 1

induction of LTD at CA3-CA1 synapse

Answer 1

NMDA receptor-dependent LTD
depenedent on activation of phosphatases
can be saturated and reversed
different LTD mechanism exist (mGluRs, VGCC, KARs)

Question 2

expression of LTD at CA3-CA1 synapse

Answer 2

synaptic silecing may be a way of pruning syanpses during development

Question 3

long-term depression

Answer 3

low frequency stimulation (LFS)
induces LTD at CA3-CA1 synapses
typical LFS used to induce LTD –900 stimuli delivered at 1 Hz (1 per second)
LTD is input specifi

Question 4

frequency depenedent and NMDA LTP and LTD

Answer 4

deliver 900 pulses at a
range of frequencies
low frequencies = LTD
as frequency increases
magnitude of LTD
decreases
high frequencies = LTP

Question 5

how can LTP and LTD both be dependent on NMDA receptor activation?

Answer 5

the size and time course of NMDA receptor activation and
calcium influx differ between LTP and LTD induction
LTP results from a large intracellular calcium rise for a short
period of time
LTD results from a smaller rise in calcium (over a longer time
scale)
enzymes (kinases/phosphatases) have different sensitivities to
calcium
kinases= excocytosis in AMPA

Question 6

what is hebb’s postulate?

Answer 6

neurons that fire together, wire together

Question 7

LTP and hebbian plasticity

Answer 7

synapses are strengthened when both the postsynaptic and presynaptic cell are active during the induciton protocol
NMDA receptor acts as a coincident detector – needs postsynaptic
depolarisation and presynaptic release of glutamate

Question 8

LTD and anti-hebbian plasticity

Answer 8

synapses are weakened when both the presynaptic and postsynaptic cells are active during the induction protocol

Question 9

bidirectional modifiable synapses

Answer 9

theta burst stimulation
decrease in trenamission from potentiation (de-potentiation)
useful for models of learning and memory

Question 10

LTD in other brain regions

Answer 10

cerebellum- LTD occurs and is involved in motor learning
perihinial cortex- LTD occurs and is involved in object recognition (temporal lobe)

Question 11

cerebellar LTD

Answer 11

stimulate parallel fibres coupled with depolarisation
of purkinje cell produces LTD
this is anti-hebbian

Question 12

mechanisms of cerebellar LTD

Answer 12

requires activation
of both AMPA and
metabotropic
glutamate receptors
activation of protein
kinase C essential
AMPA receptors are
internalised, reducing number expressed at cell surface

Question 13

does LTD=learning in perihinal cortex?

Answer 13

record from perirhinal cortex neurones; measure action potential firing;
Present picture of a novel object, neurones increase AP firing;
Present same image again, response of neurone is much reduced; LTD-like effect?
-induced by LFS
-input specific
-dependent on NMDA receptor activation
-LTD can be blocked by
putting a peptide into the postsynaptic cell that interferes with removal of AMPA receptors from the
cell surface

Question 14

LTD in perihinal cortex of animals

Answer 14

using a virus to express same peptide in perirhinal cortex of animals blocks recognition memory
rats allowed to explore a novel and a familiar object. they will spend more time exploring the novel object. discrimination ratio is a measure of this – a ratio of 0 means the rat spends equal time
exploring the two objects
so peptide that blocks LTD in vitro also blocks learning in vivo