Chapt. 4 - Stabilizing LTP

Question 1

What two central ideas guide memory research

Answer 1

1. memory trace evolves in stages
2. during the initial stages of memory, trace is vulnerable to disruption or improvement, and becomes less fragile with time.

Question 2

Delivery of low frequency stimulus immediately after TBS effects LTP how

Answer 2

prevents development of lasting LTP, immediately decreases and goes away

Question 3

Delivery of low frequency stimulus 10 minutes after TBS stimulation effects LTP how

Answer 3

does not prevent emergence of durable and lasting LTP

Question 4

What indications can be made from the different times of the delivery of low frequency stimuli and the effects it has to LTP

Answer 4

indicate synaptic changes that support LTP initially are not stable, and then 10 minutes later there are additional processes that work to stabilize LTP and decrease their vulnerability to disruption

Question 5

What is most likely the cause of LTP returning to baseline

Answer 5

the result of removal of AMPA receptors from the PSD (due to trafficking of AMPA receptors)

Question 6

___ processes want to remove recently added AMPA receptors from the PSD and return to baseline

Answer 6

Endocytotic (area/processing of recycling the receptors)
this pressures the synapses to want to get back to baseline

Question 7

because of endocytotic processes wanting to remove AMPA receptors, if potentiated synapses are going to endure longer than 30 mins , additional processes must create a ______ that will do two things

Answer 7

dendritic spine environment
1. limit depotentiating effects of endocytotic processes
2. ensure delivery of relevant synaptic proteins to maintain the new environment, useful proteins present! (AMPA receptors, kinases, scaffolding proteins, etc.)

Question 8

What structural changes in dendritic spines support LTP

Answer 8

spines come in variety of shapes and sizes, but large spines are more stable and endure longer. spine size is highly correlated with number of AMPA receptors in the PSD. enlarged spines are critical for the stability of synapses that support LTP and memory

Question 9

actin filaments help form the ____

Answer 9

spine cytoskeleton

Question 10

What two states does actin exist in

Answer 10

1. monomer state, G-actin (smallest building block)
2. polymer, F-actin

Question 11

treadmill actin

Answer 11

actin is in a continuous state of turnover, similar to treadmill, old units removed and new units added

Question 12

The state of ___ regulates actin polymerization. How?

Answer 12

cofilin (it is the main driver of size and strength of synapse)
in normal unphosphorylated state, it depolymerizes actin filaments.
when phosphorylated, LIMK cofilin (pCofilin) no longer interferes with actin polymerization

Question 13

When latrunculin and cytochalasin, prevent actin polymerization, are applied before TBS what happens to LTP

Answer 13

do not inhibit generation of LTP, but it rapidly decays

Question 14

When latrunculin and cytochalasin, prevent actin polymerization, are applied 15 mins after LTP is induced what happens

Answer 14

LTP is maintained and therefore proves polymerization is necessary to stabilize LTP

Question 15

Explain the stages in which enlarging and stabilizing actin cytoskeleton occurs

Answer 15

before inducing LTP, f-actin is connected and strands of active f-actin are bundled by inactive CaMKII complexes –> LTP inducing stimulus opens NMDA receptors –> influx of calcium –> Ca binds to calmodulin and activates CaMKII –> CaMKII disengages with the actin filaments and unbundles them –> unbundled filaments are exposed to severing (cutting/dividing) proteins like cofilin –> results in multiple strands of small actin filaments –> cofilin is phosphorylated which allows rapid polymerization of strands of actin which promotes expansions of the spine–> additional synaptic proteins reorganize actin into a stable framework

Question 16

Photocaging experiments

Answer 16

photocaging is a light triggered molecular tool.
CDNI-GLu is more effective is a way to cage glutamate
add structures to glutamate and that is what “cages them” and then photocaging/photostimulation to release glutamate when they want to see effects.

Question 17

In photocaging experiments, what was used to image and see what was occuring

Answer 17

inject the neuron with a vector of green florescent protein (GFP) to expose fluorescents when exposed to light to see tight and specifics of a particular spine

Question 18

photon uncaging of glutamate experiment results in what 3 findings

Answer 18

1. photon uncaging of glutamate over a single spine rapidly initiates the expansion of actin cytoskeleton
2. Inhibiting NMDA receptors by APV prevents expansions of spine
3. actin polymerization inhibitor latrunculin does not block initial expansion but prevents the expansion from lasting/enduring

Question 19

Explain the rapid turnover of actin-related proteins following the uncaging of glutamate

Answer 19

in the initial 5 mins, actin stabilizing proteins leave the spine while actin severing, branching, and capping proteins invade the spine
in the 7-60th minutes, gradual return happens for the actin stabilizing proteins

Question 20

What does myosin IIb do to actin filaments

Answer 20

is a motor protein that exerts a shearing action that breaks actin filaments into smaller units that can be reassembled anywhere in the spine

Question 21

applying drugs that inhibit myosin IIb prior to TBS and 10 minutes after induction cause what effects to LTP

Answer 21

before - prevents stabilization of LTP, and decrease
10 mins after - does not reverse LTP

Question 22

Ca enters through NMDA and activates two signaling cascades that regulate actin, explain each

Answer 22

Rho-Rock and Rac-Pak cascades.
BOTH activate LMK (kinase that phosphorylates cofilin and allows for actin polymerization)
Rac-Pak can also activate processes that reorganize and crosslink actin filaments to make them resistant to depolymerization

Question 23

Stabilization requires calcium-dependent cascades that activate ____ molecules. What are the two important classes of these molecules

Answer 23

cell adhesion
1. integrin receptors
2. neural cadherins

Question 24

What do integrin receptors do

Answer 24

they connect the extracellular space between the pre and postsynaptic sites to the cytoskeleton. Ca enters spine, influx –> increase Ca levels traffic integrin receptors in PSD and bind to ligands in extracellular matrix –> result of activation of the integrin receptors, actin filaments are organized to increase resistance to depolymerization

Question 25

Integrins are necessary to ___ LTP, but not to ____ LTP

Answer 25

stabilize
generate

Question 26

What do neural cadherins do

Answer 26

cadherin monomers weakly bonded the pre and postsynaptic –> higher frequency stimulation is delivered to induce LTP –> this stimulus promotes cadherin dimerization so the now enlarged spine containing AMPA receptors, is pulled closer to the presynaptic terminal and receive glutamate released from the presynaptic terminal

Question 27

_____ of LTP requires N-cadherins

Answer 27

stabilization

Question 28

Experiment to show that stabilization of LTP requires N-cadherins

Answer 28

spines activated by TBS and become larger and contain N-cadherins
TBS induces LTP in slices of mice that have genetically no gene for N-cadherins and therefore cannot sustain LTP

Question 29

LTP is stabilized in 3 overlapping stages: (and requires one more thing…)

Answer 29

1. Actin severing events are engaged
2. GTPase signaling leads to phosphorylated cofilin and rapid polymerization of actin and a large stable of F-actin
3. actin stabilizing proteins rebundle actin filaments, crosslink them, and bind them to plasma membrane
   also requires recruitment of integrin to strengthen filaments and reorganization of N-cadherins to increase proximity of pre and post site