exam 1 Lecture 2

Question 1

What ions do AMPARs pass?

Answer 1

Na+, K+ and Ca2+

Question 2

Why are NMDARs important to LTP and how do you activate them?

Answer 2

NMDARs are the key contributors to LTP because they let in calcium, which is required for sustaining the response of LTP.

1. At resting membrane potential, the electrochemical gradient pulls in Mg2+ into the cell.
2. If the spine is sufficiently depolarized, the pull on the Mg2+ ion weakens and it leaves, unblocking the NMDAR.
3. The NMDAR is now able to let in Ca2+.

Question 3

How did researchers determine the three levels of LTP and what are the three levels, and how long do they last for?

Answer 3

They determined it through whole cell patch recording and recorded the EPSP percent change from the baseline.
LTP1- minutes-hours
LTP2-days-weeks
LTP2-weeks-months

Question 4

What are the receptors associated with each LTP?

Answer 4

LTP1-ryanodine receptor
LTP2-IP3 receptor
LTP3-L-VDCC

Question 5

How do you know that LTP2 does not depend on LTP1 and LTP3 does not depend on LTP2?

Answer 5

The researchers blocked IP3 channels, which blocked LTP2 but had no affect on ryanodine receptors and L-VDCC receptors. They blocked L-VDCC receptors which blocked LTP3 but LTP1 and LTP2 remained unaffected.

Question 6

How do you know if the calcium channel blockers worked? What study did they do?

Answer 6

They studied the cytosolic calcium levels using fluorescent calcium dyes. They then measured the change in fluorescence and divided by the baseline fluorescence. They added blockers. If the calcium channel blockers worked then LTP decreases.

Question 7

Why was the fluorescence for the dendrite brighter than the fluorescence for the spine, but the values of the spine greater than the dendrite on the graph?

Answer 7

The baseline fluorescence for the spine was less than the baseline fluorescence for the dendrite.

Question 8

How do you initiate LTP2?

Answer 8

Look at diagram in notes.

Question 9

How do you initiate LTP1?

Answer 9

Look at diagram in notes.

Question 10

Why did researchers initially believe that GluA1 is required and S831 is phosphorylated in LTP?

Answer 10

S381 is part of the GluA1 subunit. They removed GluA1 which interfered with LTP1, but removing GluA2 and GluA3 had no effect on LTP1. Then, they mutated the S831 to S831A and found that LTP1 decreased.

Question 11

NMDARs ____LTP and AMPARs____LTP

Answer 11

start

sustain

Question 12

How does AMPAR conductance increase during LTP?

Answer 12

Original AMPARs get replaced by CP AMPARs so the inward current increases due to increase in AMPARs.

Question 13

Walk through rectification

Answer 13

GluA1. AMPARs with GluA2 are not permeable to calcium because they have an arginine, which is positively charged. The arginine replaces the spermine so the inward and outward current are equal, leading to very little rectification. When the GluA2 containing AMPARs get replaced with the GluA1 containing AMPARs, they have a glutamine in place of arginine, which has no charge. Therefore it does not replace spermine, and only inward current is possible. Therefore inward current increases leading to rectification.

Question 14

Describe whole cell patch recording

Answer 14

1. Put the pipette against the cell surface.
2. the inside of the membrane becomes continuous with the pipette
3. clamp the current wherever you want.

Question 15

What happens in LTP induction?

Answer 15

1. calcium flows in through NMDARs
2. This stimulates the ryanodine receptors to release more calcium.
3. the non GluA2 CP AMPARs replace the GluA2 CIP AMPARs.
4. CP AMPARs let in calcium.
5. CP AMPARs get replaced by edited GluA2 containing CIP AMPARs to stabilize the LTP.

Question 16

Describe post tetanic activity in LTP.

Answer 16

The researchers gave baseline cells a TBP. They added kineuric acid, which block NMDA receptors. The baseline decreases. After removing kineuric acid the baseline increases normally to how it should be without the kineuric acid. Therefore, the insertion of CP AMPARs still continues even if you blocked the NMDARs.

The researchers concluded that the CP AMPARs are present in LTP. They treated the cells with PhTx433 which reduced the EPSP slope. This means that the drug blocks the insertion of CP AMPARs, blocking LTP. Then they added the drug 30 minutes after, which reduced LTP, then 50 minutes after which didn’t change anything. This shows that all the AMPARS are calcium impermeable so that doesn’t affect LTP. They then added the drug continuously, which fully blocks LTP. This shows that the new receptors are phosphorylated and the new receptors are calcium permeable.