Lec8: Long-Term Potentiation

Question 1

What are the 3 phases of LTP? Draw a diagram.

Answer 1

1. Induction - Stimulation of presynapses to increase synaptic strength
2. Expression - HOW MUCH synaptic strength increases
3. Maintenance - HOW LONG increased synaptic strength is maintained `

Question 2

Who discovered LTP and in what year? In what part of the brain did they search for increased synpatic strength and what was their final discovery?

Answer 2

Bliss and Lomo, 1973.
Searched in the Dentate Gyrus (1st cortical pathway entering the hiipocampus), and found that synaptic strength remained elevated even after 14 hours. This was described as “a timescale long enough for potentially useful information storage.”

Question 3

What are the three properties of LTP and describe each?

Answer 3

1. Input specificity = only stimulated synapses are potentiated
2. Saturable = max synaptic strength exists
3. Cooperativity/Associativity = Requires BOTH presynaptic and posrsynaptic depolarisation to generate LTP.

Question 4

What are the three methods that LTP is induced in the lab?

Answer 4

1. Tetanic stimulation = brief bursts of high frequency (100Hz) stimulation of axons and presynapses, causing huge glutamate release and therefore huge AMPAR activation and postsynaptic depolarisation.
2. Pairing = low frequency stimulation of presynapses combined with postsynaptic depolarisation.
3. Theta burst stimulation = presynapses stimulated using a frequency of 6-10Hz

Question 5

In the process of “Pairing”, how is the postsynaptic terminal depolarised?

Answer 5

Artificially induced depolarisation. Current is injected into the postsynaptic cell.

Question 6

What is the purpose of Ca2+ influx in terms of LTP induction?

Answer 6

Activates Calcium calmodulin dependent kinase 2 (CAMKII) which phosphorylates AMPAR.

Question 7

How does CAMKII increase synaptic transmission to generate LTP?

Answer 7

CAMKII phosphorylates:

1. New AMPAR = insertion of additional AMPAR into postsynaptic membrane
2. Existing AMPAR = Increase conductance (modified to bring in more Na+)