Plasticity and learning

Question 1

Mechanisms Underlying Long-Term Potentiation

Answer 1

• NMDA receptor channel is permeable to Ca2+ but is blocked by Mg2+ at the normal resting membrane potential
  • NMDA receptor is a molecular coincidence detector:
    The channel of this receptor opens (toinduce LTP) only when glutamate is bound to the receptor,
    and the postsynaptic cell is depolarized to relieve the Mg2+ block of the channel pore.
  • During high-frequency stimulation, Removal of Mg2+ then allows Ca2+ to enter the
    dendritic spines of postsynaptic CA1 neurons

Question 2

Mechanisms Underlying Long-Term Depression

Answer 2

LTD occurs when the Schaffer collaterals are stimulated at a low rate—about 1 Hz—for long periods (10–15 minutes).

- Mechanisms underlying LTD. A low-amplitude rise in Ca2+ concentration in the postsynaptic CA1 neuron activates postsynaptic protein phosphatases, which cause internalization of postsynaptic AMPA receptors, thereby decreasing the sensitivity to glutamate released from the Schaffer collateral terminals.