Synaptic Plasticity: LTP/LTD/Homeostatic Plasticity

Question 1

What is necessary for LTP/LTD to occur?

Answer 1

Ca2+ is required. Presynaptic and postsynaptic neurons must be paired so that depolarization removes the Mg2+ block from NMDA receptors. NMDA allows Ca2+ influx.

Question 2

Give synaptic parameters that govern EPSP size:

Answer 2

• number of vesicles in the presynaptic cell.
• Probability of vesicle release from presynaptic cell.
• Amplitude response of postsynaptic cell to contents of 1 vesicle.

Question 3

What is a silence synapse? How is a silent synapse unsilenced?

Answer 3

A silent synapse shows no postsynaptic voltage response to neurotransmitter released from the presynaptic terminal.

To unsilence a synapse Glu released from the presynaptic cell must bind to NMDA receptors on the post-synaptic cell. The post-synaptic cell must be depolarized (by other active synapses) so that spiking occurs. A backpropogating action potential depolarizes the synapses on the dendrites which removes Mg2+ blockade from the NMDA channels. Ca2+ entry into silent synapse causes AMPA receptor insertion into cell membrane. AMPA receptors unsilence the synapse.

Question 4

Define the principle of homeostatic plasticity:

Answer 4

Prevents runaway potentiation from occuring by reducing the synaptic efficacy of strong synapses. Application of TTX to the presynaptic terminal over time results in an increased “mini” size while application of bicuculline results in a decreased “mini” size.