Ch 8 - Synaptic Plasticity (pt 2)

What structure is studies a lot in terms of SP

Hippocampus

What is the hippo known for?

Formation of declarative memories

How are glutamatergic (excitatory) neurons In hippocampus connected?

In a trisynaptic circuit

Where is LTP (Long-term potentiation) found?

Synapses throughout the trisynaptic circuit

Where is the best form of LTP?

Schaffer collateral synapses

What are the properties of LTP?

• LTP can last for a year

• Long duration show LTP can serve as a mechanism for long-term information storage

What is another property of LTP?

Specificity

• When LTP indices at one synapse, it doesn't occur in another. No change unless at one where induced. Connected to memory formation

What is a 3rd property of LTP

Associativity

• When weak stimulus does not result in LTP, when paired with strong stimulus it results to experience LTP

  • Associative learning

What two ways can LTP be experimentally induced at Schaffer collateral synapses?
What is the Donals Hebb theory

1. Repetitive stimulation of presyn. afferent at high frequencies

2. Pairing presynaptic stimulation with postsynaptic depolarization only if tightly linked in time.

   • Donals Hebb theory: coincident activity → strengthening of synaptic connections

How do NMDARs serve as coincidence detectors?

• No effect on synaptic response during low-frequency stimulation due to Mg²⁺ block of channel pore

• Mg²⁺ expelled upon coincident glutamate binding and postsynaptic membrane depolarization: Influx of Ca 2+, calcium signalling

What does Ca2+ influx through NMDArs activate?

Calcium/calmodulin-dependent kinase II (CaMKII)

CaMKII:

• Required for LTP

• Signaling restricted to synapse
  undergoing LTP

• Persistent activation following LTP
  through autophosphorylation

What leads to an increase in responsiveness to glutamate?

LTP at Schaffer collaterals and many other glutamatergic synapses

What are mechanisms that lead to ncreases in glutamate responsiveness at synapses undergoing LTP?

1. Insertion of AMPA-type glutamate receptors (AMPARs) into postsynaptic membranes

2. Post-translational modifications such as phosphorylation leading to an increase in conductance of individual AMPAR channels.

What other mechanism may contribute to LTP expression?

1. Increases in the size of spines and synaptic appositions of potentiated synapses

2. New synapses

3. Increases in presynaptic probability of glutamate release

4. Protein syntesis