long term potentiation (LTP)

Introduction

LTP is an activity-dependent synapse-specific increase in synaptic efficacy. It is long-lasting, persisting for days to weeks.

LTP is a form of neuronal plasticity that may form the basis for associative learning. It has been demonstrated in 3 major excitatory pathways in the hippocampus:

• the perforant pathway
• mossy fiber pathway
• Schaeffer collaterals

LTP occurs when a brief high frequency train of stimuli is applied to any of the 3 pathways above. The result is an increase in excitatory postsynaptic potential which may last days to weeks.

LTP has 3 important properties:

• cooperativity (more than 1 fiber must be activated to facilitate LTP)
• associativity* (Hebb's rule: LTP requires depolarization of the postsynaptic neuron coincident with activity of the presynaptic pathway)
• specificity (LTP is specific to the active pathway)

* LTP of the mossy fiber pathway may not be associative

Ca+2 influx through NMDA receptors is critical for induction of LTP; it is also necessary for LTP decay. Phosphorylation/dephosphorylation at GluR1 of AMPA receptors may also play a role.

In contast to LTD, high levels of intracellular Ca+2 are required for LTP.

The voltage-gated K+ channels, K+ A channel & K+ D channel may participate in LTP through inhibition or termination of Ca+ influx.

More general terms

• facilitation (enhancement)

Additional terms

• associative memory/learning (conditioning)
• hippocampal mossy fiber pathway
• learning
• NMDA receptor
• perforant pathway
• Schaeffer collaterals