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Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss long-term potentiation, or LTP.
LTP is a process by which synaptic connections between neurons become stronger with frequent
activation.
LTP is thought to be a way in which the brain changes in response to experience, and thus
may be an mechanism underlying learning and memory.
There are a number of ways in which LTP can occur.
The best-known mechanism involves a glutamate receptor known as the NMDA receptor.
In NMDA-receptor dependent LTP, glutamate release first activates a subtype of glutamate
receptor known as the AMPA receptor.
NMDA receptors are found nearby these AMPA receptors, but are not activated by low levels
of glutamate release because the ion channel of an NMDA receptor is blocked by a magnesium
ion.
If frequent action potentials cause greater stimulation of AMPA receptors, however, this
will cause the postsynaptic neuron to depolarize,
which eventually causes the voltage-dependent magnesium blockage of the NMDA receptor to
be removed, allowing calcium ions to flow in through the NMDA receptor.
This influx of calcium initiates cellular mechanisms that cause more AMPA receptors
to be inserted into the neuron’s membrane.
The new AMPA receptors are also more responsive to glutamate, and allow more positively charged
ions to enter the cell when activated.
Now, the postsynaptic cell is more sensitive to glutamate because it has more receptors
to respond to it.
Additionally, there are thought to be signals that travel back across the synapse to stimulate
greater levels of glutamate release.
All of this makes the synapse stronger and more likely to be activated in the future.
This process is also associated with changes in gene transcription in the neuron, which
can lead to the production of new receptors or modifications to the structure of the cell.
These changes seem to be important for making the increased responsiveness of LTP long-lasting.