Memory  >   AMPA Receptors Determine Synaptic Strength

The synaptic strength is a measure of the connectivity between two neurons. More specifically, it indicates the firing probability of a postsynaptic neuron when a presynaptic neuron fires. As discussed in the previous chapter, neuronal firing depends on the summation of EPSPs and IPSPs that spread to the axon initial segment. A larger EPSP should facilitate neuronal firing.

Glutamate is the major neurotransmitter involved in memory. After being released from the axon terminal of the presynaptic neuron, it may bind to receptors located on the postsynaptic membrane. Both AMPA receptors (AMPARs) and NMDA receptors (NMDARs) may contribute to EPSPs. However, the opening of NMDARs requires not only glutamate binding, but also the relief of Mg2+ block. The latter is regulated by electric fields, independent of the presynaptic neuron. In contrast, the glutamate released from the presynaptic neuron is sufficient to activate AMPARs. Therefore, the number of synaptic AMPARs is a better determinant than NMDARs for the synaptic strength (Figure 3-1), as demonstrated experimentally (Granger et al., 2013; Sheng et al., 2013).


Figure 3-1. Synaptic strength is determined by the number of synaptic AMPARs. (A) has stronger synaptic strength than (B).


Author: Frank Lee
First Published: January, 2018