Initiation of functional synapses is associated with AMPA receptor expression

In the present study, we identified the key protein that modulates the initiation of functional glutamatergic synapses in developing cortical neurons. First, we found a day in vitro that marked a critical increase in the number of functional synapses by the application of cyclic AMP, as demonstrated with Ca²⁺ imaging. We then examined the changes in the expression levels of proteins, which were expected to play a role in glutamatergic synapses, by the application of cyclic AMP. Our findings suggest that the expression of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors modulates the initiation of functional synapses in developing neurons, and that immature neurons already contain N-methyl D-aspartate (NMDA) receptors and presynaptic proteins such as synaptophysin.