Glutamate synapse in developing brain: an integrative perspective beyond the silent state.

Cellular events underlying the establishment of glutamate transmission have been the focus of attention because appropriate wiring of developing neuronal networks is essential for adult brain functions. Although establishment of a synapse is a dynamic process requiring axonal and dendritic refinements, the functional interplay between pre- and postsynaptic signaling is often ignored. Here, we discuss recent data on pre- and postsynaptic plasticity of the glutamate synapse in the developing brain. The key aspect of the proposed model is that developing synapses are functionally labile in response to activity and this lability is counteracted by Hebbian activity. Both presynaptic and postsynaptic (loss of AMPA receptor signaling) mechanisms contribute to lability. Therefore, synapses in the developing brain maintain their capacity for functional AMPA signaling either by being presynaptically silent or by having participated in Hebbian activity; any synaptic activity outside this context leads instead to AMPA silencing and possible synaptic elimination.