Birth, growth and elimination of a single synapse.

Synapses are functional units regulating information flows in the neuronal circuits. How synaptic junctions are formed and remodelled is a fundamental question in developmental neurobiology. In recent years, it has become possible to visualize the formation, maintenance and remodelling of a single synapse by using new imaging methods. These studies, identifying synaptic structures by lipophilic dye markers and genetically modified synaptic molecules with fluorescent proteins, provided new insights into synapse development and maturation. Experimental evidence indicates very rapid assembly of both presynaptic and postsynaptic marker proteins at newly formed synaptic junctions. Morphological expansion of the synaptic junctional membrane is tightly coupled to both efficacy of the presynaptic neurotransmitter release and postsynaptic receptor distribution. The elimination process of pre-existing synapses has also been reported, and evidence for persistent remodelling of synaptic junctions has been provided. Information regarding birth, maturation and elimination of a single synapse is accumulating and will influence our concepts about how neuronal circuits are organized and maintained.