Synaptic boutons are presynaptic varicosities that envelope the machinery that releases neurotransmitter onto the postsynaptic cell. Virtually all synapses are defined by a synaptic bouton including en passent boutons in the central nervous system or end-terminal boutons at the neuromuscular junction. I am working to understand the signaling mechanisms that generate presynaptic varicosities and that control the growth of the synapse.