Chapter Three – The First Hour in the Life of a Synapse: Contact Formation, Partner Selection, and Onset of Function

The brain contains trillions of synapses which specifically connect neurons, often with subcellular precision. The formation of a synapse involves a complex series of steps that occur in a particular order. Remarkably, during development, all the steps can be completed and result in a functional synapse within 1 h. Here we will describe the processes involved in forming a synapse from initial contact formation, to partner selection, through to onset of function. Specifically, we will explain the role that filopodia play in seeking and selecting correct axons for synapse formation. We will highlight the differences between formation of excitatory and inhibitory synapses. We will describe how specificity is signaled during partner selection and highlight key adhesion molecules that may be involved in this process. In addition, we will outline how formation of pre- and postsynaptic terminals is fundamentally different. Finally, we will discuss the role of activity in every step of the process of synapse formation, including its role in the onset of function.