How It’s Made: The Synapse

Synapse structure and time course of synapse formation. A. Excitatory synapses are composed of a presynaptic terminal positioned opposite a postsynaptic density. The presynaptic terminal contains clusters of neurotransmitter-containing synaptic vesicles and a dense meshwork of proteins that make up the active zone and its matrix. B. In the rodent cortex, synapses are formed during a protracted period. Excitatory synaptogenesis begins during the first postnatal week and peaks during the second week. The bulk of inhibitory synapse formation is delayed relative to excitatory synaptogenesis. Eyes and ear canals open near the end of the second postnatal week. C. Images of cortical excitatory synapses in vitro at 4, 10, and 16 DIV. Images show overlays of VGlut1 (red) and NR1 (green) immunostaining. Scale bar, 10 μm. (DIV, days in vitro.)