Fig. 2. PSD95-GFP specifically localizes to ultrastructurally identified synapses on tectal neuron dendrites. (A-C) The localization of PSD95-GFP was determined by examining the distribution of GFP immunoreactivity by electron microscopy. The electron photomicrographs show specific localization of GFP immunoreactivity as revealed by the silver-enhanced gold particles (open arrows) at postsynaptic terminals. Morphologically mature synapses (black arrows), containing presynaptic terminals with numerous synaptic vesicles (v) and clearly defined pre- and postsynaptic specializations are observed. The silver enhanced gold particles were directly localized to the postsynaptic membrane at the postsynaptic density (A-C), or were within 200 nm of the postsynaptic density (B). Scale bar: 200 nm.