GluR1 and GluR2/3 immunoreactivities were considered synaptic when PEG particles were detected precisely over the PSD or within 60 nm from the postsynaptic membrane surface (black arrows in Fig. 4 and schematized in Fig. 3). PEG particles occurring within the synaptic cleft of asymmetric synaptic junctions were also included in the tally of “synaptic” immunolabeling. Immunoreactivity was considered to be nonsynaptic, although it was potentially and functionally linked to the synapse, when the PEG particles occurred at a position >60 nm from the postsynaptic membrane surface of the spine but still within the cytoplasm of the spine (white arrows in Fig. 4 and schematized in Fig. 3).
