Initial survey of grids prepared from tissue containing the LA of naïve rats indicated that the procedure yielded GluR1 immunolabeling of approximately 20% of spines and none of the symmetric (presumably inhibitory) synapses, with a substantial portion of the PEGs occurring non-synaptically (white arrows in Fig. 4). In contrast, the identical PEG procedure but using the GluR2/3 antibody, in lieu of the GluR1 antibody, yielded immunolabeling of approximately 70% of spines, with the majority of them exhibiting PEG directly over the PSD (black arrows in Fig. 4). These differences indicated that a larger portion of asymmetric synapses utilize AMPARs that contain the GluR2/3 subunits than the GluR1 subunits. This pattern was recaptured by light microscopy, which showed that GluR2/3 immunolabeling of the neuropil is robust and evenly distributed across subregions of the amygdala and at levels comparable to those found in the cortex and caudate-putamen nucleus, whereas the GluR1 immunoreactivity is relatively sparse, especially within the LA (Fig. 2).
