The antibody directed against the GluR2/3 subunits of AMPARs was also purchased from Chemicon (now Millipore, cat. no. AB1506). This antibody is directed against the carboxy-terminus of the rat GluR2 and -3 subunits, corresponding to the amino acid sequence EGYNVYGIESVKI (amino acids 850–862), and was generated by immunizing rabbits. Specificity of this antibody was demonstrated by the same studies that characterized the GluR1 antibody, by using Western blot (manufacturer’s data sheet and Petralia and Wenthold, 1992; Wenthold et al., 1992) to show that this antibody recognizes a single band corresponding to the molecular weight, ~108 kDa, of the GluR2/3 subunits and neither the GluR1 nor the GluR4 subunits of AMPARs expressed by COS-7 cells transfected with the respective GluR-subunit cDNA. Previous EM studies (Petralia and Wenthold, 1992), including those from this laboratory (Farb et al., 1995; Farb and LeDoux, 1997, 1999; Levy and Aoki, 2002), had determined that these antibodies recognize asymmetric synapses but not the symmetric synapses of the amygdala and cortex. Asymmetric synapses, in turn, have been shown to be associated with excitatory synapses (Gray, 1959).
