In the light microscopic portion of the present study, we noted that GluR1 immunoreactivity in the LA is much lower than is the GluR2/3 immunoreactivity. This pattern is predicted from earlier studies, indicating that GluR1 immunoreactivity occurs predominantly in inhibitory aspiny interneurons of the basolateral amygdala, whereas the GluR2/3 immunoreactivity occurs much more prevalently within the spiny, pyramidal-like neurons (McDonald, 1996), combined with the fact that many more of the neurons in the LA are excitatory than are inhibitory (Johnson et al., 2001). Based on this observation, the lower level of GluR1 immunoreactivity that we detected by the PEG procedure (~20%), relative to the GluR2/3 immunoreactivity that we detected by using the same procedure (~70%), is likely to reflect, at least in part, differences in GluR1 versus GluR2/3 antigen levels, rather than the failure to detect the GluR1 antigen.
