DIFFERENTIAL LOCALIZATION OF NMDA AND AMPA RECEPTOR SUBUNITS IN THE LATERAL AND BASAL NUCLEI OF THE AMYGDALA - A LIGHT AND ELECTRON-MICROSCOPIC STUDY

Anatomical and physiological studies indicate that the amino acid L-gl utamate is the excitatory transmitter in sensory afferent pathways to the amygdala and in intraamygdala circuits involving the lateral and b asal nuclei. The regional, cellular, and subcellular immunocytochemica l localizations of N-methyl-D-aspartate (NMDA) and L-alpha-amino-3-hyd roxy-5-methyl-4-isoxazole propionate (AMPA), two major classes of glut amate receptors, were examined in these areas of the amygdala. A monoc lonal antibody and a polyclonal antiserum directed against the R1 subu nit of the NMDA receptor were used. Each immunoreagent produced distin ct distributions of perikaryal and neuropilar staining. Dendritic immu noreactivity was localized primarily to asymmetric (excitatory) synapt ic junctions, mostly on spines, consistent with the conventional view of the organization and function of NMDA receptors. Whereas the anti-N MDAR1 antiserum produced sparse presynaptic axon terminal labeling and extensive glial labeling, the anti-NMDAR1 antibody labeled considerab ly fewer glia and many more presynaptic axon terminals. Labeled presyn aptic terminals formed asymmetric and symmetric synapses, suggesting p resynaptic regulation of both excitatory and inhibitory transmission. Immunoreactivity for different subunits of the AMPA receptor (GluR1, G luR2/3, and GLuR4) was uniquely distributed across neuronal population s, and some receptor subunits were specific to certain cell types. Imm unoreactivity for GluR1 and Glu2/3 was predominately localized to dend ritic shafts and was more extensive than that of GluR4 due to heavy la beling of proximal portions of dendrites. The distribution of GluR4 im munoreactivity was similar to NMDAR1: GluR4 was seen in presynaptic te rminals, glia, and dendrites and was primarily localized to spines. Th e presynaptic localization of GluR4 in the absence of GluR2 suggests g lutamate-mediated modulation of presynaptic Ca++ concentrations. These data add to our understanding of the morphological basis of pre- and postsynaptic transmission mechanisms and synaptic plasticity in the am ygdala. (C) 1995 Wiley-Liss, Inc.