Localisation of ionotropic glutamate receptor subunits, and gamma-aminobutyric acid (GABA) in the monkey amygdala--a double immunolabelling and electron microscopic study.

The distribution of ionotropic glutamate receptor subunits GluR1 and NMDAR1, and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) was studied by immunocytochemistry, in the monkey amygdala. The basal and lateral nuclei contained a higher density of GluR1-positive neurons than the corticomedial and central groups of nuclei, and the accessory basal nucleus. A higher density of NMDAR1 immunopositive cell bodies was also present in the lateral nucleus, compared to the other nuclei of the amygdala. Large multipolar or fusiform projection neurons, and not small local circuit neurons were GluR1 or NMDAR1-positive, and less than 0.5% of the GluR1-positive cells were double labelled for GABA. In contrast, almost all GluR1-positive neurons were also labelled for NMDAR1 in double labelled sections and vice versa. Electron microscopy also showed that GluR1- and NMDAR1-positive cells had distinctive ultrastructural features, compared with GABAergic cells, ant that there was very rare colocalisation, between GABA, and GluR1 or NMDAR1-positive cell bodies or dendrites. It is likely that not all projection neurons were GluR1 or NMDAR1-positive, however, since GluR1 or NMDAR1-positive neurons were only 2-3 times as common as GABAergic cells, whereas it has been estimated that projection neurons outnumber GABAergic local circuit neurons by 4 to 1 (McDONALD and AUGUSTINE, 1993; PITKANEN and AMARAL, 1994).