Immunohistochemical studies of localization and co-localization of glutamate, aspartate and GABA in the anterior thalamic nuclei, retrosplenial granular cortex, thalamic reticular nucleus and mammillary nuclei of the rat

Localization and possible co-localization of glutamate, aspartate and GABA immunoreactivities was examined in the anterior thalamic nuclei, retrosplenial granular cortex, thalamic reticular nucleus and mammillary nuclei of the rat by double antigen immunohistochemistry using diaminobenzidine and benzidine dihydrochloride in one series and double immunofluorescence labelling with rhodamine and fluorescein in a second series of animals. In three of these regions, retrosplenial granular cortex, anterior thalamic nuclei, and mammillary nuclei, glutamate immunoreactivity was co-localized with aspartate immunoreactivity in a majority of the projection neurons (pyramidal neurons, predominantly in layers V and VI in retrosplenial granular cortex; rounded polygonal multipolar neurons throughout the rostrocaudal extent of the anterior thalamic and mammillary nuclei). None of the cells showing glutamate and/or aspartate immunoreactivity in these regions also displayed GABA immunoreactivity, which was present in non-pyramidal cells in the retrosplenial granular cortex (chiefly in layers I–III) and in small numbers of cells within the anterior thalamic nuclei. In the thalamic reticular nucleus, in contrast, most neurons were immunoreactive for GABA and in the majority of these neurons glutamate (and/or aspartate) immunoreactivity was co-localized with GABA.