LOCALIZATION OF AMPA-SELECTIVE GLUTAMATE-RECEPTOR SUBUNITS IN THE ADULT CAT VISUAL-CORTEX

We have studied the presence and distribution of pha-amino-3-hydroxy-5 -methyl-4-isoxazolepropionate (AMPA)-selective glutamate receptor subu nits (GluR1, 2, 3, and 4) in the adult cat visual cortical areas 17, 1 8, 19, and the lateral suprasylvian areas (LSA). Reverse transcription -polymerase chain reaction (RT-PCR) amplification indicated that the g enes encoding GluR1, 2, 3, and 4 are expressed in these areas and West ern blot analysis revealed that the size of the corresponding peptides is similar to those described in the rat brain. In situ hybridization (ISH) using digoxigenin-labeled riboprobes showed that mRNAs coding f or GluR1 and GluR3 were located in cells in all layers of the areas ex amined and also in the underlying white matter. GluR1 mRNA was relativ ely abundant throughout layers II-VI while GluR3 mRNA revealed a more laminated pattern of expression, preferentially labeling cells in laye rs II, III, V, and VI. The distribution of AMPA-selective receptor sub unit peptides was studied by immunohistochemistry using subunit specif ic antibodies and found to be consistent with ISH results. In addition , we observed that most of the cells strongly labeled by the anti-GluR 1 antibody were non-pyramidal neurons and that intense GluR2/3 immunor eactivity was seen preferentially in pyramidal neurons. Interestingly, double-labeling experiments indicated that neurons expressing gamma-a minobutyric acid (GABA) as well as the GluR1 subunit were particularly abundant in deeper layers. The GluR4 peptide was predominantly found in a relatively low number of layer III and layer V neurons with eithe r pyramidal or non-pyramidal morphology. Finally, the distribution of neurons expressing the various receptor subunits was similar in all th e visual cortical areas studied. These findings indicate a high expres sion of GluR1-3 subunits in the cat visual cortex and that GluR1 and G luR2/3 subunits are particularly abundant in non-pyramidal and pyramid al neurons, respectively. In addition, the results described here prov ide a reference for future studies dealing with the effect of visual d eprivation on the expression of this receptor type.