Distribution of the AMPA2 glutamate receptor subunit in adult cat visual cortex

Abstract In this study, we revealed the distribution of the AMPA2 glutamate receptor subunit (AMPA2) in the visual cortical areas 17 and 18 of the adult cat by means of different techniques. In situ hybridization, with a cat-specific radioactively labeled oligonucleotide probe, showed that AMPA2 mRNA was expressed mainly in cortical layers II/III and V/VI with a lower expression in layer IV and practically no signal in layer I. Immunocytochemistry, using a polyclonal AMPA2 subunit-specific antibody, showed immunoreactivity almost exclusively in the somata and dendrites of pyramidal neurons in cortical layers II/III and V/VI. Only a very faint signal was detected in layer IV. Neurons with little or no AMPA2 have AMPA receptors that are highly permeable to calcium. By determining the location of AMPA2, this study therefore provides a clear examination of the distribution of Ca 2+ -impermeable AMPA receptors over the supra- and infragranular layers of cat visual cortex. The functional implication of the absence of AMPA2 in cortical layer IV and thus the presence of Ca 2+ -permeable AMPA receptors in this layer, is still speculative and has yet to be elucidated.