A highly sensitive immunofluorescence procedure for analyzing the subcellular distribution of GABAA receptor subunits in the human brain

We designed a protocol to improve the immunohistochemical analysis of human brain structures, which overcomes the limited detection sensitivity, high background, and intense autofluorescence commonly associated with human tissue. This procedure was evaluated by using antibodies against major GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3), gamma(2)) in autopsy and surgical specimens. Tissue blocks were briefly fixed by immersion and pretreated with microwave irradiation in sodium citrate buffer. Immunoperoxidase staining revealed a marked enhancement of cell surface immunoreactivity and reduction of background in microwave-irradiated tissue, irrespective of its origin. For confocal laser scanning microscopy, immunofluorescence staining was optimized with the tyramide signal amplification (TSA) technique. This procedure not only dramatically increased the sensitivity for antigen detection but also totally suppressed autofluorescence, thus revealing the cellular and subcellular distribution of GABAA receptor subunits. A distinct neuron-specific expression pattern of the alpha-subunit variants was observed in cerebral cortex and hippocampal formation, along with widespread expression of the gamma(2)-subunit. Of particular interest was the prominent alpha(2)- and alpha(3)-subunit staining on the initial axon segment of pyramidal neurons. This protocol represents a major improvement for high-resolution studies of human brain tissue aimed at investigating morphological alterations underlying neurological diseases.