IMMUNOHISTOCHEMICAL DETECTION OF A(1) ADENOSINE RECEPTORS IN RAT-BRAIN WITH EMPHASIS ON LOCALIZATION IN THE HIPPOCAMPAL-FORMATION, CEREBRAL-CORTEX, CEREBELLUM, AND BASAL GANGLIA

Polyclonal antisera were generated against two identical regions of rat and human A(1) adenosine receptors using synthetic multiple-antigenic-peptides as immunogens. Western blotting showed that the antisera recognized a single protein in brain of the expected size for A(1) receptors. Immunohistochemistry of CHO cells transfected with the rat or human A(1) adenosine receptor cDNAs showed robust labeling of the cell surface. In contrast, labeling was not apparent over non-transfected CHO cells, nor over CHO cells expressing A(2a) receptors. The pattern of immunoreactivity in rat brain was similar to that expected for A(1) adenosine receptors. In contrast to receptor autoradiography or in situ hybridization methods, immunohistochemistry allowed identification of individually labeled cells and processes. Heavy labeling was apparent in many brain regions. In the hippocampal formation, strong labeling was present on granule cell bodies and dendrites, messy fibers, and pyramidal neurons. In cerebellum basket cells were the most heavily labeled cell type. Less intense staining was present over granule cells. In cerebral cortex, pyramidal cells were the most heavily labeled cell type, and some interneurons were also labeled. In the basal ganglia, 43% of neurons in the globus pallidus were labeled. In the caudate-putamen region, 38% of neurons were labeled. Heavy labeling was present in most thalamic nuclei, and moderate to heavy labeling was seen in many brainstem nuclei. These data identify specific cellular sites of A(1) receptor expression and support the concept of cellular specificity of A(1) adenosine receptor action.