We performed dual electron microscopic immunocytochemistry to determine the precise cellular relations between β-adrenergic receptors (βAR) and Catecholaminergic terminals within adult rat brains. An antibody, βAR404, against a peptide corresponding to the C-terminus of the hamster lung βAR (β2 subtype) together with an anti-tyrosine hydroxylase (TH), a Catecholaminergic marker, were used. Results show predominant labeling for βAR404 within small astrocytic processes (β-A). This is in sharp contrast to earlier results which showed neuronal labeling when using antibodies against the third intracellular loop of the receptor and of neurons-plus-astrocytes labeled using antibodies against the whole βAR molecule. β-A within visual cortex and nuclei of the solitary tracts frequently contacted blood vessel basement membrane and TH-immunoreactive terminals. TH-immunoreactive axons forming axo-axonic juxtapositions with non-TH terminals were also noted to be surrounded by β-A. In the area postrema, a brain region lacking a blood-brain barrier, few β-A occurred adjacent to TH-immunoreactive terminals or elsewhere. Thus, 1) catecholamines may act beyond morphologically identifiable synapses; 2) β-A may mediate interactions between catecholamines and other transmitters; 3) there may be substantial heterogeneity in the structure or the conformation of the βAR protein between neurons and glia or across CNS regions.
- β-Adrenergic receptors β-Adrenoceptors Astrocytes Nucleus of the solitary tract Area postrema Visual cortex Catecholamines Ultrastructure Blood-brain barrier Synapse Circumventricular organ Area postrema
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