Androgen receptor immunoreactivity in forebrain axons and dendrites in the rat

As members of the steroid receptor superfamily, androgen receptors (ARs) have been traditionally identified as transcription factors. In the presence of ligand, ARs reside in the nucleus, where, upon ligand binding, the receptors dimerize and bind to specific response elements in the promoter region of hormone-responsive genes. However, in this report, we describe the discovery that ARs are also present in axons and dendrites within the mammalian central nervous system. AR expression in axons was identified in the rat brain at the light microscopic level using two different antibodies directed against the N terminus of the AR protein and nickel intensified 3'-3'-diaminobenzidine, and also using fluorescence methods and confocal microscopy. This distribution was confirmed at the ultrastructural level. In addition, AR immunoreactivity was identified in small dendrites at the ultrastructural level. AR-immunoreactive axons were observed primarily in the cerebral cortex and were rare in regions where nuclear AR expression is abundant. The observation that ARs are present in axons and dendrites highlights the possibility that androgens play an important and novel extra-nuclear role in neuronal function.