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By means of immunohistochemical and electrophysiological methods, we have investigated the presence of androgen receptors on astrocytes in explant and primary cultures from various regions of rat central nervous system. Our studies have shown that a great number of astrocytes and neurones express androgen receptors as recognized by a specific monoclonal antibody. Immunoreactivity was mainly distributed over the soma of the astrocytes, the nuclei being intensely stained. In contrast, glial processes were only faintly stained or not stained. Double-immunostaining studies have provided evidence for a colocalization of androgen and estrogen alpha- and beta-receptors on many astrocytes. Furthermore, there was also a coexistence of glial androgen receptors with cholinergic muscarinic and nicotinic sites. Our immunohistochemical findings are supported by electrophysiological investigations demonstrating that 5alpha-androstan, 17beta-estradiol as well as the cholinergic agonists muscarine and nicotine caused hyperpolarizations on the same astrocytes. Our studies suggest that there is a coexistence of functional receptors for androgen, estrogen as well as for the cholinergic agonists on glial cells. Further investigations are needed to elucidate the physiological role of glial androgen, estrogen and cholinergic receptors and to define their function in neurodegenerative diseases.

Autoradiographic studies have shown that many neurones in explant cultures of rat neocortex, hippocampus, preoptic area and spinal cord express binding sites for [3H]-estradiol which are distributed over the cell bodies and primary processes. By means of immunohistochemistry, it was observed that neurones were labelled by monoclonal antibodies against estrogen alpha-receptors and a polyclonal antibody against estrogen beta-receptors. Immunoreactivity was distributed over the soma and primary processes of the cells, the nuclei being more intensely stained. Double-immunostaining revealed a colocalization of estrogen alpha- and beta-receptors on approximately half of the neurones in cultures from neocortex and hippocampus whereas in cultures from preoptic area and spinal cord only few cells were double-stained. On many neurones, a coexistence of estrogen receptors and cholinergic muscarinic or nicotinic sites was found. Furthermore, combined autoradiographic and immunohistochemical studies have shown a colocalization of receptors for estrogen and the neuropeptide [125I]-galanin. The coexistence of estrogen and cholinergic sites as well as of estrogen and galanin receptors on the same neurones are discussed with respect to neurodegenerative events such as Alzheimer's disease.

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