Histochemical and electrophysiological evidence for estrogen receptors on cultured astrocytes: colocalization with cholinergic receptors

By means of autoradiographic and immunohistochemical methods it was demonstrated that astrocytes in explant and primary cultures of rat neocortex, hippocampus, preoptic area and spinal cord express estrogen α‐ and β‐receptors. Immunoreactivity was mainly distributed over the soma, the nuclei being more intensely stained. Combined autoradiographic and immunohistochemical studies as well as double‐immunostaining revealed a colocalization of estrogen α‐ and β‐receptors on many astrocytes. There was also a coexistence of estrogen receptors and cholinergic muscarinic and nicotinic sites. Electrophysiological investigations have shown that 17β‐estradiol induced hyperpolarizations on the majority of astrocytes in explant cultures of hippocampus and spinal cord, providing evidence for the existence of functional estrogen receptors on these cells. Furthermore, on the same astrocytes, 17β‐estradiol, muscarine and nicotine caused hyperpolarizations, suggesting a coexistence of receptors for estrogen and the cholinergic agonists on glial cells. The presence of glial estrogen receptors and their colocalization with cholinergic receptors is discussed with respect to the effects of these neurotransmitters/neuromodulators in development and maturation of the central nervous system, as well as to neurodegenerative events such as Alzheimer's disease.