New Patterns of NeuroendocrineInteractions: Role of Glial Cells

Overview

Hormones regulate several aspects of neuronal activity, but less isknown of their effects on glia. Thyroid hormones and estrogens influenceglial function, e.g. stimulate oligodendrocytic production of myelin duringearly development and, possibly, in adulthood. The gliosis, characteristic ofthe aging brain has been interpreted as a secondary, compensatory responseto a progressive age-associated decline in number and function of neurons.Current evidence shows that the capacity of neurons to divide is not limitedto early development (as formerly believed), but, rather may be extendedthroughout the lifespan by endogenous mechanisms. Glial cells, an importantcomponent of the neuronal micro-environment would play a key role in mo-dulating neuronal plasticity. In our experiments reported here, the ovariansteroid, 17b-estradiol, and the „designer“, non-steroidal estrogen, tamoxifen,effectively protected cultured C-6 glioma 2B clone cells from the cytotoxicityof the excitatory neurotransmitter, glutamate, significantly reducing cell de-ath, estradiol being the most effective. Estradiol and tamoxifen also stimula-ted cell maturation as assessed by increased marker enzyme activity andmorphological characteristics. Thus, estrogens often used in therapy (estra-diol as replacement after menopause and tamoxifen for treatment/preventionof breast cancer) significantly protect glial cells against glutamate toxicityand stimulate cell differentiation and maturation. Hormonal ability to modu-late glial activity and, indirectly, to regulate glial-neuronal interactions mayopen new avenues to prevention/treatment of brain damage and aging-asso-ciated neurodegenerative disease.

Key words:
glia, estrogens, triiodothyronine, CNS plasticity.