Expression of glial fibrillary acidic protein in astrocytes of rat supraoptic nucleus throughout estrous cycle.

OBJECTIVE Oxytocin (OXT) could facilitate preovulatory luteinizing hormone surge in animals and humans while brain OXT production depends on glial fibrillary acidic protein (GFAP)-associated astrocytic plasticity. Here, we examined if GFAP expressions in OXT-producing hypothalamic supraoptic nucleus (SON) correlate to special estrous stages. METHODS 38 adult female rats were classified into diestrus, proestrus, estrus, and metestrus groups determined by vaginal smear. Rats were decapitated and the SON was dissected for detecting Fos and GFAP levels by Western Blot and immunohistochemistry. RESULTS The result showed that Fos expression was significantly high at proestrus compared to other stages in Western blotting. No significant difference in total GFAP expression was observed between rats at different stages of the estrous cycle; however, at proestrus GFAP level at the dorsolateral portion of the SON (a region filled with OXT neurons) was significantly lower than that at the ventro-medial portion in immunohistochemistry. CONCLUSION There is a functional correlation between supraoptic neuron activity and proestrous OXT peak during estrous cycle; it is likely that a plastic change in GFAP expression in astrocytes selectively occurs around OXT neurons at proestrus and facilitates OXT release.