Ovarian cycle-related changes of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat interpeduncular nucleus

The interpeduncular nucleus (IPN) of female rats was studied across the est rous cycle to observe whether the expression of the astroglial marker, glia l fibrillary acidic protein (GFAP) reacts to hormonal changes in an area no t belonging to the 'endocrine brain'. A marked reduction of immunoreactive GFAP was observed in estrus as compared to the immunoreactivities in met- a nd proestrus. This finding is consistent with earlier observations in the e ndocrine hypothalamus, but also proves that gonadal steroids influence astr oglia in brain regions not involved in neuroendocrine regulation. Since cyc lic fluctuations of synaptic numbers in the female have been described only for the endocrine hypothalamus, decrease of immunoreactive GFAP in the IPN during estrus may reflect a down-regulation of CFAP synthesis. (C) 2000 El sevier Science B.V. All rights reserved.