Glucocorticoids up-regulate the expression of glial fibrillary acidic protein in the rat suprachiasmatic nucleus.
Immunoreactivity against glial fibrillary acidic protein (GFAP) was used as a dynamic index in adrenalectomized rats subjected or not to corticosterone replacement to investigate whether glucocorticoids may interact with astrocytes in the suprachiasmatic nucleus (SCN), the master component of the central circadian clock. GFAP staining in the SCN was significantly higher in rats having received implants that restored physiological plasma levels of corticosterone within diurnal or nocturnal limits than in non-normalized rats. The effects of corticosterone were similar in the parvocellular portion of the paraventricular nucleus but were opposite in the hippocampus, another major site of negative feed-back regulation of the hypothalamic-pituitary-adrenal axis, where a decreased GFAP staining was observed in discrete regions of the dentate gyrus. This indicates that glucocorticoids may positively or negatively regulate GFAP, depending on the target brain structure. In the SCN, that contains only few if any glucocorticoid receptors, indirect mechanisms that may involve serotoninergic neurons are probably responsible for the effects of corticosterone level. It is proposed that the corticosterone-induced increase in GFAP staining in that nucleus accounts for dynamic changes in neurone-astrocyte interactions that might occur in relation with natural fluctuations of glucocorticoids over the 24 h period.
Maurel
D
D
Interactions Fonctionnelles en Neuroendocrinologie, INSERM, Institut Fédératif Jean-Roche, Université de la Méditerranée, Marseille, France. maurel.d@jean-roche.univ-mrs.fr
Sage
D
D
Mekaouche
M
M
Bosler
O
O
D000315:Adrenalectomy; D000818:Animals; D002940:Circadian Rhythm; D003345:Corticosterone / Q000494:pharmacology; D018891:Dentate Gyrus / Q000187:drug effects / Q000378:metabolism; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism*; D005938:Glucocorticoids / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D009473:Neuronal Plasticity / Q000502:physiology; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D015854:Up-Regulation
D005904:Glial Fibrillary Acidic Protein; D005938:Glucocorticoids; D003345:Corticosterone