Circadian fluctuations in GFAP distribution in the Syrian hamster suprachiasmatic nucleus.

We examined the possibility that astrocytes reflect mammalian circadian rhythmicity by observing the astrocytes pattern using anti-glial fibrillary acidic protein (GFAP), within the suprachiasmatic nucleus of the Syrian hamster over the 24 h cycle. Our results reveal daily systematic changes in the distribution of GFAP-immunoreactivity (GFAP-ir) both in the light/dark cycle and in constant darkness. This rhythm is characterized by a change of the GFAP-ir distribution from a network pattern to isolated cells. Such a rhythm is in synchrony with the rhythm in SCN glucose consumption which we have previously reported. This is the first time a circadian rhythm in suprachiasmatic astrocytes has been observed, indicating that GFAP-ir can be used as a novel index of clock activity.