Involvement of glial fibrillary acidic protein (GFAP) expressed in astroglial cells in circadian rhythm under constant lighting conditions in mice

To clarify the role of glial fibrillary acidic protein (GFAP)‐expressed glial cells in the circadian clock, we examined GFAP expression in the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) under various lighting conditions in mice. We demonstrated that GFAP expression did not show daily change in the SCN under a light‐dark cycle; however, long‐term housing under constant lighting conditions led to dramatic changes in GFAP expression, i.e., a decrease in the SCN and an increase in the IGL. Furthermore, mice that had a targeted deletion in the GFAP gene (GFAP mutant mice) showed longer and more arrhythmic circadian activity rhythms in constant lighting conditions than wild‐type mice, while GFAP mutant mice exhibited stable circadian rhythms both in a light‐dark cycle and constant darkness, and showed normal entrainment to environmental light stimuli. These results suggest that the GFAP‐expressed astroglial cells in the SCN and the IGL may have some role in circadian oscillation under constant lighting conditions. J. Neurosci. Res. 60:212–218, 2000 © 2000 Wiley‐Liss, Inc.