PER is variably expressed in the neuropil ensheathing glia. Ensheathing glia are labeled with GFP (arrowheads) in NP6520-GAL4>GFP brains. (A) PER signal is detected in a subset of GFP-positive cells at ZT22 in the central brain of 5 and 55 day old flies. PER levels vary from cell to cell. No PER was detected in young or old brains at ZT10 (data not shown). Scale bars equal 10 μm. (B) Brain outline indicating location of cells shown in (A) in the region of the ventral central brain. (C) Graph showing the average relative PER fluorescence in ensheathing glia. PER levels are not significantly different between young and old flies (p = 0.8452, t = 0.2017, df = 7.961). Number of brains analyzed are shown within each bar; error bars indicate SEM.