Fig. 4.

Histogram showing quantitative cytochrome oxidase (COX) staining intensity [expressed as true optical density (OD)] in the suprachiasmatic nucleus (SCN) of normal untreated control for total sleep-deprived (TSC) and total sleep-deprived rats (TSD) with different sample time-points. In normal untreated and TSC rats, numerous COX-reactive neurons with high true OD were detected in the SCN. In contrast, the staining intensity of COX in the SCN decreased progressively over the duration of TSD. Decreasing COX reactivity was apparent in both the day and night sample groups. *P<0.05 as compared with the day group of normal untreated rats; ††P<0.05 as compared with the night group of normal untreated rats.