Fig 1.

SCN from aged rats display robust circadian oscillations in vitro. Representative circadian rhythms of Per1-luc luminescence from cultured SCN explanted from young (A) and aged (B) rats. The tissue was explanted just before lights-off (arrows). Light output (in counts/min) is plotted against previous light onset (hour 0). Four SCN from aged rats were maintained in vitro for 40 days before recording (two examples are shown in C and D). Circadian rhythms persisted in all four explants, and as expected, the explants were out of phase with one another after 40 days in culture.