Enhanced bioluminescence signal stability following oral versus injected luciferin delivery.

A: Average maximum signal from a freely moving female mouse imaged with the Evolve EMCCD camera after luciferin injection (first arrow) shows the predicted rapid decline over the next hour. The first point was adjusted to correct for different camera settings. Oral luciferin provided to the same mouse (second arrow) before the time when circadian activity begins, near projected dusk (hour 12), produced a rapid and sustained signal. Bars below show the light and dark phases of the light cycle before the recording. B: Average pixel intensity of three freely moving mice provided with oral luciferin at three time points around the end of the day (long arrows) and imaged with the non-EMCCD camera (CH360) and 60-minute exposures to integrate the signal. Luciferin delivered before projected dusk produced a rapid rise in signal in long (Mouse 1) and short (Mouse 2) recordings. Luciferin provided after projected dusk produced a slower increase in signal (Mouse 3) that converged with the level achieved by Mouse 1 including the dip in signal following projected dawn (short arrow). Shown is integrated whole animal bioluminescence without any selection for the posture of the mouse or its position within the field of view. C: A fourth mouse imaged with the non-EMCCD camera and provided with oral luciferin five hours below the projected night shows a similar temporal pattern of bioluminescence including the dip in signal after projected dawn. Lines in B and C are 5-point running averages.