Ultraviolet-light-evoked phase shifts in the locomotor activity rhythm of the field mouse Mus booduga.

The circadian rhythm of locomotor activity in the nocturnal field mouse Mus booduga has been monitored after an exposure to ultraviolet-A (UV-A; wavelength between 350 and 400 nm) radiation at various hours of the subject's cycle. The magnitude of the phase shift is used to determine the sensitivity of the circadian pacemaker underlying locomotor activity rhythm. It is observed that UV-A shifts the phase of the locomotor activity rhythm in a phase-dependent manner. A phase response curve (PRC) is constructed to depict the time course and waveform of the basic oscillator's sensitivity to UV-A radiation. The UV-A PRC qualitatively resembles the PRC constructed using diffused daylight as stimulus. Furthermore, the phase response characteristics of the circadian pacemaker for UV-A suggest a periodically varying sensitivity to UV-A similar to that to daylight.