Daylight and Artificial Light Phase Response Curves for the Circadian Rhythm in Locomotor Activity of the Field Mouse Mus booduga

Abstract

The sensitivity of the circadian pacemaker of the field mouse Mus booduga to diffuse daylight pulses of 15 min duration and 1000 lux intensity was measured in a series of experiments and a phase response curve (PRC) constructed. The PRC evoked was of type-I with significant quantitative differences compared to the PRCs constructed for other light stimuli (fluorescent and incandescent light sources) of the same intensity and duration. Not only are the advance and delay peaks larger in the daylight PRC, but there is also significant qualitative and quantitative differences in the shape of the PRC. The area under the advance zone of the diffuse daylight PRC (A) was found to be significantly greater than the A of (i) the fluorescent light PRC and of (ii) the incandescent light PRC. The area under the delay zone of the diffuse daylight PRC (D) was also found to be significantly greater compared to D of (i) the fluorescent light PRC and of (ii) the incandescent light PRC. These differences in the shape of the PRCs can only be attributed to the variation in the spectral intensity distribution of the different components in the three light stimuli used since all other factors (e.g. sample size, free-running period, duration and intensity of light pulse etc.) were comparable in the three PRC experiments. We conclude that the circadian photoreceptor(s) of the field mouse M. booduga are sensitive to variations in the spectral composition of light stimuli.

The ecological impacts of nighttime light pollution: a mechanistic appraisal

“…Melatonin production is similarly reduced in rats under nighttime light levels of 0.2 lux (Dauchy et al, 1997), and in hamsters at levels above 1 lux (Brainard et al, 1982), and has been shown to suppress immune responses and increase the rate of tumour growth (Dauchy et al, 1997;Bedrosian et al, 2011b). Similar Sharma et al (1997) *Converted from reported values in foot candles. Note that: (i) in many cases these represent levels of experimental treatments, and precisely where thresholds might lie remains unknown; and (ii) although widely used, lux measurement places emphasis on brightness at wavelengths perceived by human vision.…”

In the field mouse Mus booduga melatonin phase response curves (PRCs) have a different time course and wave form relative to light PRC

“…hooduga remains sensitive to melatonin throughout the subjective day, thus exhibiting a lack of a distinctive refractory zone. A higher dose of melatonin (10 mg/kg) evokes phase shifts of magnitude comparable to the magnitude of lightinduced phase shifts (Sharma et al, 1997).…”

“…The field mouse Milts hooduga was chosen for the present study because of its precise, robust, and easily measured circadian rhythm in locomotor activity. The response of activity rhythm to light stimuli has also been well studied in these mice [Sharma, 1996;Sharma and Chandrashekaran, 1997;Sharma et al, 19971. The lightinduced PRC is of type-1, with delays dominating during early subjective night, advances during late subjective night, and minimal but non-zero phase shifts during the subjective day [Sharma et al, 19971.…”

Precision of a Mammalian Circadian Clock

“…2) along with a unique shape of the phase response curve evoked by light [8,9] could possibly explain the functional importance of the dependency of clock precision on the free-running period. 2) along with a unique shape of the phase response curve evoked by light [8,9] could possibly explain the functional importance of the dependency of clock precision on the free-running period.…”