Impact of a Single Episode of Different Intensity of White Light Pulse at Night on Masking Response in the Diurnal Mammal, Funambulus pennantii

Abstract

Objective: Light affects mammalian circadian rhythms through entrainment and masking. Photic masking increases locomotor activity in diurnal species (positive masking) while reducing activity in nocturnal species (negative masking). Fewer studies have investigated masking in diurnal rodents. We investigated the masking response in a diurnal rodent, <i>Funambulus pennantii</i> when subjected to white light pulses of different intensities at night between zeitgeber time (ZT) 12 and ZT 15.Methods: Adult male squirrels, <i>F. pennantii</i> (n=10/group, three groups) were placed in individual cages with running wheels under standard 12:12 h light-dark (LD) conditions. Recording of the locomotor activity rhythm was carried out using a ClockLab setup. Following a week of stable entrainment to the LD cycle, the animals of each group were given a sham exposure. After 10 days, animals of group I, II, and III were exposed to 3-h white light pulses of 100 lux, 10 lux, and 1 lux, respectively, between ZT 12 and ZT 15. Following the exposure, the animals were allowed to run undisturbed for 7 days.Results: Compared to the shamexposed group, exposure to 3-h 1 lux, 10 lux, and 100 lux artificial light pulses at night caused positive masking, stimulating wheel running in an intensity-dependent manner. Additionally, nighttime light pulses of 100 lux and 10 lux reduced onset accuracy, reduced the amplitude of the rhythm, and also altered the phase angle relationship to light.Conclusion: The positive masking caused by light exposure at night in diurnal squirrels is intensity-dependent up to at least 100 lux and is associated with a dampening of circadian rhythms.