Activity rhythms and photoperiodism of Syrian hamsters in a simulated burrow system

Male Syrian hamsters were housed in simulated burrows in order to investigate (a) how these nocturnal, fossorial rodents entrain to the prevailing light:dark cycle in this semi-natural habitat and (b) the response of the reproductive system to environmental illumination. The burrow emergence activity of hamsters housed in simulated burrows was compared to the running wheel activity of animals maintained in standard cage conditions. The activity rhythm was similar in both measuring devices. The data suggested that in a natural environment hamsters are only exposed to light for short amounts of time each day. To determine whether brief photoperiodic stimulation could alter the phase angle of entrainment and/or the reproductive condition, burrow housed animals were exposed to a supplemental 30-second light pulse during specified clock hours of the dark period on a daily basis. These light pulses induced a phase shift and maintained a long day reproductive response in what was otherwise a short photoperiod.