Abstract
The aim of the present study was to examine whether a 3-h spontaneous wheel-running could entrain the mouse circadian rhythm under constant darkness (DD). Four-month-old, male, wild type mouse (n=27, C57BL6J, CLEA Japan, Inc) were used. They were raised in own animal quieter where environmental conditions were kept constant (light from 6:00 to 18:00, light intensity ca 100 lx, room temperature 22±2°). At 4 month old age, they were transferred to individual cage without running-wheel. The animals were exposed to DD for 4 weeks to establish stable free-running rhythm. Then the cage were exchanged with a cage out-fitted with a running-wheel (10cm diameter) for 3-h, 3-h from 6:00 to 9:00 of local time. Wheel running treatment was implemented for 80-100 days with a fixed period of 24-h. Afterwards, the spontaneous locomotor activity was measured in DD for 4 weeks. As a result, 15 of 23 mice entrained the scheduled 3-h wheel-running session. The timing of wheel setting during entrainment was related (-0.644, p<0.008) to free-running period before treatment under DD, when 3-h wheel running commenced the late subjective night (CT 17-22, CT12 was activity onset of animal). 6 animals showed longer free-running periods than 24-h ranged 24.04-24.44, and their free-running periods were significantly shortened after 3-h wheel treatment (M±SD, 23.93±0.07h). A possible role of 3-h wheel running was demonstrated as the non-photic zeitgeber. [J Physiol Sci. 2006;56 Suppl:S208]
