Entrainment by daily light pulses at random times in a subterranean rodent (Ctenomys aff. knighti)

FLÔRES, DANILO EFL; ODA GISELE A; VALENTINUZZI VS

Florida

Congreso; Society for Research in Biological Rhythms; 2012

SRBR

South American subterranean rodents commonly known as tuco-tucos (Ctenomys aff. knighti) spend most of the time inside dark burrows but expose themselves to light briefly, at random times during the daylight hours. This daily light exposure pattern may be sufficient for light/dark entrainment, given the observed synchronization to aboveground day and night in the field (Tomotani et al, submitted). Computer simulations of an oscillator submitted to a simple model of this daily light-exposure pattern were performed using the Neurodynamix program (Friesen & Friesen, 2009). The model considers: a) one daily pulse at any time of day, restricted to daylight hours; b) fixed light intensity value, consistent with experimentally measured Phase Response Curve; c) uniform random distribution of light exposures throughout the daytime. Simulations revealed that this pattern is sufficient to entrain circadian oscillators for a broad length of day-time durations. We experimentally submitted tuco-tucos to the same light exposure model. Nine tuco-tucos were housed in individual cages with running-wheels recording the activity-rest rhythm. After free-running, they were subjected to daily light pulses (1000lux, 1h) superimposed on a dim-light background (<5lux). As an initial 30-day control, light pulses were maintained at the same time every day (LD 1:23). Thereafter, pulse time was rescheduled on each day. At first, the times of the pulses were uniformly distributed within an 8h time range for 80 days. This time range was then extended to 15h for 50 days and finally to 20h for 30 days. All animals synchronized to a 24h period under the control LD 1:23 and also under pulses distributed within 8h and 15h time-ranges. On the other hand, the 20h time-range regimen failed to impose 24h periods in 5 of the 9 tuco-tucos. The results agree with our previous simulations findings that randomly distributed daily pulses can, to some extent, work as an entraining agent and that the circadian oscillator integrates the light-phase information along several cycles. This supports the idea that the light/dark cycle may entrain the tuco-tuco’s circadian clock in the field. (CONICET, CNPq, FAPESP)