Splitting of the circadian rhythms of body temperature and locomotor activity in the tuco-tuco (Ctenomys aff. knighti), a South-American subterranean rodent

TACHINARDI P; ODA GA; VALENTINUZZI VS

Florida

Congreso; Society for Research in Biological Rhythms- SRBR; 2012

SRBR

Splitting of circadian motor activity rhythms is observed in several species under constant light (LL) conditions. Although it has been more thoroughly studied in model animals, splitting occurs in wild species in the laboratory, some of which live in extreme environments, e.g., in arctic ground squirrels (Swade and Pittendrigh, 1967 ), which naturally face LL during part of the year. Living in almost opposite lighting conditions, the South American subterranean tuco-tucos (Ctenomys knighti), which face constant darkness inside their tunnels and are only exposed to light during brief aboveground excursions, also display splitting of the motor activity rhythm, showing a remarkable wide repertoire of rhythmic patterns under LL.  This fact prompted us to investigate whether this same variability in splitting patterns is also displayed by the tuco-tuco?s body temperature (Tb) rhythm. Such study would also allow us to test whether activity and Tb rhythms are controlled by the same circadian oscillators, using neurally intact animals. Because splitting occurs due to the dynamical dissociation of two oscillators located in the SCN, it was hypothesized that if these oscillators control both activity and Tb rhythms, they would show identical patterns under LL. To address this issue, we measured Tb, gross motor activity and wheel running in nine wild-caught tuco-tucos from Northwest Argentina. These animals, previously entrained to a light-dark (LD) cycle (12:12), were exposed to LL (200-300 lux) for 125-145 days and then reentrained to the LD cycle. In order to filter the masking effects of muscular locomotor activity in the increase of Tb we treated the data using the method developed by Weinert and Waterhouse (1998), which takes into account that the sensibility of Tb to muscular activity is dependent on the phase of the day. In seven tuco-tucos both Tb and motor activity rhythms split, with remarkable variability in splitting patterns. In six of them, Tb and motor activity showed exactly the same patterns, whereas in one the Tb rhythm displayed an extra component. These results suggest that activity and Tb rhythms are controlled by the same two circadian oscillators that dissociate under splitting. However, the emergence of extra components indicates that this control might be more complex.