Photic and non-photic synchronization of the circadian rhythms in subterranean rodents (Ctenomys aff. knighti) and laboratory model rodents (Mus musculus)

Author(s)

Danilo Eugênio de França Laurindo Flôres

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2016-10-03

Examining board members

Gisele Akemi Oda; José Eduardo de Carvalho; Ana Maria de Lauro Castrucci; Paula Ayako Tiba

• Advisor: Gisele Akemi Oda; Verônica Sandra Valentinuzzi

Abstract

Our research group studies circadian rhythms in a subterranean rodent from the genus Ctenomys, the tuco-tuco. In this thesis, I will present data on photic and non-photic synchronization of circadian rhythms in tuco-tucos, as well as a study on non-photic synchronization in the laboratory mouse. Natural photic synchronization in tuco-tucos was verified with field and laboratory approaches. We initially measured the natural light/dark cycle experienced by tuco-tucos in semi natural field enclosures, by means of automatic light logger devices that continuously recorded the daily temporal pattern of light exposure. Next, a model of this light exposure pattern was applied to tuco-tucos in the laboratory, to test its potential as a photic synchronizer of the circadian rhythms. The model consisted of single light pulses applied once a day at varying random times. Despite the minimal timing information, this light regimen was a successful synchronizer in many instances, as predicted from previous computer simulations of a mathematical oscillator. These results revealed that the synchronization of circadian oscillators is even more robust than previously thought. Our second set of experiments evaluated the non-photic synchronization in the herbivorous tuco-tucos, by exposing animals to daily cycles of food availability. Similar to other rodent species, tuco-tucos in this protocol developed a circadian food anticipatory activity (FAA) right before the daily feeding time. However, there was great interindividual variability in FAA expression, likely related to differences in the metabolic responses to time-restricted feeding. The final work was a collaboration with Dr. Shin Yamazaki from the University of Texas Southwestern Medical Center, regarding non-photic synchronization in wildtype and mutant mice with genetic disruption of the circadian clock. Daily cycles of palatable food and wheel running induced self-sustaining rhythmicity in arrhythmic mutant mice, which do not express the Period genes, key components of the molecular machinery responsible for circadian rhythm generation within the cells. These results suggest the existence of novel circadian oscillators responsive to daily rewarding signals. While model laboratory species such as the mouse can bring valuable information on physiological mechanisms, wild species like the tuco-tuco can give us insights into the ecological meaning of circadian phenomena (AU)

• FAPESP's process: 11/24120-0 - A lab, field and computer study of the synchronization of circadian rhythms in the subterranean rodent tuco-tuco (Ctenomys aff. knighti)
• Grantee: Danilo Eugênio de França Laurindo Flôres
• Support Opportunities: Scholarships in Brazil - Doctorate