Sincronização fótica de um roedor subterrâneo: um estudo cronobiológico de campo e de laboratório do tuco-tuco (Ctenomys cf. knighti)

Abstract

Agradecimentos Meus pais, pelo apoio em todos os sentidos, durante esses três anos de Mestrado. Gisele Akemi Oda, minha orientadora brasileira, e Verónica Sandra Valentinuzzi, minha orientadora na Argentina (cuja orientação infelizmente não pôde ser oficializada por questões burocráticas). Barbara Tomotani e Patricia Tachinardi, colegas de laboratório, que me suportaram durante as longas estadias em Anillaco, e participaram ativamente no planejamento, execução, análise e discussão de todos os experimentos de campo e laboratório. Mirian Marques, que, juntamente com minha orientadora Gisele Oda, me introduziu ao mundo da Cronobiologia e me mostrou o que é fazer uma boa ciência. José Paliza, que construiu a maior parte dos equipamentos de laboratório e campo, e garantiu que nossas idéias saíssem do papel. Funcionários e Pesquisadores do CRILAR, por tornarem minha estadia em Anillaco uma experiência prazerosa e contribuírem com discussões frutíferas. AbstractDaily rhythms are found in the biological variables of many organisms, in parallel to the environmental day and night. Most of those rhythms are not mere reactions to the cyclic stimulus of the environment. They are actually circadian rhythms, endogenously generated by an internal timer, the circadian oscillator, which sustains a non-24-hour rhythm under constant conditions, but is synchronized to a 24-hour period when exposed do a cyclic environment. In mammals, this oscillator is located in the brain, and can be synchronized by the daily light-dark cycle (LD cycle) of day and night. Subterranean animals remain most of the time in an underground habitat, where environmental conditions vary less markedly than aboveground.Therefore, there are doubts whether these animals maintain circadian rhythms and whether their circadian oscillators rely on the LD cycle for environmental synchronization. We attempted to answer those questions in subterranean rodents of the species Ctenomys cf.knighti (tuco-tucos). In the field, we performed direct visual observations to assess their temporal pattern of light-exposure. In the lab, we build the Phase Response Curve (PRC), which consists in an indirect measurement of the circadian oscillator responses to light stimuli applied at different times of the day. Finally, computer simulations of an oscillator model were used to integrate these previous data. We verified that tuco-tucos expose themselves to light pulses that are irregularly distributed through day-light hours, raising some questions about its validity as an environmental synchronizer. However, the PRC results indicated that the tucotucos circadian system responds to light stimuli in a way similar to non-subterranean animals.We then verified three hypothesis: either the light-exposure temporal information was enough for the synchronization of the circadian system, despite its apparent irregularity; or the tucotuco's PRC present some feature that facilitates the synchronization by the observed lightexposure regimen; or the tuco-tuco's circadian system rely on anoth...

Sincronização fótica e não fótica dos ritmos circadianos em roedores subterrâneos (Ctenomys aff. knighti) e roedores modelo de laboratório (Mus musculus)

“…The model had already been shown to synchronize the rhythms of a mathematical oscillator in computer simulations (Flôres, 2011;Flôres et al, 2013). Our experimental data confirmed the predictions from the simulations: light pulses applied once a day at varying random times ( Figure 5.1D bottom) can still act as a zeitgeber.…”

“…Contrary to our expectations, however, the mathematical oscillator was in fact entrained to a 24-hour period in response to the minimal model of light exposure ( Figure 2.1.3C), with distribution intervals I as wide as 14 hours. This finding was replicated with three different parameter configurations of the mathematical oscillator (Flôres, 2011).…”

“…Double plotting makes it easier to follow free-running rhythms in constant conditions, with periods different from 24 hours. Modified from (Flôres, 2011).…”

“…An initial device (Insight Equipamentos, Pesquisa e Ensino; Ribeirão Preto, SP, Brazil) (Figure 2.1.1A) was built to measure both activity and light exposure continuously, but there was a crosstalk between the two measurements and the size of the device was an issue (Flôres, 2011). The second and third devices (Ecotone; Gdynia, Poland) (Figure 2.1.1B, C) were fairly smaller and the third device was thoroughly tested in the laboratory and once in the field.…”

“…We began to answer this question during my master's work, using computer simulations of a mathematical circadian oscillator of the limit-cycle type, subjected to different virtual light regimens (Flôres, 2011;Flôres et al, 2013). As a common approach to mathematical modelling studies, we devised a simplified version of light exposure that would capture the critical aspects of the particular light regimen experienced by tucotucos in the field.…”