Browsing by Subject "Body temperature rhythm"

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    Behavioral and thermoregulatory responses to changes in ambient temperature and wheel running availability in Octodon degus
    (Frontiers Media, 2021-06-30) Bano Otalora, Beatriz; Rol de Lama, María de los Ángeles; Madrid, Juan Antonio; Fisiología
    Octodon degus is primarily a diurnal species, however, in laboratory conditions, it can switch from diurnal to nocturnal in response to wheel running availability. It has been proposed that this activity inversion obeys thermoregulatory constraints induced by vigorous physical exercise. Thus, its activity shifts to the night as the ambient temperature is lower.Here, we investigate the relationship between thermoregulation and the activity phase-inversion in response to wheel-running in this species. We measured behavioral activity and body temperature rhythms in diurnal naïve animals under 12 h light: 12 h dark cycles at four different ambient temperatures (spanning from ~26°C to 32°C), and following access to running wheels while maintained under high ambient temperature.Our results show that naïve degus do not shift their diurnal activity and body temperature rhythms to a nocturnal phase when subjected to sequential increases in ambient temperature. However, when they were provided with wheels under constant high-temperature conditions, all animals inverted their diurnal phase preference becoming nocturnal. Both, negative masking by light and entrainment to the dark phase appeared involved in the nocturnalism of these animals. Analysis of the thermoregulatory response to wheel running revealed some differences between masked and entrained nocturnal chronotypes.These data highlight the importance of the coupling between wheel running availability and ambient temperature in the nocturnalism of the degus. The results support the view that an innate “protective” pre-program mechanism (associating darkness and lower ambient temperature) may change the timing of behavioral activity in this species to reduce the potential risk of hyperthermia.
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    Circadian system functionality, hippocampal oxidative stress, and spatial memory in the APPswe/PS1dE9 transgenic model of Alzheimer disease: effects of melatonin or ramelteon
    (Taylor and Francis Group, Taylor and Francis, 2012-07-23) Baño-Otalora, Beatriz; Gambini, Juan; Viña, José; Bonet-Costa, Vicent; Reiter, Russel J.; Camello, Pedro Javier; Rol, María Ángeles; Madrid, Juan Antonio; Popovic, Natalija; Popovic Popovic, Miroljub; Anatomía Humana y Psicobiología
    Alzheimer disease (AD) is a neurodegenerative disorder that primarily causes β-amyloid accumulation in the brain, resulting in cognitive and behavioral deficits. AD patients, however, also suffer from severe circadian rhythm disruptions, and the underlying causes are still not fully known. Patients with AD show reduced systemic melatonin levels. This may contribute to their symptoms, since melatonin is an effective chronobiotic and antioxidant with neuroprotective properties. Here, the authors critically assessed the effects of long-term melatonin treatment on circadian system function, hippocampal oxidative stress, and spatial memory performance in the APPswe/PS1 double transgenic (Tg) mouse model of AD. To test if melatonin MT1/MT2 receptor activation, alone, was involved, the authors chronically treated some mice with the selective MT1/MT2 receptor agonist ramelteon. The results indicate that many of the circadian and behavioral parameters measured, including oxidative stress markers, were not significantly affected in these AD mice. During the day, though, Tg controls (Tg-CON) showed significantly higher mean activity and body temperature (BT) than wild-type (WT) mice. Overall, BT rhythm amplitude was significantly lower in Tg than in WT mice. Although melatonin treatment had no effect, ramelteon significantly reduced the amplitude of the BT rhythm in Tg mice. Towards the end of the experiment, Tg mice treated with ramelteon (Tg-RAM) showed significantly higher circadian rhythm fragmentation than Tg-CON and reduced circadian BT rhythm strength. The free-running period (τ) for the BT and locomotor activity (LA) rhythms of Tg-CON was <24 h. Whereas melatonin maintained τ at 24 h for BT and LA in both genotypes, ramelteon treatment had no effect. In the behavioral tests, the number of approaches and time spent exploring novel objects were significantly higher in Tg-CON than WT controls. Brain tissue analysis revealed significant reduction in hippocampal protein oxidation in Tg-MEL and Tg-RAM compared with Tg-CON animals. These results suggest that not all aspects of the circadian system are affected in the APPswe/PS1 mice. Therefore, care should be taken when extending the results obtained in Tg mice to develop new therapies in humans. This study also revealed the complexity in the therapeutic actions of melatonin and ramelteon in this mouse model of AD.