The objective of this project is to investigate circadian rhythm biology in naked mole-rats. Naked mole-rats are highly social rodents that live in large colonies (60-80 individuals). They are among the most exclusively subterranean of mammals; many individuals may never leave their underground burrows. Circadian (daily) rhythms of locomotor activity, body temperature, and metabolic rate will be examined to determine whether mole-rats, like more 'typical' mammals exhibit rhythmic daily variations that are regulated by an internal biological clock. The project will also examine whether mole-rat rhythms (and the clock that controls them) are influenced by light, as is the case for other organisms. Finally, the possibility of influence of circadian rhythms by social interactions will also be examined in mole-rat colonies. Rhythms of locomotor activity will be studied by continuous monitoring of activity of individuals both within a colony setting and when animals are isolated from their colonies. Body temperature variations will be measured by use of implanted telemeters, and metabolic rate will be assessed by continuous measurements of oxygen consumption.
In all organisms that have been carefully studied, the biological clocks that regulate circadian rhythms are synchronized primarily by light cues, but there is evidence that under certain circumstances these clocks can also be synchronized by social cues. Yet, the most intensely studied species (rats, mice, hamsters) are relatively non-social, and few studies have been performed with social mammals. Humans clearly organize many of their daily activities in relation to social interactions, and in its most extreme form this extends to areas such as shift work and non-24 hour work schedules in certain situations. Despite some research in these areas---particularly with regard to sleep/wake rhythms, body temperature rhythms, and rhythms of hormone secretion---it is not clear how the human circadian system is involved in social aspects of human daily rhythms. By examining a mammal recently discovered to have evolved an unusually high degree of social organization, it will be possible to assess the potential of the mammalian circadian system for functioning in the context of social cues. This will provide valuable cues in the effort to understand the human circadian system. In addition to their extreme sociality, naked mole-rats live in burrows where they are very rarely exposed to light and may thus be unable to make use of the light:dark cycle for synchronization of biological rhythms. Naked mole-rats are also relatively unique in exhibiting a very low body temperature and metabolic rate as compared to other mammals. Therefore, studies of the circadian regulation of metabolism and body temperature in naked mole-rats will extend our understanding of the physiology of mammalian energetics.
