Title

Circadian rhythms of locomotor activity, metabolic rate, and body temperature in the fossorial and eusocial naked mole-rat (Heterocephalus glaber): A behavioral and neuroanatomical study of the circadian system

Date of Completion

January 1999

Keywords

Biology, Anatomy|Psychology, Behavioral|Biology, Animal Physiology|Biology, Zoology

Degree

Ph.D.

Abstract

Circadian rhythms are biological rhythms that are evident in virtually all eukaryotic organisms. Mammals synchronize their behavioral and physiological circadian rhythms to environmental cues such as the light:dark (L:D) cycle. This allows mammals to anticipate and prepare for predictable environmental events such as night, winter, or reproductive function in potential mates. There have been few studies of circadian rhythms in subterranean animals, which are infrequently exposed to light and experience minimal day:night differences. Naked mole-rats are a fossorial and eusocial species that live in hot and arid parts of Africa. They live in colonies averaging 70 animals and maintain integrity of the colony with the presence of a social caste system, which includes few reproductive individuals, defenders, workers, and foragers. This animal would be a model for the study of circadian rhythms in a subterranean species as well as a highly social animal. This thesis presents a group of experiments that demonstrate the existence of a functional circadian system in the naked mole-rat. We demonstrated that approximately 66% of the mole-rats studied exhibit robust circadian rhythms of locomotor activity, metabolic rate, and body temperature, all of which are highly correlated. These behavioral and physiological rhythms have the ability to entrain to varying L:D cycles and freerun in constant darkness (DD). We also demonstrated the presence of the suprachiasmatic nucleus of the hypothalamus (SCN), the nucleus found to be the location of the endogenous rhythm generator. This was demonstrated using a retina neuronal tracing method. We observed direct innervation of retinal fibers in the SCN. Therefore, in its entirety, this study has made a critical contribution to the biological rhythm literature with information on the functional capacity of the circadian system in a subterranean species that is rarely exposed to light and that is highly social. It also provides a thorough investigation of the circadian system of a fossorial mammal that can be used for comparative studies with other fossorial and above ground rodents. ^