http://hdl.handle.net/2027.42/56193 Search the Channel search http://deepblue.lib.umich.edu/simple-search http://hdl.handle.net/2027.42/60643 Title: Octodon degus: A diurnal, social and long-lived rodent <br/> <br/>Authors: Lee, Theresa M. <br/> <br/>Abstract: Octodon degus is a moderate-sized, precocious, but slowly maturing, hystricomorph rodent from central Chile. We have used this species to study a variety of questions about circadian rhythms in a diurnal mammal that readily adapts to most laboratory settings. In collaboration with others, we have found that a number of fundamental features of circadian function differ in this diurnal rodent compared with nocturnal rodents, specifically rats or hamsters. We have also discovered that many aspects of the circadian system are sexually dimorphic in this species. However, the sexual dimorphisms develop in the presence of pubertal hormones, and the sex differences do not appear until after gonadal puberty is complete. The developmental timing of the sex differences is much later than in the previously studied altricial, rapidly developing rat, mouse, or hamster. This developmental timing of circadian function is reminiscent of that reported for adolescent humans. In addition, we have developed a model that demonstrates how nonphotic stimuli, specifically conspecific odors, can interact with the circadian system to hasten recovery from a phase-shift of the light:dark cycle (jet lag). Interestingly, the production of the odor-based social signal and sensitivity to it are modulated by adult gonadal hormones. Data from degu circadian studies have led us to conclude that treatment of some circadian disorders in humans will likely need to be both age and gender specific. Degus will continue to be valuable research animals for resolving other questions regarding reproduction, diabetes, and cataract development. http://hdl.handle.net/2027.42/60642 Title: Estrus and steroid-induced changes in circadian rhythms in a diurnal rodent, Octodon degus <br/> <br/>Authors: Labyak, S.E.; Lee, Theresa M. <br/> <br/>Abstract: Diurnal Octodon degus exhibited marked alterations in activity and temperature in conjunction with the 3 wk estrous cycle when housed in LD12:12 light cycle. On the day of estrus, mean daily activity increases 109%, mean core temperature rises .4°C, activity onset is advanced 2 h, and amplitudes of both rhythms decline compared with the 3 days prior to estrus. On the day following estrus, activity onset was delayed 4.9 h, and mean activity and core temperature fell below that of the preestrus period. Ovariectomy significantly reduced mean temperature (.98°C) but did not significantly alter mean activity, and eliminated cyclic effects of estrus. Estrogen replacement led to a nonsignificant elevation in mean activity and core temperature with no change in the phase angle of entrainment. Progesterone replacement significantly reduced mean core temperature and mean activity, while only the phase angle difference between temperature minimum and activity onset was significantly altered. Intact degus maintained in constant darkness displayed only transient fluctuations in activity onset and temperature minimum during and after estrus. Estrogen or progesterone treatment of ovariectomized, free-running degus altered mean temperature and activity levels, but did not influence tau. Changes in phase angle of entrainment during estrus are not the result of hormone effects on the circadian clock but likely reflect increased or decreased levels of activity. http://hdl.handle.net/2027.42/60641 Title: Sex differences and effects of social cues on daily rhythms following phase advances in Octodon degus <br/> <br/>Authors: Goel, N.; Lee, Theresa M. <br/> <br/>Abstract: Two experiments were designed to determine whether social cues could enhance the rate of resynchronization in body temperature and general activity rhythms in male or female Octodon degus following a 6 h phase advance. The first experiment examined average resynchronization rates for animals in each condition. The second experiment examined resynchronization rates for a smaller group of animals, each treated as its own control. Female phase-shifters resynchronized temperature and activity rhythms significantly faster when housed with an entrained (donor) female than those females housed with another phase-shifting female or housed alone. Females housed with entrained males resynchronized their temperature rhythms significantly slower than females housed with entrained females. No differences in resynchronization rate for phase-shifting males existed between test conditions. However, activity rhythms of male controls (housed alone) reentrained significantly faster than those of female controls. These experiments demonstrate a sex difference in (i) reentrainment rate by photic cues alone; (ii) donors' effect on female phase-shifters' resynchronization; and (iii) phase-shifters' resynchronization response to donor cues. In these studies, resynchronization in the presence of another animal could either have been achieved by entrainment of the pacemaker or by masking of the circadian rhythms. http://hdl.handle.net/2027.42/60640 Title: Interaction of maternal photoperiod history and food type on growth and reproductive development of laboratory meadow voles (Microtus pennsylvanicus) <br/> <br/>Authors: Meek, L.R.; Lee, Theresa M.; Gallon, J.F. <br/> <br/>Abstract: The interaction of maternal photoperiod history and four diets were tested by measuring body growth, reproductive development, and pelage development in 9-week-old juvenile meadow voles. Meadow vole dams were housed in long daylengths (LD; 14 h light/day), short daylengths for 2 weeks (SD; 10 h light/day), or short daylengths for 26 weeks (PR; photorefractory) prior to mating. Immediately following parturition, one of four diets was available to dams and pups; (a) a control diet containing no 6-methoxy-2-benzoxazolinone (6-MBOA); (b) the control diet plus sprouted wheat (which contains 6-MBOA); (c) the control diet plus alfalfa harvested in spring (no 6-MBOA); and (d) the control diet plus alfalfa harvested in autumn (no 6-MBOA). By 9 weeks of age, juvenile meadow voles born to photorefractory dams and fed either spring or fall alfalfa or sprouted wheat were significantly larger and more had achieved puberty than juveniles fed only the control diet. Juveniles born to LD dams demonstrated a smaller increase in developmental rate than photorefractory juveniles when fed alfalfa and spring wheat, and juveniles of SD dams showed the smallest effect of alfalfa and sprouted wheat on development. Supplements of spring wheat and both forms of alfalfa had similar positive effects on growth and reproduction. The authors suggest that juvenile meadow voles rely on the interaction of maternal photoperiod history and the availability of nutrient-rich food such as sprouted wheat and alfalfa to time the onset of growth and puberty.