Circadian Rhythms of Body Temperature and Locomotor Activity in the Antelope Ground Squirrel, \u3cem\u3eAmmospermophilus leucurus\u3c/em\u3e

We studied circadian rhythms of body temperature and locomotor activity in antelope ground squirrels (Ammospermophilus leucurus) under laboratory conditions of a 12L:12D light-dark cycle and in constant darkness. Antelope ground squirrels are diurnally active and, exceptionally among ground squirrels and other closely related members of the squirrel family in general, they do not hibernate. Daily oscillations in body temperature consisted of a rise in temperature during the daytime activity phase of the circadian cycle and a decrease in temperature during the nighttime rest phase. The body temperature rhythms were robust (71% of maximal strength) with a daily range of oscillation of 4.6 °C, a daytime mean of 38.7 °C, and a nighttime mean of 34.1 °C (24-h overall mean 36.4 °C). The body temperature rhythm persisted in continuous darkness with a free-running period of 24.2 hours. This pattern is similar to that of hibernating species of ground squirrels but with a wave form more similar to that of non-hibernating rodents. Daily oscillations in body temperature were correlated with individual bouts of activity, but daytime temperatures were higher than nighttime temperatures even when comparing short episodes of nocturnal activity that were as intense as diurnal activity. This suggests that although muscular thermogenesis associated with locomotor activity can modify the level of body temperature, the circadian rhythm of body temperature is not simply a consequence of the circadian rhythm of activity

Diurnally Active Rodents for Laboratory Research

Although inbred domesticated strains of rats and mice serve as traditional mammalian animal models in biomedical research, the nocturnal habits of these rodents make them inappropriate for research that requires a model with human-like diurnal activity rhythms. We conducted a literature review and recorded locomotor activity data from four rodent species that are generally considered to be diurnally active, the Mongolian gerbil (Meriones unguiculatus), the degu (Octodon degus), the African (Nile) grass rat (Arvicanthis niloticus), and the antelope ground squirrel (Ammospermophilus leucurus). Our data collected under 12L:12D light-dark cycles confirmed and expanded the existing literature in showing that the activity rhythms of antelope ground squirrels and African grass rats are stronger and more concentrated in the light phase of the light-dark cycle than the activity rhythms of Mongolian gerbils and degus, making the former two species preferable and more reliable as models of consistent diurnal activity in the laboratory. Among the two more strongly diurnal species, antelope ground squirrels are more exclusively diurnal and have more robust activity rhythms than African grass rats. Although animals of these two species are not currently available from commercial suppliers, African grass rats are indigenous to a wide area across the north of Africa and thus available to researchers in the eastern hemisphere, whereas antelope ground squirrels can be found throughout much of western North America’s desert country and, therefore, are more easily accessible to North American researchers

Consumption of Shrews, Sorex spp., by Arctic Grayling, Thymallus arcticus

In an investigation of the dietary habits of Arctic Grayling (Thymallus arcticus) we found that two individuals out of 93 sampled in southwestern Alaska (approximately 59°N, 159°W) contained a total of five shrews (Sorex spp.). These shrews contained enriched levels of nitrogen stable isotopes, suggesting utilization of nutrients derived from salmon. We hypothesize that normally terrestrial shrews accidentally enter streams while foraging along the productive riparian zones of creeks with high densities of salmon. Shrews are apparently susceptible to opportunistic predation by resident stream fishes, including Arctic Grayling, when they enter the streams

Exploring Determinants of Behavioral Chronotype in a Diurnal-Rodent Model of Human Physiology

studies conducted with human participants have shown that differences in chronotype, defined as individual patterns of early or late beginning of daily activity, have implications for many biobehavioral processes, such as cognitive performance, mood, impulsivity, academic achievement of college students, and mental health. However, the determinants of individual variation in chronotype have not been investigated. Basic research on circadian rhythms has provided a basis for investigating the causes of chronotype variation, but experimental tests of pertinent hypotheses are difficult to conduct with human subjects. This limitation can be overcome by use of animal models. This study was conducted with a rodent species, the antelope ground squirrel (Ammospermophilus leucurus), that, like humans, is active during the daytime, exhibits a spread of chronotypes, and has a similar average free-running circadian period. We found chronotype to be a stable trait within individuals based on strong consistency of separate determinations made six months apart (correlation r = 0.91). We also found a moderate correlation of chronotype with the duration of the active phase (r = -0.51) and with free running period (r = 0.34), but weak correlation with rhythm robustness (r = 0.16), and no correlation with photic responsiveness or with masking responses. The best multiple regression model, incorporating the duration of the active phase, free-running period, and rhythm robustness, explained 38% of the variance in chronotype. Although 62% of the variance in chronotype remained unaccounted for, the results are encouraging because they document the possibility of using a diurnal rodent as a model for the investigation of the determinants of chronotype variation in humans

Word Retrieval Treatments for Aphasia: Connected Speech Outcomes

We examined changes in connected speech in individuals with aphasia following errorless naming treatment and gestural facilitation of naming administered in a single-participant crossover design. In addition to picture naming, participants completed two connected speech tasks during baseline and after each training phase. Positive training effect sizes in picture naming were associated with increased use of Correct Information Units and substantive nouns in connected speech. Greater use of CIUs and substantive nouns were evident for a questions task over a picture description task. Open-ended questions tended to be more effective than picture description for documenting speech changes associated with treatment

Seasonal change in the daily timing of behaviour of the common vole, Microtus arvalis

1. Seasonal effects on daily activity patterns in the common vole were established by periodic trapping in the field and continuous year round recording of running wheel and freeding activity in cages exposed to natural meteorological conditions. 2. Trapping revealed decreased nocturnality in winter as compared to summer. This was paralelled by a winter reduction in both nocturnal wheel running and feeding time in cages. 3. Frequent trap checks revealed a 2 h rhythm in daytime catches in winter, not in summer. Cage feeding activity in daytime was always organized in c. 2 h intervals, but day-to-day variations in phase blurred the rhythm in summer in a summation of individual daily records. Thus both seasonal and short-term temporal patterns are consistent between field trappings and cage feeding records. 4. Variables associated with the seasonal change in daily pattern were: reproductive state (sexually active voles more nocturnal), age (juveniles more nocturnal), temperature (cold days: less nocturnal), food (indicated by feeding experiments), habitat structure (more nocturnal in habitat with underground tunnels). 5. Minor discrepancies between field trappings and cage feeding activity can be explained by assuming increased trappability of voles in winter. Cage wheel running is not predictive of field trapping patterns and is thought to reflect behavioral motivations not associated with feeding but with other activities (e.g., exploratory, escape, interactive behaviour) undetected by current methods, including radiotelemetry and passage-counting. 6. Winter decrease in nocturnality appears to involve a reduction in nocturnal non-feeding and feeding behaviour and is interpreted primarily as an adaptation to reduce energy expenditure in adverse but socially stable winter conditions.

Negative phenotypic and genetic associations between copulation duration and longevity in male seed beetles

Reproduction can be costly and is predicted to trade-off against other characters. However, while these trade-offs are well documented for females, there has been less focus on aspects of male reproduction. Furthermore, those studies that have looked at males typically only investigate phenotypic associations, with the underlying genetics often ignored. Here, we report on phenotypic and genetic trade-offs in male reproductive effort in the seed beetle, Callosobruchus maculatus. We find that the duration of a male's first copulation is negatively associated with subsequent male survival, phenotypically and genetically. Our results are consistent with life-history theory and suggest that like females, males trade-off reproductive effort against longevity

Seasonal Patterns of Body Temperature Daily Rhythms in Group-Living Cape Ground Squirrels Xerus inauris

Organisms respond to cyclical environmental conditions by entraining their endogenous biological rhythms. Such physiological responses are expected to be substantial for species inhabiting arid environments which incur large variations in daily and seasonal ambient temperature (Ta). We measured core body temperature (Tb) daily rhythms of Cape ground squirrels Xerus inauris inhabiting an area of Kalahari grassland for six months from the Austral winter through to the summer. Squirrels inhabited two different areas: an exposed flood plain and a nearby wooded, shady area, and occurred in different social group sizes, defined by the number of individuals that shared a sleeping burrow. Of a suite of environmental variables measured, maximal daily Ta provided the greatest explanatory power for mean Tb whereas sunrise had greatest power for Tb acrophase. There were significant changes in mean Tb and Tb acrophase over time with mean Tb increasing and Tb acrophase becoming earlier as the season progressed. Squirrels also emerged from their burrows earlier and returned to them later over the measurement period. Greater increases in Tb, sometimes in excess of 5°C, were noted during the first hour post emergence, after which Tb remained relatively constant. This is consistent with observations that squirrels entered their burrows during the day to ‘offload’ heat. In addition, greater Tb amplitude values were noted in individuals inhabiting the flood plain compared with the woodland suggesting that squirrels dealt with increased environmental variability by attempting to reduce their Ta-Tb gradient. Finally, there were significant effects of age and group size on Tb with a lower and less variable Tb in younger individuals and those from larger group sizes. These data indicate that Cape ground squirrels have a labile Tb which is sensitive to a number of abiotic and biotic factors and which enables them to be active in a harsh and variable environment

Comparative gustatory responses in four species of gerbilline rodents

Integrated taste responses to chemical stimulation of the tongue were recorded from the intact chorda tympani nerve in four species of gerbils ( Meriones libycus, M. shawi, M. unguiculatus and Psammomys obesus ).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47116/1/359_2004_Article_BF00618177.pd

Insights into the pathogenesis of vein graft disease: lessons from intravascular ultrasound

The success of coronary artery bypass grafting (CABG) is limited by poor long-term graft patency. Saphenous vein is used in the vast majority of CABG operations, although 15% are occluded at one year with as many as 50% occluded at 10 years due to progressive graft atherosclerosis. Intravascular ultrasound (IVUS) has greatly increased our understanding of this process. IVUS studies have shown that early wall thickening and adaptive remodeling of vein grafts occurs within the first few weeks post implantation, with these changes stabilising in angiographically normal vein grafts after six months. Early changes predispose to later atherosclerosis with occlusive plaque detectable in vein grafts within the first year. Both expansive and constrictive remodelling is present in diseased vein grafts, where the latter contributes significantly to occlusive disease. These findings correlate closely with experimental and clinicopathological studies and help define the windows for prevention, intervention or plaque stabilisation strategies. IVUS is also the natural tool for evaluating the effectiveness of pharmacological and other treatments that may prevent or slow the progression of vein graft disease in clinical trials