Seasonal changes of heart weight and erythrocytes in the Djungarian hamster, Phodopus sungorus

Biology and Diseases of Hamsters

The hamster species used as research models include the Syrian (golden), Mesocricetus auratus; the Chinese (striped-back), Cricetulus griseus; the Armenian (gray), C. migratorius; the European, Cricetus cricetus; and the Djungarian, Phodopus campbelli (Russian dwarf) and P. sungorus (Siberian dwarf). Hamsters are classified as members of the order Rodentia, suborder Myomorpha, superfamily Muroidea and in family Cricetidae. Animals in this family are characterized by large cheek pouches, thick bodies, short tails, and an excess of loose skin. They have incisors that erupt continuously and cuspidate molars that do not continue to grow ((I 1/1, C 0/0, PM 0/0, M 3/3) × 2 = 16). In 2010, it was reported that approximately 146,000 hamsters were used in research in the United States (United States Department of Agriculture, 2010).

Variation in hematologic and serum biochemical values of belugas (Delphinapterus leucas) under managed care

Blood analytes are critical for evaluating the general health of cetacean populations, so it is important to understand the intrinsic variability of hematology and serum chemistry values. Previous studies have reported data for follow-up periods of several years in managed and wild populations, but studies over long periods of time (> 20 yr) have not been reported. The study objective was to identify the influences of partitioning characteristics on hematology and serum chemistry analytes of apparently healthy managed beluga (Delphinapterus leucas). Blood values from 31 managed belugas, at three facilities, collected over 22 yr, were assessed for seasonal variation and aging trends, and evaluated for biologic variation among and within individuals. Linear mixed effects models assessed the relationship between the analytes and sex, age, season, facility location, ambient air temperature, and photoperiod. Sex differences in analytes and associations with increasing age were observed. Seasonal variation was observed for hemoglobin, hematocrit, mean corpuscular volume, monocytes, alkaline phosphatase, total bilirubin, cholesterol, and triglycerides. Facilities were associated with larger effects on analyte values compared to other covariates, whereas age, sex, and ambient temperature had smaller effects compared to facility and season. Present findings provide important baseline information for future health monitoring efforts. Interpretation of blood analytes and animal health in managed and wild populations over time is aided by having available typical levels for the species and reference intervals for the degree to which individual animals vary from the species average and from their own baseline levels during long-term monitoring.

Influence of season on the hematological and serum biochemical values of bottlenose dolphins (Tursiops truncatus) housed in a controlled environment in northern Italy

Season appears to influence the physiology of bottlenose dolphins (Tursiops truncatus). From 2000 to 2005, blood parameters of three captive bottlenose dolphins housed in northern Italy were examined to determine if seasonal variation was present. Seasonal variation was observed in the male dolphins, with both males exhibiting aminotransferase levels that were higher in autumn and lower in winter. Mean serum creatinine levels were higher during summer and lower during autumn in the adult male, and mean lactate dehydrogenase higher during summer and lower during spring in the juvenile male. Both males exhibited red blood cell counts and hemoglobin levels that were higher during autumn and lower during summer. This study contributes to the knowledge of baseline hematologic and biochemical values based on seasonality in bottlenose dolphins.

Thermal acclimation and seasonal variations of erythrocyte size in the Andean mouse Phyllotis xanthopygus rupestris

Seasonal hematological adjustments in small mammals may include changes in the number and size of the red cells or changes in other linked blood parameters. The direction and magnitude of these changes vary in different species. We hypothesized that the observed variations of the red cell adjustments could be directly related to the magnitude of the seasonal temperature differential, and predicted that the annual red cell size variation in rodents from environments with marked seasonal changes would tend to disappear, if the animals were raised under milder and constant environments. To test this idea, we got field blood samples from the Andean species Phyllotis xanthopygus rupestris enduring a winter-summer thermal differential of at least 20 degrees C. These animals had significantly smaller erythrocytes during the winter. Contrary to our prediction, their offspring born and raised under constant temperature conditions showed a similar trend. Unless the effective environmental cue differed from the one we used, these results favor the idea of a genetically determined annual red cell size variation that occurs independent of thermal acclimation and acclimatization.

Photoperiod differentially regulates circadian oscillators in central and peripheral tissues of the Syrian hamster

In many seasonally breeding rodents, reproduction and metabolism are activated by long summer days (LD) and inhibited by short winter days (SD). After several months of SD, animals become refractory to this inhibitory photoperiod and spontaneously revert to LD-like physiology. The suprachiasmatic nuclei (SCN) house the primary circadian oscillator in mammals. Seasonal changes in photic input to this structure control many annual physiological rhythms via SCN-regulated pineal melatonin secretion, which provides an internal endocrine signal representing photoperiod. We compared LD- and SD-housed animals and show that the waveform of SCN expression for three circadian clock genes (Per1, Per2, and Cry2) is modified by photoperiod. In SD-refractory (SD-R) animals, SCN and melatonin rhythms remain locked to SD, reflecting ambient photoperiod, despite LD-like physiology. In peripheral oscillators, Per1 and Dbp rhythms are also modified by photoperiod but, in contrast to the SCN, revert to LD-like, high-amplitude rhythms in SD-R animals. Our data suggest that circadian oscillators in peripheral organs participate in photoperiodic time measurement in seasonal mammals; however, circadian oscillators operate differently in the SCN. The clear dissociation between SCN and peripheral oscillators in refractory animals implicates intermediate factor(s), not directly driven by the SCN or melatonin, in entrainment of peripheral clocks.

Photoperiodic adjustments in immune function protect Siberian hamsters from lethal endotoxemia

Seasonal changes in day length enhance or suppress components of immune function in individuals of several mammalian species. Siberian hamsters (Phodopus sungorus) exhibit multiple changes in neuroendocrine, reproductive, and immune function after exposure to short days. The manner in which these changes are integrated into the host response to pathogens is not well understood. The present experiments tested the hypothesis that short-day changes in immune function alter the pathogenesis of septic shock and survival after challenge with endotoxin. Male and female Siberian hamsters raised in long-day photoperiods were transferred as adults to short days or remained in their natal photoperiod. Six to 8 weeks later, hamsters were injected i.p. with 0, 1, 2.5, 10, 25, or 50 mg/kg bacterial lipopolysaccharide (LPS) (the biologically active constituent of endotoxin), and survival was monitored for 96 h. Short days significantly improved survival of male hamsters treated with 10 or 25 mg/kg LPS and improved survival in females treated with 50 mg/kg LPS. Transfer from long to short days shifted the LD50 in males by approximately 90%, from 5.3 to 9.9 mg/kg, and in females from 11.1 to 15.0 mg/kg (+35%). Long-day females were more resistant than were males to lethal endotoxemia. In vitro production of the proinflammatory cytokine TNFalpha in response to LPS stimulation was significantly lower in macrophages extracted from short-day relative to long-day hamsters, as were circulating concentrations of TNFalpha in vivo after i.p. administration of LPS, suggesting that diminished cytokine responses to LPS in short days may mitigate the lethality of endotoxemia. Adaptation to short days induces changes in immune parameters that affect survival in the face of immune challenges.

Seasonal changes of blood values in the Andean mouse Abrothrix andinus

1. Biomonthly measurements of hematological indices were conducted in freshly captured Abrothrix andinus (Rodentia:Cricetidae) over a period of one year. 2. All blood values were in the same range for adult males and females, but juveniles showed lower red blood cell counts (RBC) and erythrocytes of larger size. 3. High RBC numbers, a slight but significant increase of blood hemoglobin concentration (Hb), and a significant decrease in mean cell volume (MCV) were found during the winter months. 4. Hematocrit values (Hct) and the mean cell Hb concentration (MCHC) were relatively constant throughout the year. 5. Plasticity of MCV and an inverse correlation between size and the number of RBC may provide an enlarged diffusion area during winter. This mechanism appears to be a useful seasonal adjustment, since the increase of Hct and the concurrent increase in blood viscosity are avoided.

Seasonal changes in blood parameters in the bat species Rhinolophus ferrumequinum and miniopterus schreibersi

Intersexual and seasonal comparisons of erythrocyte number, hematocrit, and hemoglobin concentration were conducted for two old world temperate bats, Rhinolophus ferrumequinum and Miniopterus schreibersi. Both species had many small erythrocytes and elevated hemoglobin concentrations. Seasonal differences in erythrocyte count, hemoglobin concentration, and mean cell volume were found in each species. The increase in the number of small erythrocytes in the warm season may be related to heightened activity of the bats during this period. High blood-oxygen capacities associated with high hemoglobin concentrations and hematocrit values increase oxygen delivery to tissues in species with small body size and high metabolic rates.

Hematological data and hemoglobin components in bats (Vespertilionidae)

1. Statistically significant variations were observed in the RBC counts and Hb concentration in pregnant females of Pipistrellus pipistrellus. 2. Basic hematological values in 59 animals of five species of insectivorous bats were estimated. 3. Electrophoretic separation of the hemoglobins of Plecotus austriacus, Myotis nattereri and Myotis myotis showed two components, whereas in Miniopterus schreibersi and Pipistrellus pipistrellus appeared three and four components, respectively.