Housing condition alters immunological and reproductive responses to day length in Siberian hamsters (Phodopus sungorus)

During winter, increased thermoregulatory demands coincide with limited food availability necessitating physiological tradeoffs among expensive physiological processes resulting in seasonal breeding among small mammals. In the laboratory, short winter-like day lengths induce regression of the reproductive tract, but also enhance many aspects of immune function. It remains unspecified the extent to which bolstered immune responses in short days represent enhanced immune function per se compared to long days or represents energetic disinhibition mediated by the regression of the reproductive tract. Cohabitation of male Siberian hamsters with intact female conspecifics can block short-day reproductive regression. We sought to determine whether female cohabitation could also block the enhanced immune function associated with short days. Adult male Siberian hamsters were housed in long or short day lengths in one of three housing conditions: (1) single-housed, (2) housed with a same sex littermate, or (3) housed with an ovariectomized female. Delayed-type hypersensitivity (DTH) responses were assessed after 8 weeks of photoperiod treatment. Housing with an ovariectomized female was not sufficient to block short-day reproductive regression, but prevented short-day enhancement of DTH responses. Housing with a male littermate did not alter reproductive or immune responses in either photoperiod. These data suggest that short day enhancement of immune function is independent of photoperiod-mediated changes in the reproductive system.     

Androgen-dependent atypical fibromas spontaneously arising in the skin of Djungarian hamsters (Phodopus sungorus)

Spontaneous atypical fibromas that arose in the thoracoabdominal skin of one aged female and 31 aged male Djungarian hamsters (Phodopus sungorus) were examined histologically, immunohistochemically, and ultrastructurally. The normal skin from both sexes obtained at various intervals until the age of 12 months was examined, as were the tumors. These tumors were composed of ganglion cell-like (GL) cells that had one or two ovoid nuclei, basophilic foamy cytoplasm, and various amount of collagen fibers between the cells. The tumor cells had positive reaction to vimentin and androgen receptor (AR); the stromal collagen fibers reacted positively with the antibody against collagen type I or III. Ultrastructurally, the tumor cells had abundant rough endoplasmic reticulum in the cytoplasm. On the other hand, small nests of the cells mimicking tumor GL cells were present in the dermal layer to the panniculus of the normal thoracoabdominal skin of adult males, but were seldom found in adult females. The morphologic and immunohistochemical features of these tumor GL cells were basically similar to those of normal skin GL cells, although the former had a certain degree of atypia. These results suggest that atypical skin fibroma in the Djungarian hamster is an androgen-dependent tumor and originates from skin GL cells.     

Maternal transfer of photoperiodic information influences the photoperiodic response of prepubertal Djungarian hamsters (Phodopus sungorus sungorus)

Daylengths during the spring are repeated in reverse order in the autumn. For some photoperiodic species, a given photoperiod may be stimulatory for reproduction in the spring and inhibitory in the autumn. The mechanisms regulating this type of seasonal response have, until recently, remained a mystery. Horton (1984a) showed in Microtus montanus that the photoperiod experienced by the mother influences the gonadal development of her young after weaning. To determine if this phenomenon is characteristic of other photoperiodic rodents, adult Djungarian hamsters were paired on 16L:8D, 14L:10D, or 12L:12D. Young males born from these pairings were killed at 15, 28, and 34 days of age to assess gonadal development (testes weight). At 15 days testicular development was identical in all groups; by 28 days, however, males raised in 16L:8D or 14L:10D exhibited a greater degree of testicular development than those raised in 12L:12D. Next, females maintained on each of the three photoperiods throughout gestation were transferred, with their offspring, to the other two photoperiods at birth. Postnatal exposure to 14L:10D or 12L:12D inhibited testicular development in young that had been gestated on 16L:8D. Both 16L:8D and 14L:10D stimulated testicular growth in animals that had been gestated on 12L:12D or 14L:10D. Therefore, a) 16L:8D stimulates testicular growth in all animals, b) 12L:12D inhibits testicular growth in all animals, and c) the testicular response to 14L:10D depends on the photoperiod experienced by the mother during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Possible mechanisms of weight loss of Siberian hamsters (Phodopus sungorus sungorus) exposed to short photoperiod

Several weeks of short day photoperiod (SD) exposure promote a dramatic decrease of white adipose tissue (WAT) mass in Siberian hamsters(Phodopus sungorus sungorus). This slimming effect is accompanied by changes in the adipocyte responsiveness to adrenergic stimulation that are still under debate. We investigated whether possible changes in the antilipolytic responses, and/or lipogenic activities could be involved in such lipid deposition/mobilisation imbalance. Male Siberian hamsters were exposed for 11 weeks to SD or long day photoperiod and basal or stimulated lipolytic and lipogenic activities were measured on white adipocytes. As expected, the body mass of SD-animals was decreased. Besides a slight reduction in the basal lipolysis and in the maximal response to dibutyryl-cAMP, the responses to adrenergic and non-adrenergic lipolytic agents (forskolin, adenosine deaminase) were similar in both groups. Fat mass loss was likely not resulting from changes in the lipolytic responses of adipocytes to biogenic amines (e.g. octopamine), which were unaltered, or to a direct lipolytic stimulation by melatonin or histamine, which were inactive. Antilipolytic responses to insulin or tyramine were slightly decreased in SD-adipocytes. Basal or insulin-stimulated lipid accumulation in WAT, measured by glucose incorporation into lipids, did not change after SD-exposure. However, a significant decrease in the lipoprotein lipase activity was observed in the WAT of SDanimals. Despite the observed changes, the weight loss of SD-exposed Siberian hamsters was likely not resulting only from impaired antilipolytic orde novo lipogenic activities in white adipocytes, but either from other dramatic changes occurring during seasonal photoperiod-sensitive body weight regulation.     

Follicular development in immature Djungarian hamsters (Phodopus sungorus) and the influence of exogenous gonadotropins

This study evaluated follicular development and oocyte growth in ovaries of immature Djungarian hamsters from 8 to 28 days of age and examined the influence of exogenous gonadotropins on follicular growth. An age-specific pattern of progressive follicular development was found, beginning with a compact, virtually undifferentiated ovary containing mostly small follicles on Day 8 postpartum and progressing to an ovary with mature preovulatory follicles at the end of the fourth week. Antral follicles not present on Day 12 were first detected on Day 16 postpartum. Follicles were sensitive to gonadotropins (GTH) by Day 12 postpartum, as indicated by the stimulation of follicular maturation by treatment with GTH. Ovulation, however, could be induced only when treatment with GTH was begun with females from Day 14 postpartum onwards. It was concluded that the injected GTH initiated and enhanced follicular growth in immature Djungarian hamsters.     

Re-entrainment behavior of Djungarian hamsters (Phodopus sungorus) with different rhythmic phenotype following light-dark shifts

Djungarian hamsters bred at the authors' institute reveal two distinct circadian phenotypes, the wild-type (WT) and DAO type. The latter is characterized by a delayed activity-onset, probably due to a deficient mechanism for photic entrainment. Experiments with zeitgeber shifts have been performed to gain further insight into the mechanisms underlying this phenomenon. Advancing and delaying phase shifts were produced by a single lengthening or shortening of the dark (D) or light (L) time by 6?h. Motor activity was recorded by passive infrared motion detectors. All WT hamsters re-entrained following various zeitgeber shifts and nearly always in the same direction as the zeitgeber shift. On the other hand, a considerable proportion of the DAO animals failed to re-entrain and showed, instead, diurnal, arrhythmic, or free-running activity patterns. All but one of those hamsters that re-entrained did so by delaying their activity rhythm independently of the direction of the LD shift. Resynchronization occurred faster following a delayed than an advanced shift and also after changes of D rather than L. WT animals tended to re-entrain faster, particularly following a zeitgeber advance (where DAO hamsters re-entrained by an 18-h phase delay instead of a 6-h phase advance). However, the difference between phenotypes was statistically significant only with a shortening of L. To better understand re-entrainment behavior, Type VI phase-response curves (PRCs) were constructed. To do this, both WT and DAO animals were kept under LD conditions, and light pulses (15 min, 100 lux) were applied at different times of the dark span. In WT animals, activity-offset always showed phase advances, whereas activity-onset was phase delayed by light pulses applied during the first half of the dark time and not affected by light pulses applied during the second half. When the light pulse was given at the beginning of D, activity-onset responded more strongly, but light pulses given later in D produced significant changes only in activity-offset. In accord with the delayed activity-onset in DAO hamsters, no or only very weak phase-responses were observed when light pulses were given during the first hours of D. However, the second part of the PRCs was similar to that of WT hamsters, even though it was compressed to an interval of only a few hours and the shifts were smaller. Due to these differences, the first light-on or light-off following an LD shift fell into different phases of the PRC and thus caused different re-entrainment behavior. The results show that it is not only steady-state entrainment that is compromised in DAO hamsters but also their re-entrainment behavior following zeitgeber shifts.     

Peripubertal immune challenges attenuate reproductive development in male Siberian hamsters (Phodopus sungorus)

Differential allocation of energy to reproduction versus host defense is assumed to drive the seasonal antiphase relation between peak reproductive function and immunocompetence; however, evidence supporting this assumption is only correlational. These experiments tested whether photoperiod affects immune responses to antigens in peripubertal Siberian hamsters, whether such activation of the immune system exacts energetic and reproductive costs, and whether such costs vary seasonally. Male Siberian hamsters were raised from birth in long (LD) or short days (SD), which respectively initiate or inhibit the onset of puberty. To elicit a specific immune response, hamsters were injected with a novel antigen (keyhole limpet hemocyanin [KLH]) as juveniles. Reproductive development was attenuated and body temperature was elevated in LD hamsters relative to saline-injected control animals. In contrast, KLH treatments affected neither thermoregulation nor reproductive development in photoinhibited SD hamsters. In experiment 2, juvenile male hamsters were challenged with bacterial lipopolysaccharide (LPS) in order to elicit an innate immune response. Febrile and anorexic responses to LPS were greater in reproductively stimulated LD hamsters relative to reproductively inhibited SD hamsters. LPS treatments attenuated somatic and testicular development in LD hamsters, but did not significantly affect circulating testosterone concentrations. In contrast, LPS treatments were without effect on somatic and reproductive development in SD hamsters. These experiments indicate that photoperiod affects antigen-specific antibody production, febrile responses to LPS, and sickness behaviors in juvenile Siberian hamsters, and that peripubertal activation of the immune system exacts energetic and metabolic costs that can diminish the magnitude of somatic and reproductive maturation in LD. The data also underscore the importance of seasonally dependent life history factors in assessing physiological tradeoffs.     

Chromosome replication patterns in the Djungarian hamster (Phodopus sungorus)

Patterns of early and late replication in the individual chromosomes of the Djungarian hamster (Phodopus sungorus) have been studied using the techniques of Giemsa staining suppression when bromodeoxyuridine is incorporated into the DNA. — Late replicating autosome regions correspond to G-band regions, early replication regions are less clearly demarcated but correspond to R-band regions plus some G-band zones. In part this reduction in sharpness of early replication bands may be due to the fact that nearly all metaphase G-bands contain R-band material since they are compounded from blocks of sub-G bands. — The long arm of the X chromosomes in the female differ in the start time of synthesis but are rarely separable at the close of S. There are no differences between the short arms. In the male, Y starts very late but finishes about the same time as the X which behaves like the early replicating X of the female.Visiting worker from Department of Biological Sciences, Sambulpur University, Burla 768017, India     

Post-natal patterns of plasma androgen-binding activity in Djungarian (Phodopus sungorus) and golden (Mesocricetus auratus) hamsters

The binding of sex steroids to plasma proteins was examined in post-natal Djungarian and golden hamsters. With dihydrotestosterone or testosterone as ligands, steady-state polyacrylamide gel electrophoresis revealed 2 androgen binding components in the plasma of young Djungarian hamsters of both sexes. The fast-moving component exhibited a low affinity and high capacity for androgens and corresponded to albumin in stained gels. In contrast, the slow moving component was a beta-globulin with high affinity (Ka = 10(9) M-1) and low capacity for androgens, and was identified as a specific sex steroid-binding protein (SBP; also SHBG). This SBP did not bind oestrogens or corticosteroids and was electrophoretically distinct from corticosteroid-binding globulin (CBG). In addition, this protein did not appear to be of testicular origin because it was present in immature females and in immature males that had been castrated for 8 days. Plasma concentrations of SBP in males as measured by a diethyl-aminoethyl-cellulose binding assay were low at birth, became significantly elevated shortly thereafter when plasma androgen values were also elevated, and subsequently fell to low levels during puberty. These changes follow the same general pattern that has been described for other mammals, including humans, during this period of reproductive development. Although the significance of elevated SBP concentrations during prepuberty has yet to be determined, it appears that the increased concentrations of high-affinity androgen binding in the plasma of Djungarian hamsters plays a role in the asynchronous pubertal development of the testes and accessory organs which occurs in this species. The post-natal SBP pattern in females was similar to that observed in males. Plasma SBP levels were low or undetectable in adults of both sexes. As previously described for adult golden hamsters, the plasma of post-natal male and female golden hamsters lacked a specific SBP: androgen binding in this species is apparently limited to albumin and CBG.     

Maximum rates of sustained metabolic rate in cold-exposed Djungarian hamsters (Phodopus sungorus): the second wind

Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (T _as) down to −70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at T _as as high as ≥−2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation and temporal patterns of T _a changes experienced by the animals, as average T _a declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously determined and were able to maintain positive energy balances down to T _a −9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by T _as cycling between +3°C and as low as −25°C, at hourly intervals. At mean T _as between +3 and −3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body mass at lower T _as (−5 to −9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake.     

Absence of specific luteinizing hormone-releasing hormone (LHRH) receptors in the ovaries of Djungarian hamsters (Phodopus sungorus)

High affinity binding sites for luteinizing hormone-releasing hormone (LHRH) were characterized in Djungarian hamsters. Scatchard analysis was used to demonstrate specific LHRH-binding in hamster and, serving as controls, rat pituitaries (dissociation constant, KD = 0.6 nM, binding capacity, BM = 2.5 +/- 0.7 fmol/mg tissue; KD = 0.6 nM, BM = 6.9 +/- 1.9 fmol/mg tissue, respectively). In contrast to results obtained with rat ovaries (KD = 0.9 nM, BM = 3.0 +/- 0.9 fmol/mg tissue), no specific LHRH-binding was detected in hamster ovaries. Thus, it seems that direct gonadal action of LHRH in the Djungarian hamster is not involved in ovarian regulation.     

Decreased tissue guanylate cyclase activity in glycosuric Djungarian hamsters (Phodopus sungorus) that is correctable with insulin

Twelve hyperglycemic, glycosuric, and ketonuric Djungarian hamsters with average blood glucose concentrations of 295+-32 mg/dl were compared to twelve non-glycosuric, but ketonuric Djungarian hamsters with average blood glucose concentrations of 88+-11 mg/dl with regards to their cyclic nucleotide metabolism. The glycosuric Djungarian hamsters had decreased guanylate cyclase (E.C.4.6.1.2.) activity in vitro and cyclic GMP levels in vivo in liver, lung, kidney, colon, heart, spleen, and pancreas that was approximately 50% of the guanylate cyclase activity in these same tissues of non-glycosuric Djungarian hamsters. The decreased tissue guanylate cyclase activity and cyclic GMP levels in the glycosuric animals could be restored to the level of non-glycosuric Djungarian hamsters with 100 U regular insulin, but not with 50 or 10 U of regular insulin. Fifty and 100 U of regular insulin also increased the level of guanylate cyclase activity in the non-glycosuric (control) animals. There was no change in adenylate cyclase (E.C.4.6.1.1.) activity but there were increased cyclic AMP levels in the glycosuric when compared to the non-glycosuric Djungarian hamsters that were correctable with 100 U of insulin. We conclude that guanylate cyclase activity is decreased in the peripheral tissues of glycosuric Djungarian hamsters as compared to non-glycosuric Djungarian hamsters and that insulin modulates this enzyme.     

Photoperiod and food restriction differentially affect reproductive and immune responses in Siberian hamsters Phodopus sungorus

1.  Organisms must contend with seasonal fluctuations in energy availability. To maintain a positive energy balance year-round, a number of adaptations have evolved including seasonal changes in reproduction, energetics and immunity. Photoperiod is the primary environmental signal most animals use to predict seasonal events. Despite the established link between energetics and immune function, little is known regarding how changes in energy availability affect immunity.
2.  The goal of the present study was to determine the effects of food restriction on photoperiodic changes in reproduction and immune function in the Siberian hamster ( Phodopus sungorus ). Adult hamsters were housed in long or short days and were food restricted or fed ad libitum . Immune responses were quantified by measuring specific antibody production and bacterial killing capacity.
3.  Food restriction decreased body and relative reproductive masses in long-day animals. Antibody responses, but not bacterial killing ability, were enhanced in food restricted short-day animals as compared with ad libitum fed controls. We also found differential effects of body fat on immune responses depending on the immune measure.
4.  The effects of food restriction on immune function appear to vary based on the restriction regimen, the response measured, and the physiological state of the organism including energy balance, metabolic rate and reproductive status.
5.  In conclusion, these results suggest that a wide range of factors can differentially affect immune function. In addition, these effects may vary based on the specific response examined. Future studies should include a variety of measurements to provide a more integrative and accurate picture of reproductive, energetic, and photoperiodic effects on immune function.     

Social cues attenuate photoresponsiveness of the male reproductive system in Siberian hamsters (Phodopus sungorus)

Transfer of adult Siberian hamsters (Phodopus sungorus) from long (16 h light and 8 h dark, 16L:8D) to short (8L:16D) daily photoperiods induces an involution of the gonads and a cessation of reproductive behavior 8 to 10 weeks later. However, when male and female long-day hamsters were paired on transfer to short photoperiods, the males' gonads did not undergo the typical short-day response. Similarly, when male long-day hamsters were paired with refractory females (i.e., females housed in short photoperiods for at least 28 weeks so that they became unresponsive to short photoperiods), the response of the males' reproductive system to short photoperiods also was attenuated. Thus, social cues can override or delay the effects of photoperiod on the testes of this species. These results suggest that the inhibitory effects of long durations of melatonin secretion (in response to short photoperiods) on the male hypothalamic-pituitary-gonadal axis may be attenuated by social cues such as contact with the opposite sex.     

Cardiac dynamics during daily torpor in the Djungarian hamster (Phodopus sungorus)

Djungarian or Siberian hamsters (Phodopus sungorus) acclimated to short photoperiod display episodes of spontaneous daily torpor with metabolic rate depressed by approximately 70% and body temperature (T(b)) reduced by approximately 20 degrees C. To study the cardiovascular adjustment to daily torpor in Phodopus, electrocardiogram (ECG) and T(b) were continuously recorded by telemetry during entrance into torpor, in deep torpor, and during arousal from torpor. Minimum T(b) during torpor bouts was approximately 21 degrees C, and heart rate, approximately 349 beats/min at euthermy, displayed marked sinus bradyarrhythmia at approximately 70 beats/min. Arousal was typically completed within approximately 40 min, followed by a sustained post-torpor inactivity tachycardia ( approximately 540 beats/min). The absence of episodes of conduction block, tachyarrhythmia, or other forms of ectopy throughout the torpor cycle demonstrates a remarkable resistance to arrhythmogenesis. The ECG morphology lacks a distinct isoelectric interval following the QRS complex, and the ST segment resembles the ECG pattern in mice, with a prominent fast transient outward K(+) current (I(to,f)) determining the early phase of ventricular repolarization. During low-temperature torpor, the amplitudes of the QRS complex substantially increased, suggesting that in the euthermic state the terminal portion of ventricular depolarization is fused with the beginning of repolarization, low T(b) acting to decorrelate the superposition between depolarization and repolarization by delaying the repolarization onset. Atrioventricular and ventricular conduction times were prolonged as function of T(b). In contrast, the QT vs. T(b) relationship showed marked hysteresis indicating the operation of nonlinear control mechanisms whereby the rapid QT shortening during arousal results from additional mechanisms (probably sympathetic stimulation) other than temperature alone.     

Metabolism and thermoregulation in two races of Djungarian hamsters: Phodopus sungorus sungorus and P. s. campbelli

Two races of Djungarian hamsters (Phodopus sungorus sungorus and P. s. campbelli) differ in their responses to low ambient temperatures. The lowest temperature tolerated is 6-10 degrees C higher in P. s. campbelli than in P. s. sungorus, both in summer and in winter, but the highest (Vo2-max) and lowest (BMR) metabolic rates are similar in both subspecies. Body temperature and overall conductance in the cold appear to be more variable in P. s. campbelli than in nominative sp.     

The role of ozone/oxygen in clindamycin-associated enterocolitis in the Djungarian hamster (Phodopus sungorus sungorus)

Rectal and oral ozone-O2 gas insufflations prevented a fatal clindamycin-induced enterocolitis in Djungarian dwarf hamsters. In spite of no gross lesions in the colon of these species, the term 'colitis' is justified because of intracellular degenerative changes of colon epithelial cells. Dwarf hamsters are omnivores and are, therefore, more relevant to man than other animal species as an animal model for studying colitis.     

Nucleolus-like bodies in the pineal gland of the Djungarian hamster (Phodopus sungorus)

Summary Light- and electron-microscopic observations on the pineal gland of Phodopus sungorus revealed intracytoplasmic inclusions resembling nucleolus-like bodies similar to those found in other regions of the central nervous system. Bernhard's EDTA method was used to confirm that these inclusions were nucleolus-like bodies. These structures were rarely found in pinealocytes of sexually active longday animals, whereas large numbers of them were observed in pinealocytes of sexually quiescent short-day animals. Nucleolus-like bodies may therefore be involved in pineal secretion.     

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli).

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.