Development of Species Preferences in Two Hamsters, Phodopus campbelli and Phodopus sungorus: Effects of Cross-Fostering

Experiments were conducted to investigate species-specific preferences in two closely related species of hamsters, Phodopus campbelli and Phodopus sungorus . Male hamsters that were raised with conspecifics spent more time investigating an anaesthetized conspecific male than a heterospecific male, and also spent more time investigating odours of conspecifics than those of heterospecifics (midventral gland, urine, and saccular secretion). Cross-fostered P. sungorus males reversed their normal preferences, spending more time investigating stimuli (anaesthetized males and all three odours) of the foster species. Cross-fostered P. campbelli males also investigated an anaesthetized male of the foster species more than a male of their own species, but did not show a preference for odours alone. Social experience during the 15 d immediately following weaning also influenced these preferences. If exposures during and after nesting were to heterospecifics the preference for heterospecifics was strengthened; if either period of experience was with a conspecific, this eliminated the preference for heterospecifics in P. sungorus but did not influence the lack of a preference in P. campbelli . Thus, early experience during both the nestling stage and the 15 d after weaning influenced responses to species-typical cues in both species, but it had a more pronounced effect in P. sungorus .     

Characteristics of the first meiotic division in hamster hybrids obtained by backcrossing Phodopus sungorus and Phodopus campbelli]

Spermatocytes of fertile, subfertile, and sterile hamster hybrids obtained by backcrossing Phodopus sungorus and Ph. campbelli were analyzed under light and electron microscopes. Light microscopy showed that early meiosis was blocked in pachitene in the spermatocytes of sterile hybrids. The X and Y chromosomes were dissociated in metaphase I in several fertile and subfertile animals. Electron microscopic analysis of the synaptonemal complex (SC) revealed a disturbed synapsis of sex chromosomes and autosomes in all hybrids. Dissociation of the sex chromosomes, terminal and interstitial asynapsis, and interlocking of autosomes were observed. Disturbed synapsis in hybrids was assumed to result from the difference between Ph. sungorus and Ph. campbelli in not only their chromosomes, but their genes as well.     

Hormonal changes in males of a naturally biparental and a uniparental mammal

Blood samples from male hamsters (Phodopus) during their mate's gestation and early lactation show that key hormones important in maternal behavior are also changing in males and differ for two closely related species with different levels of paternal care. Results of study 1 were consistent with a relationship between higher prolactin, lower testosterone and paternal behavior during early lactation in P. campbelli and provided no evidence for similar hormonal changes in P. sungorus. Study 2 sampled males before or after the birth. Prolactin did not increase until at least one day after the birth in P. campbelli but was high at the end of the pregnancy in P. sungorus. Increasing testosterone concentrations in P. campbelli as the birth approached were consistent with mate guarding, high testosterone concentrations on L5 were consistent with paternal aggression in defense of the litter, and the drop in testosterone after the birth was consistent with reduced aggression toward the new pups. Results confirmed that cortisol concentrations were reduced following the establishment of a pair-bond and found that P. campbelli males had elevated cortisol before the birth. Results support the hypothesis that mammalian paternal behavior has a hormonal basis which is analogous to maternal behavior.     

Estradiol and progesterone in paternal and non-paternal hamsters (Phodopus) becoming fathers: conflict with hypothesized roles

Phodopus campbelli has an extensive paternal behavior repertoire whereas the closely-related Phodopus sungorus is not paternally responsive to a displaced pup. For the first time in a naturally paternal mammal, male estradiol and progesterone were determined during two critical phases: (1) the transition from sexually naive male to paired, expectant father that occurs in the absence of stimuli from pups (sexually naive males, paired males on G8, G12, G15, or G17 of the 18-day gestation) and (2) after pup stimuli became available to the males (paired males on days L1, L3, L5, or L12 of pup development). Hormone concentrations in naive males and between G17 and L1 (as stimuli from the birth and the pups became available to males) were also compared. Paternal responsiveness was tested on L3-L5 and confirmed species differences. Hormone concentrations in naive males were similar in the two species and males of both species had estradiol concentrations as high as fertile adult females. However, in direct contrast to predictions, estradiol concentrations were stable in P. campbelli males but increased before the birth, fell across the birth, and increased over pup development in P. sungorus males. Progesterone concentrations in P. campbelli males increased from G17 to L1 whereas a decrease had been predicted. Testosterone dynamics were consistent with previous studies. Either hormonal facilitation of paternal behavior is a hyper-variable trait that has evolved differently in different species, or, more probably, peripheral hormone concentrations are inadequate to explain the role of sex steroid hormones in paternal behavior.     

Divergent reproductive endocrinology of the estrous cycle and pregnancy in dwarf hamsters (phodopus)

Progesterone (P4) and prolactin (PRL) in peripheral circulation of Siberian hamsters (Phodopus sungorus) throughout an estrous cycle and pregnancy were determined by repeated, small volume sampling from individuals housed in modified home cages. As predicted, the endocrinology of P. sungorus reproduction is similar to the rat, mouse and golden hamster and shows none of the eight distinctive features known for Djungarian hamsters (Phodopus campbelli). Specifically, in P. sungorus there is no evidence for resumption of pituitary PRL surges in late pregnancy, P4 concentrations during the differentiation of the corpus luteum on day 2 of pregnancy are higher (as opposed to lower) than concentrations on the comparable day of an unmated estrous cycle (diestrus 1), P4 concentrations increase throughout pregnancy, PRL surges are common during the estrous cycle, including a reliable surge on proestrus, and P4 plays an important role in facilitating the expression of behavioral receptivity. We conclude that 'novel' P. campbelli reproductive endocrinology has evolved since a common ancestor was shared with P. sungorus. With a time frame (the available time since the divergence of the two species) and an ecological context (known niches and behavior in the wild) these species offer the opportunity to study endocrinological evolution in progress.     

Nomenclature of the metaphase chromosomes of the djungarian hamster

The proposed nomenclature of G-banded chromosomes of Phodopus sungorus campbelli is based on requisites and principles of the International System for Human Cytogenetic Nomenclature (ISCN).     

The functional capacities of the kidneys in hamsters of the genus Phodopus

Studies have been made on total osmolarity and concentration of Na and K in the urine, as well as on the level of diuresis in three species of the hamsters (Phodopus sungorus, Ph. campbelli, Ph. roborovskii) under the conditions of presence or absence of wet food and during water and salt loading. Mean value of osmotic concentration of the urine at free access to wet food varied within 2,600-3,500 mosmol, under the condition of dry-eating--within, 5,600--6,400 mosmol, which indicates the existence of a highly effective renal mechanism of water economy in the investigated species. At the same time, the capacity to maintain constant body weight in animals fed only air-dried food was noted only in separate specimens. In experiments with water load (30 microliters/g), the volume of fluid excreted within 4 hours amounted up to 87% of the load for Ph. sungorus, 70%--for Ph. campbelli and 43% for Ph. roborovskii. Studies on sodium and potassium contents of the urine under the conditions of dry-eating and salt loading indicate that the species investigated are capable of cation concentrating, yet they do not reveal any special mechanisms accounting for the excretion of excessive salts.     

黑线毛足鼠和金仓鼠血清IgG的纯化及抗血清的制备

目的 纯化黑线毛足鼠和金仓鼠血清IgG,制备兔抗金仓鼠和黑线毛足鼠血清IgG的抗血清。方法 用Hitrap Protein G亲和层析纯化黑线毛足鼠和金仓鼠血清IgG,经SDS-PAGE电泳鉴定纯度,标准免疫方法免疫兔子制备抗血清。结果 黑线毛足鼠和金仓鼠血清IgG对protein G有很高的亲合性,用Hitrap Protein G亲和层析纯化,得到高纯度黑线毛足鼠和金仓鼠IgG,利用纯化的IgG作抗原制备了高效价的抗血清,免疫双扩散测定效价达1∶32和1∶16。结论 证实黑线毛足鼠和金仓鼠IgG和Protein G具有很高的亲和性,Protein G亲和层析是纯化黑线毛足鼠和金仓鼠IgG有效的方法之一,制备了黑线毛足鼠和金仓鼠IgG的抗血清。     

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.     

Dopamine agonist treatment before and after the birth reduces prolactin concentration but does not impair paternal responsiveness in Djungarian hamsters, Phodopus campbelli

Male Djungarian hamsters, Phodopus campbelli, are highly parental and experience a late-afternoon prolactin surge before the birth that is not seen in a closely related species, P. sungorus, which lacks paternal care. At the same stage, female prolactin is needed for later maternal behavior. Male prolactin was suppressed in first-time fathers before the birth of the litter using two different dopamine agonists, bromocriptine mesylate and cabergoline. Plasma prolactin concentration confirmed the efficacy of each treatment. Paternal responsiveness was quantified using three variations on a pup-displacement paradigm. No adverse effects of either treatment were seen. Across four experiments, there was no decrease in paternal retrieval or in retrieval latency in response to male prolactin suppression. In addition, there was no decrease in litter growth or survival, nor was there an increase in maternal investment to compensate for a deficit in paternal care. As cabergoline suppression of prolactin persisted after the birth without behavioral deficits, prolactin after the birth was also not required for the expression of paternal behavior. In spite of an extensive literature supporting an association between prolactin and natural paternal behavior, we conclude that dopamine-mediated prolactin release into peripheral plasma is not essential for paternal responsiveness in P. campbelli.     

Chemosensory stimulation of luteinizing hormone secretion in male Siberian hamsters (Phodopus sungorus)

Male Siberian hamsters (Phodopus sungorus) housed in long days (LD), but not short days (SD) release luteinizing hormone (LH) when exposed to females. This study examined whether this response is specific to a female and identifies the source of a stimulus that induces LH release. Serum concentrations of LH, testosterone (T), follicle stimulating hormone (FSH), and cortisol were examined in all experiments. T concentrations mirrored the LH response; FSH and cortisol were unchanged in response to all stimuli. Exposure to an LD female, irrespective of her reproductive status, but not an SD female, elicited LH release. Exposure to another male did not trigger LH release. Males released LH when allowed physical contact with an anesthetized female, but not when separated from a normally active female, suggesting that tactile or nonvolatile chemosensory stimuli elicit LH release. Urine and secretions collected from the vagina as well as oral, midventral, perineal, and rectal glands, elicited marked behavioral responses in male P. sungorus. Despite these behavioral responses, only feces from females elicited LH release in males. Males released LH in response to feces extracted from the rectum and to cotton swabs that had been rubbed against the rectal mucosa, suggesting that a component of rectal secretions may trigger LH release in male Siberian hamsters. Taken together, these data and previous data from our laboratory indicate that both the production of and the response to a pheromone that triggers the selective release of LH is regulated by day length.     

Lipolytic and antilipolytic responses of the Siberian hamster (Phodopus sungorus sungorus) white adipocytes after weight loss induced by short photoperiod exposure

Short day photoperiod promotes thermogenesis and extensive weight loss in Siberian hamsters (Phodopus sungorus sungorus). To determine whether a change in hormone-sensitive lipolysis occurs after short-photoperiod exposure, some lipolytic responses were measured on white adipocytes isolated from animals exposed in warm conditions to short or Long daylight photoperiod. The body mass of male Siberian hamsters exposed during 11 weeks to short days (SD; light: dark, 6:18 hr) reached only 50% of those kept in long days (LD; 16: 8 hr). In SD-hamsters, adipose depot mass also represented approximately 50% of the LD group. A lower DNA content was observed in intra-abdominal fat pads of SD-hamsters. Lipolytic responses to noradrenaline, adrenaline, isoproterenol and ACTH were unchanged. However, sensitivity to the beta-3 adrenergic agonist, BRL 37344, was moderately increased. The major component of the adrenergic control of lipolysis was mediated by beta-3 adrenoceptors in both LD- and SD-Siberian hamsters. The limited antilipolytic effect of alpha-2 adrenergic agonists, PYY or insulin was rather surprising in Siberian hamsters since these inhibitory systems are efficient in hibernants and other photoperiod-sensitive rodents. Our results show that, after short photoperiod exposure, white adipose tissue mass and DNA content are reduced, especially in the epididymal fat pad, with only minor changes in the adipocyte sensitivity to lipolytic hormones.     

Effects of 60 Hz magnetic field exposure on the pineal and hypothalamic-pituitary-gonadal axis in the Siberian hamster (Phodopus sungorus)

Experiments using the dwarf Siberian hamster Phodopus sungorus were carried out to determine possible neuroendocrine consequences of one-time and repeated exposures to 60 Hz magnetic fields (MF). Animals were maintained in either a short-light (SL, 8 h light:16 h dark) or long-light (LL, 16 h light:8 h dark) photoperiod. Acute (one-time, 15 min) exposure of male SL animals to a linearly polarized, horizontally oriented, 60 Hz MF (0.1 mT) gave rise to a statistically significant (P < .005) reduction in pineal melatonin content as determined 3 and 5 h after onset of darkness. In LL animals, acute exposure to 0.10 mT resulted in a significant decrease in pineal melatonin as measured 4 h after onset of darkness, whereas acute exposure to 50 microT showed no effect compared with sham exposure. In SL animals, an increase in norepinephrine was observed in the medial basal hypothalamus (including the suprachiasmatic nucleus) after acute exposure (P < .01). Daily MF exposure of SL animals to a combination of steady-state and on/off 60 Hz magnetic fields (intermittent exposure) at 0.1 mT for 1 h per day for 16 days was associated with a reduction in melatonin concentrations at 4 h after onset of darkness and an increase in blood prolactin concentrations (P < .05). Exposure of SL animals to a steady state 60 Hz MF for 3 h/day for 42 days resulted in a statistically significant reduction in body weight (ANOVA: P > .05), compared with sham-exposed SL animals. At 42 days, however, no significant changes in overnight melatonin or prolactin levels were detected. In both repeated exposure experiments, gonadal weights were lowest in the MF-exposed groups. This difference was statistically significant (P < .05) after 42 days of exposure. These data indicate that both one-time and repeated exposure to a 0.1 mT, 60 Hz MF can give rise to neuroendocrine responses in Phodopus.     

Regulation of the pineal melatonin concentration in the rat (Rattus norvegicus) and in the Djungarian hamster (Phodopus sungorus)

1. Rapid changes of melatonin concentration in pineals of rats (Rattus norvegicus) after isoproterenol administration or in the course of a day were accompanied by parallel changes of N-acetyltransferase but not of hydroxyindole-O-methyltransferase activity. 2. In pineals of Djungarian hamsters (Phodopus sungorus) the evening and morning melatonin changes were also parallel with N-acetyltransferase changes. 3. In both species, melatonin concentration during its rise had approached the maximum earlier than N-acetyltransferase reached its highest activity. 4. It is proposed that the N-acetyltransferase rhythm drives the melatonin rhythm both in rats and in Djungarian hamsters; the maximum melatonin production may, however, depend also on hydroxyindole-O-methyltransferase activity and substrate concentration.     

Dietary lipid saturation influences environmental temperature preference but not resting metabolic rate in the Djungarian Hamster (Phodopus sungorus)

Heterothermic rodents increase self-selection of diets rich in polyunsaturated fatty acids (PUFAs) when exposed to cold, short days, or short-day melatonin profiles, and Djungarian hamsters (Phodopus sungorus) do so in long days in response to cold exposure alone. To determine whether Djungarian hamsters are also capable of selecting a thermal environment in response to dietary lipid composition, continuously normothermic hamsters were fed either a PUFA-rich diet or a diet rich in saturated fatty acids (SFAs) for 6-10 wk and given a choice of thermal environments. As predicted, SFA-fed hamsters were more likely than PUFA-fed hamsters to occupy the single heated corner of their cage ([Formula: see text]) and were most likely to show this diet-related difference in behavior when T(a) fell within the thermal neutral zone. Respirometry revealed no effect of diet on whole-animal or mass-specific resting metabolic rate or on lower critical temperature. The results are more consistent with the homeoviscous adaptation hypothesis, which predicts that organisms should make physiological and/or behavioral adjustments that preserve membrane fluidity within a relatively small range, than with the membrane pacemaker hypothesis, which predicts that high PUFA content in membrane phospholipids should increase basal metabolic rate.     

Studies on sex chromosomes of four hamster species: Cricetus cricetus, Cricetulus griseus, Mesocricetus auratus, and Phodopus sungorus.

In this paper, we present an analysis of the sex chromosomes of four hamster species after application of different staining techniques. The mitotic X chromosomes show a striking similarity in G-banding pattern but rather great differences in their C-banding patterns. A presumably homologous euchromatic segment that exhibits two distinct G-bands appears in the X chromosome of each species. The Y chromosome of Cricetus cricetus is in contrast to those of the other species, because it reveals a relatively well-differentiated G- and C-banding pattern. In meiotic metaphase I, interstitial chiasmata can be found in the sex bivalents of Cricetus cricetus and Cricetulus griseus, whereas the gonosomes of Mesocricetus auratus and Phodopus sungorus sungorus are terminally associated. The regions that are involved in pairing or association are always heterochromatic.     

Effects of wheel running on photoperiodic responses of Djungarian hamsters (Phodopus sungorus)

Djungarian hamsters (Phodopus sungorus) were exposed to artificial short days either with access to a running wheel (RW) or without. Within 6 weeks RW hamsters considerably increased their body mass, whereas controls showed the typical body mass reduction. Estimation of paired testis weights indicated a decelerated testis regression in RW hamsters. Subsequent locking of RWs for 9 weeks led to a decline in body mass of RW animals in parallel to controls. Daily torpor was almost completely missing in hamsters with initially unlocked wheels. During the final phase when RWs were again unlocked (3 weeks), body mass of exercising hamsters increased again, while controls reached the nadir in body mass. In comparison to equiponderate long-day (LD) controls the relative liver weight of RW hamsters was significantly increased unlike the relative heart weight. However, the latter tended to be higher than in sedentary LD hamsters. A growth-stimulating effect of wheel running was proven by elongated femora in exercising short-day (SD) hamsters compared to SD controls and suggested by exercise-induced elevation of body mass in a further experiment under continuous LD conditions, indicating a growth-promoting effect of wheel running independent from the photoperiod.     

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.     

Early embryo development in the Siberian hamster (Phodopus sungorus)

Development of preimplantation embryos of the Siberian hamster (Phodopus sungorus) in vivo and in vitro was examined. The timing of early development in vivo was found to be slower than that reported for the golden hamster. Progression through the cleavage stages, cavitation, and hatching from the zona pellucida occurred later, with blastocyst formation beginning on the afternoon of day 4 and uterine attachment occurring early on day 5. In vitro, morulae, and early blastocysts collected on day 4 and cultured in serum-containing medium formed expanded blastocysts and some began to hatch from the zona pellucida. With extended culture, blastocysts attached and formed trophoblast outgrowths. Outgrowth was characterized by an initial migration of small cells from the blastocyst, followed by formation of a sheet of trophoblast giant cells. Differences in the morphology of outgrowth between the hamster and mouse suggest that further comparative studies with the Siberian hamster may be useful.