Dwarf Hamster Phodopus Sungorus Research Articles

Chromosome Synapsis and Recombination in Male-Sterile and Female-Fertile Interspecies Hybrids of the Dwarf Hamsters (Phodopus, Cricetidae).

Hybrid sterility is an important step in the speciation process. Hybrids between dwarf hamsters Phodopus sungorus and P. campbelli provide a good model for studies in cytological and genetic mechanisms of hybrid sterility. Previous studies in hybrids detected multiple abnormalities of spermatogenesis and a high frequency of dissociation between the X and Y chromosomes at the meiotic prophase. In this study, we found that the autosomes of the hybrid males and females underwent paring and recombination as normally as their parental forms did. The male hybrids showed a significantly higher frequency of asynapsis and recombination failure between the heterochromatic arms of the X and Y chromosomes than the males of the parental species. Female hybrids as well as the females of the parental species demonstrated a high incidence of centromere misalignment at the XX bivalent and partial asynapsis of the ends of its heterochromatic arms. In all three karyotypes, recombination was completely suppressed in the heterochromatic arm of the X chromosome, where the pseudoautosomal region is located. We propose that this recombination pattern speeds up divergence of the X- and Y-linked pseudoautosomal regions between the parental species and results in their incompatibility in the male hybrids.

Effect of Exercise on Photoperiod-Regulated Hypothalamic Gene Expression and Peripheral Hormones in the Seasonal Dwarf Hamster Phodopus sungorus

The Siberian hamster (Phodopus sungorus) is a seasonal mammal responding to the annual cycle in photoperiod with anticipatory physiological adaptations. This includes a reduction in food intake and body weight during the autumn in anticipation of seasonally reduced food availability. In the laboratory, short-day induction of body weight loss can be reversed or prevented by voluntary exercise undertaken when a running wheel is introduced into the home cage. The mechanism by which exercise prevents or reverses body weight reduction is unknown, but one hypothesis is a reversal of short-day photoperiod induced gene expression changes in the hypothalamus that underpin body weight regulation. Alternatively, we postulate an exercise-related anabolic effect involving the growth hormone axis. To test these hypotheses we established photoperiod-running wheel experiments of 8 to 16 weeks duration assessing body weight, food intake, organ mass, lean and fat mass by magnetic resonance, circulating hormones FGF21 and insulin and hypothalamic gene expression. In response to running wheel activity, short-day housed hamsters increased body weight. Compared to short-day housed sedentary hamsters the body weight increase was accompanied by higher food intake, maintenance of tissue mass of key organs such as the liver, maintenance of lean and fat mass and hormonal profiles indicative of long day housed hamsters but there was no overall reversal of hypothalamic gene expression regulated by photoperiod. Therefore the mechanism by which activity induces body weight gain is likely to act largely independently of photoperiod regulated gene expression in the hypothalamus.

Endocrine mechanisms of seasonal adaptation in small mammals: from early results to present understanding

Seasonal adaptation is widespread among mammals of temperate and polar latitudes. The changes in physiology, morphology and behaviour are controlled by the photoneuroendocrine system that, as a first step, translates day lengths into a hormonal signal (melatonin). Decoding of the humoral melatonin signal, i.e. responses on the cellular level to slight alterations in signal duration, represents the prerequisite for appropriate timing of winter acclimatization in photoperiodic animals. Corresponding to the diversity of affected traits, several hormone systems are involved in the regulation downstream of the neural integration of photoperiodic time measurement. Results from recent studies provide new insights into seasonal control of reproduction and energy balance. Most intriguingly, the availability of thyroid hormone within hypothalamic key regions, which is a crucial determinant of seasonal transitions, appears to be regulated by hormone secretion from the pars tuberalis of the pituitary gland. This proposed neuroendocrine pathway contradicts the common view of the pituitary as a gland that acts downstream of the hypothalamus. In the present overview of (neuro)endocrine mechanisms underlying seasonal acclimatization, we are focusing on the dwarf hamster Phodopus sungorus (long-day breeder) that is known for large amplitudes in seasonal changes. However, important findings in other mammalian species such as Syrian hamsters and sheep (short-day breeder) are considered as well.

Neurochemistry of Olivocochlear Neurons in the Hamster

The present study was conducted to characterize the superior olivary complex (SOC) of the lower brain stem in the pigmented Djungarian hamster Phodopus sungorus. Using Nissl-stained serial cryostat sections from fresh-frozen brains, we determined the borders of the SOC nuclei. We also identified olivocochlear (OC) neurons by retrograde neuronal tracing upon injection of Fluoro-Gold into the scala tympani. To evaluate the SOC as a putative source of neuronal nitric oxide synthase (nNOS), arginine-vasopressin (AVP), oxytocin (OT), vasoactive intestinal polypeptide (VIP), or pituitary adenylate cyclase-activating polypeptide (PACAP) that were all found in the cochlea, we conducted immunohistochemistry on sections exhibiting retrogradely labeled neurons. We did not observe AVP-, OT-, or VIP-immunoreactivity, neither in OC neurons nor in the SOC at all, revealing that cochlear AVP, OT, and VIP are of nonolivary origin. However, we found nNOS, the enzyme responsible for nitric oxide synthesis in neurons, and PACAP in neuronal perikarya of the SOC. Retrogradely labeled neurons of the lateral olivocochlear (LOC) system in the lateral superior olive did not contain PACAP and were only infrequently nNOS-immunoreactive. In contrast, some shell neurons and some of the medial OC (MOC) system exhibited immunofluorescence for either substance. Our data obtained from the dwarf hamster Phodopus sungorus confirm previous observations that a part of the LOC system is nitrergic. They further demonstrate that the medial olivocochlear system is partly nitrergic and use PACAP as neurotransmitter or modulator.

Photoperiodic Differences during Development in the Dwarf Hamsters Phodopus sungorus and Phodopus campbelli

The dwarf hamsters Phodopus sungorus and to a lesser extent Phodopus campbelli are widely used to study pineal physiology and seasonal reproduction because of their marked responses to photoperiod in adulthood. These species are frequently confused, partly because the common names "Siberian hamster" and "Djungarian hamster" are applied to both, often interchangeably. The current study examines whether the effects of photoperiod on reproductive maturation and prolactin secretion differ between these closely related species. Both male and female P. sungorus and P. campbelli were gestated and raised in long days (LD) of 16 hr light: 8 hr dark or in short days (SD) of 8 hr dark: 16 hr light. They were raised in pairs of the same sex after weaning at 21 days of age. Reproductive organ weights and serum prolactin concentrations were studied at 35 and 70 days of age. Whereas reproductive development proceeded rapidly in LD in both male and female P. sungorus, SD photoperiod completely inhibited growth of the gonads during this study. There were also marked differences in serum prolactin concentrations in both sexes of P. sungorus at all ages: levels were approximately 10-fold higher in LD than in SD. In P. sungorus of both sexes, SD also significantly decreased body weight relative to conspecifics raised in LD. In P. campbelli, reproductive maturation in LD occurred even more rapidly than in P. sungorus. Although significant effects of photoperiod were still apparent, the magnitude of its effect was less marked than in P. sungorus, and a substantial degree of reproductive development was observed in SD-reared males and females. There was no significant effect of photoperiod on serum prolactin concentrations at either age in P. campbelli, and the effects on body weight gain were inconsistent. Breeding rates were also compared between the two species. Litter size was significantly larger in P. campbelli and neonatal loss was less; consequently more pups survived to weaning. The interbirth interval was also shorter in P. campbelli than in P. sungorus (mode: 20 vs 24 days). The marked photoperiodic differences in reproductive development and prolactin secretion and the differences in breeding success between P. sungorus and P. campbelli clearly distinguish these species.

Comparative investigations of the cellular and subcellular distribution of brain creatine kinase and [formula omitted] activity of cichlid fish and dwarf hamster

Cellular (=total homogenate) and subcellular fractions (P1a-pellet, cytosolic fraction SN3, P4-pellet, P8-pellet, synaptosomal and synaptic membrane fraction) of brain tissue of the cichlid fish Oreochromis mossambicus and the Djungarian dwarf hamster Phodopus sungorus were collected and the distribution of creatine kinase (CK) and different Ca 2+−Mg 2+-ATPase activities in each fraction were studied. The data obtained from cellular as well as from subcellular fractions indicate less CK, Ca 2+- and ( Ca 2+−Mg 2+ )-ATPase activities in cichlid fish than in hamster brain. The dwarf hamster expressed higher enzyme activity in the brain as compared to the cichlid fish only in regard to the Mg 2+-ATPase activity and with the exception of synaptic membranes.

Development of Phodopus sungorus brown preadipocytes in primary cell culture: effect of an atypical beta-adrenergic agonist, insulin, and triiodothyronine on differentiation, mitochondrial development, and expression of the uncoupling protein UCP.

A new cellular model for the study of brown adipocyte development and differentiation in vitro is presented. Preadipocytes isolated from brown adipose tissue (BAT) of the djungarian dwarf hamster Phodopus sungorus are able to proliferate and differentiate in vitro into true brown adipocytes able to express the BAT marker protein the uncoupling protein (UCP). Whereas basal UCP expression is very low, its mRNA levels as well as the UCP detected by immunoblotting are highly increased by beta-adrenergic stimulation. The novel, atypical beta-adrenergic compound D7114 (ICI Pharmaceuticals, Macclesfield, Cheshire, England) was found to increase the number of adipocytes as well as UCP mRNA and UCP content of mitochondria, indicating the involvement of an atypical or beta 3 receptor. Insulin was found to play an important role in brown adipocyte differentiation and mitochondrial development, whereas T3 seemed to be implicated more directly in UCP expression. In a defined, serum-free medium a synergistic stimulatory action of insulin and T3 on UCP expression was found, which seems to involve a pathway different from that of beta-adrenergic UCP stimulation.

Long terminal repeats of dwarf hamster endogenous retrovirus are highly diverged and do not maintain efficient transcription

Recently we described a new endogenous proretrovirus of dwarf hamster Phodopus sungorus (MRS-Ps). Its sequence possesses evident homology with the endonuclease domain of the mouse mammary tumor virus pol gene. Here we present nucleotide sequence data on three clones of retroviral long terminal repeats. As many as 15% of substituted, deleted, and inserted base pairs were found while comparing these sequences. Hence, MRS-Ps seems to be rather an old genetic element which originated about 30 million years ago. One LTR is 877 by long and contains numerous elements that control its transcriptional activity: TATA-box, glucocorticoid responsive element, NF1-binding site, etc. Nevertheless, this LTR does not govern efficient transcription of adjacent genes in a transient expression assay. In addition, we failed to find MRS-specific mRNA in adult, embryonic, and mammary tumor cells.

Brain Ca 2+/Mg 2+ -ATPase activity and seasonal adaptation of the djungarian dwarf hamster Phodopus sungorus

1. 1. Of three sets of Djungarian dwarf hamster, two groups were raised during winter under greatly differing circumstances. One winter group was raised within a climate controlled cage in which the ambient temperature was maintained at 22°C and whereby conditions of light vs darkness were maintained in a constant 12hr cycle. The second winter group was raised out of doors whereby the hamsters were subjected to prevailing seasonal environmental conditions. A third group was studied under summer conditions, as well. Ca 2+-, Mg 2+- and (Ca 2+/Mg 2+)-ATPase activity was analysed in cellular ( = total homogenate) and subcellular fractions (P1, synaptosomal fraction, synaptic membranes) from cortex, cerebellum and basal brain. 2. 2. The data obtained indicate similar ATPase activity in the cortical homogenates of the winter indoor and summer hamsters. 3. 3. Winter outdoor animals experiencing normal torpidity, however, exhibited reduced ATPase activity by about 50%. 4. 4. Cortical subcellular fractions yielded different results: both the winter and the summer groups showed high ATPase activity in the synaptosomal and synaptic membrane fractions. 5. 5. In the total cerebellar homogenate, the hamsters raised under summer and winter conditions showed the greatest enzyme activity, although less activity was seen in the subcellular fractions. 6. 6. The ATPase activity in the basal brain was found to be nearly identical in all three hamster groups.

Effect of food Deprivation on thermogenic capacity in the Djungarian dwarf hamster Phodopus sungorus

1. 1.|A reduction of the body weight of Djungarian hamsters from 45 to 25 g by a strict diet increased their weight-specific non-shivering thermogenesis (NST), but total capacity for NST and cold limit were unaffected. During seasonal acclimatization a similar reduction in body weight occurred. However, there was a significant improvement in total capacity for NST and cold limit, indicating that seasonal thermogenic adaptation occurs independently of seasonal changes in body weight. 2. 2.|Acute starvation for 43 h affected neither weight-specific nor total thermogenic capacities, indicating stability of heat production towards reductions of energy supply.