The pathology of the Mongolian Gerbil (Meriones unguiculatus): a review.

Both naturally occurring disease processes and experimental models of human disease in the Mongolian gerbil were reviewed. The gerbil was highly susceptible to cerebral infarction following unilateral ligation of one common carotid artery and was useful in studies of the pathogenesis of stroke. Spontaneous epileptiform seizures mimicked those of human idiopathic epilepsy, and both seizure-sensitive and resistant strains have been bred. Perhaps because of its more efficient nephron, the gerbil accumulated four to six times as much renal lead as the rat, and the gerbil has been proposed as an experimental model of lead nephropathy. On standard diets, about 10% of the animals became obese, and some showed decreased glucose tolerance, elevated serum immunoreactive insulin and diabetic changes in the pancreas and other organs. Some breeders exhibited hyperactivity of the adrenal cortex associated with hyperglycemia, hyperlipidemia and degenerative vascular disease. Although dietary supplements of cholesterol were toxic and did not induce atherosclerosis, the gerbil was useful in other studies of cholesterol absorption and metabolism. Spontaneous, insidious periodontal disease became evident after about 6 months on standard diets, and dental caries were induced by cariogenic diets or by pathodontic streptococci. Spontaneous neoplasia occurred in 8.4--24% of gerbils, usually after 2 years of life. Adrenal cortical, ovarian and cutaneous tumors were the most consistently reported neoplasms.     

Melanocytes in the Stria Vascularis and Vestibular Labyrinth of the Mongolian Gerbil (Meriones unguiculatus)

Inner ear melanocytes are mainly present in the cochlea, vestibular organ, and endolymphatic sac, but their exact biological function has not been determined. In this investigation, we study the pigment cells in the membranous labyrinth of the gerbil. The inner ear melanocytes of M. unguiculatus show an irregular dendritic shape with cytoplasmic processes. These cells are disposed following the distribution of striai marginal and vestibular dark cells that have an important metabolic activity. Gerbil inner ear melanocytes are characterized by the presence of melanosomes, which are homogeneously dense organelles, of variable size and shape, that are surrounded by a membrane. In these cells, the Golgi apparatus plays a important role in melanin synthesis. When melanocytes were incubated in L-DOPA solution, the vesicles and cisterns of the Golgi apparatus exhibited a positive tyrosinase reaction. An interesting observation is the relation between melanocytes and inner ear capillaries. Sometimes, near to sensory vestibular areas, the melanocytes were in contact with Schwann cells and with myelinated fibres of vestibular nerve. The ultrastructural findings of this investigation are consistent with the hypothesis that melanocytes may have functional significance in the inner ear.     

长爪沙鼠肥满度的年龄和季节特征

采用胴体重(去除内脏的体重,记为WN)替代传统计算公式中的体重(W)建立肥满度指标K′＝100WN／L^3(g／cm^3)对长爪沙鼠肥满度的年龄和季节变化特征进行研究。结果显示：该鼠肥满度年龄组间差异显,末成年个体的肥满度明显高于成年个体;各性别年龄组肥满度季节变化明显,趋势基本一致,春季高、夏季最低、秋季又行育肥。在春夏季繁殖期(8月以前),雌鼠的肥满度大于雄鼠。成年雌鼠秋季育肥时间晚于其他个体组。长爪沙鼠肥满度的年龄差异和季节变化反映了该鼠在不同生活时期对环境的生理适应特征和对策。此外,各月肥满度与当月及其后第4个月的夹捕率存在一定的相关关系,提示该指标在短期预测长爪沙鼠种群数量方面可能有其参考价值。     

Long Term Effects of Social Deprivation during Early Adulthood in the Mongolian Gerbil (Meriones unguiculatus)

The influence of isolation on ♂-♀♀ relationships was investigated. Animals isolated between 90 and 200 days of age showed more agonistic behaviour in paired encounters than controls. This difference disappeared when the animals had been housed with a cagemate. A secondary isolation late in life resulted in a more rapid onset of agonistic behaviour in the early isolates than in the controls. Thus it is concluded that the early isolation had a lasting influence, which only became evident after renewed isolation treatment.     

Chromatin Organization and Remodeling of Interstitial Telomeric Sites During Meiosis in the Mongolian Gerbil (Meriones unguiculatus)

Telomeric DNA repeats are key features of chromosomes that allow the maintenance of integrity and stability in the telomeres. However, interstitial telomere sites (ITSs) can also be found along the chromosomes, especially near the centromere, where they may appear following chromosomal rearrangements like Robertsonian translocations. There is no defined role for ITSs, but they are linked to DNA damage-prone sites. We were interested in studying the structural organization of ITSs during meiosis, a kind of cell division in which programmed DNA damage events and noticeable chromatin reorganizations occur. Here we describe the presence of highly amplified ITSs in the pericentromeric region of Mongolian gerbil (Meriones unguiculatus) chromosomes. During meiosis, ITSs show a different chromatin conformation than DNA repeats at telomeres, appearing more extended and accumulating heterochromatin markers. Interestingly, ITSs also recruit the telomeric proteins RAP1 and TRF1, but in a stage-dependent manner, appearing mainly at late prophase I stages. We did not find a specific accumulation of DNA repair factors to the ITSs, such as γH2AX or RAD51 at these stages, but we could detect the presence of MLH1, a marker for reciprocal recombination. However, contrary to previous reports, we did not find a specific accumulation of crossovers at ITSs. Intriguingly, some centromeric regions of metacentric chromosomes may bind the nuclear envelope through the association to SUN1 protein, a feature usually performed by telomeres. Therefore, ITSs present a particular and dynamic chromatin configuration in meiosis, which could be involved in maintaining their genetic stability, but they additionally retain some features of distal telomeres, provided by their capability to associate to telomere-binding proteins.     

Naturally-occurring neoplasms in the Mongolian gerbil, Meriones unguiculatus.

10 spontaneous tumours were observed. Several had not been previously reported for this species and 1 occurred in the youngest gerbil yet reported to have a spontaneous tumour. 7 of the 10 tumours originated from the female reproductive tract.     

Sister chromatid exchange in the Mongolian gerbil, Meriones unguiculatus

Sister chromatid exchange (SCE) studies have been performed in a variety of animals, both in vitro and in vivo, as well as in plants. To date, no such studies have been performed in any member of the gerbil sub-family (Gerbillinae). A new sister chromatid differential staining method was used with mice in vivo and has now been applied to the Mongolian gerbil, Meriones unguiculatus. With some modifications, this in vivo method was found to be highly reproducible in gerbils, and had consistently produced many metaphase cells with clear sister chromatid differentiation. The method involves subcutaneous implantation of a 50 mg slow-release BrdU pellet, the fluorochrome Hoechst 33258, phosphate buffering at pH 6.8, and incandescent light exposure.     

Lysosomal enzymes in oocytes of the Mongolian gerbil,Meriones unguiculatus

Summary Histochemical investigations reveal that the intact oocytes of the Mongolian gerbil, Meriones unguiculatus, contain numerous acid phosphatase positive granules in every follicular stage. Non-specific esterase is active in early oocytes only in a faint peripheral margin of the ooplasm and in the zona pellucida of large secondary and tertiary follicles.This investigation was supported by the Deutsche Forschungsgemeinschaft (Ko 742/1)     

Exteroceptive factors and pregnancy block in the Mongolian gerbil, Meriones unguiculatus

A series of experiments based on 150 newly mated, uni- and multi-parous Mongolian gerbils provided no evidence for the existence of pregnancy blocking due to a strangle male effect. The reduced level of fertility observed was attributed to stressful factors at critical times in the pregnancy. Treatment with 10 i.u. PMSG on the day following mating interrupted pregnancy and the majority of females mated again within 4 days.     

Postnatal development of the testis in the Mongolian gerbil, Meriones unguiculatus

The testicular development in gerbils was studied over 16-week periods starting from birth. Testicular weight and seminiferous tubule diameter increased considerably between 1 and 11 weeks of age. At 16 weeks the testicular weight was about 540 mg. Spermatogenesis commenced at about 2 weeks when mitoses first appeared in spermatogonia. Spermatozoa appeared in a few of the seminiferous tubules by 7 weeks and consistently so in all of the tubules at 10 weeks. Epididymal spermatozoa appeared first in the cauda epididymis at 10 weeks and were consistently present at 12 weeks. Formation of mature Leydig cells with a grouped perivascular arrangement appeared by 3 weeks and continuously so thereafter. From these results, it is evident that the male Mongolian gerbil is almost sexually matured by 10 to 12 weeks of age.     

Discrimination of individuals by odor in male Mongolian gerbils, Meriones unguiculatus

The ability to discriminate among individuals plays a fundamental role in the establishment of social relationships in animals. We examined how Mongolian gerbils (Meriones unguiculatus) discriminate among individuals using odor. In the first experiment, the ability of male gerbils to discriminate among five odor sources from different individuals was investigated using a habituation-dishabituation paradigm. After male gerbils had been habituated to a scent from one individual, they were exposed to familiar and unfamiliar scents from different donors simultaneously. Where urine and ventral gland secretions were used, the subjects spent more time investigating novel odors than familiar ones, suggesting that they were able to discriminate individual differences in these odor sources. However, with the scents of feces and saliva, they could detect, but could not discriminate individual differences; with scent from inside the pinnae, they could not even detect. In the second experiment, we tested whether cross-habituation occurred between the scents of urine and ventral gland secretions. A male was exposed repeatedly to urine from one of two familiar donor males during four habituation trials, and was then exposed to the ventral gland secretions from two donors simultaneously. The subject males spent more time investigating scents of ventral gland secretions, but there was no difference in the investigation time between ventral gland scents from the two donors. These results suggest that male gerbils discriminate among individuals using odors from urine and ventral gland secretions and that cross-habituation may not occur between these scents during social-memory formation.