Warfarin-resistance genotype determination in the Norway rat, Rattus norvegicus

The 2-stage determination is based on changes in blood coaggulation activity brought about both by the administration of warfarin in conjunction with vitamin K1 epoxide and by feeding a vitamin K-free diet for 4 days. When it was applied to laboratory-bred rats of known warfarin-resistance genotype, 35/35 homozygous susceptible, 44/44 homozygous resistant and 131/133 heterozygous rats were correctly classified. This method was equally effective in identifying the genotype of wild rats carrying the warfarin-resistance gene, Rw2. The procedure is rapid and accurate.     

High resolution chromosome banding in the Norway rat, Rattus norvegicus

High resolution banded chromosomes were prepared from a synchronized culture of rat fibroblasts. A maximum of 457 bands per haploid chromosome set were observed. This represents a two-fold increase when compared to the number of bands visualized in mid-metaphases using standard procedures. By reference to both G- and Q-banded karyotypes, we constructed improved idiograms of rat chromosomes at 300- and 400-band stages, respectively.     

Chromosome markers in 12 inbred strains of the Norway rat, Rattus norvegicus.

Morphological details of metaphase chromosomes were compared among 12 inbred strains of rats (Rattus norvegicus) by means of conventional Giemsa staining and by a sequential Q- and C-banding method. Inter-strain variations were found in seven pairs, as identified on the basis of size differences in the short arms and/or satellites of chromosomes 3 and 12 and the X chromosome and in the centromeric C-bands of chromosomes 4, 5, 7, and 9. All pairs were homomorphic in the inbred strains, while F1 hybrids between two inbred strains showed certain heteromorphic pairs expected from the parents. These chromosome markers appear to be useful for characterization of inbred strains as well as for various genetic studies, including linkage analyses.     

The morphological sequence of XY pairing in the Norway rat Rattus norvegicus

The sequence of XY pairing at meiotic prophase in the Norway rat, Rattus norvegicus, has been studied in spread preparations of spermatocytes obtained from pubertal males. As in most mammals, sex chromosome pairing is delayed in relation to that of the autosomes. At one stage in pachytene, the Y is fully paired in synaptonemal complex association with about one-third of the X. Observation in spread preparations at pachytene and diplotene and in air-dried metaphase I preparations indicates that the long arm of the Y pairs with the short arm of the X. Pairing of the Y with both ends of the X is seen in about 4% of pachytene spermatocytes. The possibility that XY pairing in the rat may be nonhomologous (Ashley 1983) is considered, and the view is expressed that the XY synaptonemal complex may be incomplete in fine structural detail, thus not providing for the effective pairing required in true reciprocal recombination. The same mechanism that excludes crossing over from heterochromatic regions of autosomes may also operate to minimize or prevent crossing over in the sex pair of mammals.     

Autosomal and sex-chromosomal polymorphism in a wild population of the Norway rat,Rattus norvegicus

The karyotypes of 33 specimens of Rattus norvegicus captured in a wild population, were studied by means of conventional Giemsa staining and G- and C-banding methods. A chromosomal polymorphism for the presence or absence of extra segments in autosomes 3 and 12 and the X chromosome was found, beside a polymorphism for centromeric C-bands in pair no. 6.The frequency of different chromosome types found in this population was compared with that found in a wild population in Japan as well as with that found in some inbred strains.     

Linkage analyses among five esterase loci in the laboratory rat (Rattus norvegicus)

A cluster of esterase loci has been identified on a segment of a rat linkage group V; however, the linear order of all the loci has not been established. We estimated the recombination frequencies of two locus combinations among five esterase loci (Es-1, Es-2, Es-3, Es-4, and Es-Si) and the linear order of the loci by using three sets of backcross matings: (1) (K:W × IS) × IS, (2) (K:W × IS) × IS, and (3) (SHR × W) × W). The linear order was determined to be Es-1-Es-4-Es-2-Es-3-Es-Si, although the order of Es-2 and Es-4 remains tentative. The sexinfluenced esterase (Es-Si) was demonstrated to be distinct from Es-1 and was proposed to be Es-Si locus with two alleles of Es-Si ^a (positive) and Es-Si ^b (null).This work was partly supported by Grants-in-Aid for Scientific Research, No. 339020 (1978), from the Ministry of Education, Science and Culture, Japan.     

Blood sampling from the cranial vena cava in the Norway rat (Rattus norvegicus)

This paper describes blood sampling from the cranial vena cava (CVC) in the Norway rat. In order to limit stress, the blood sampling should be done under short-term inhalation anaesthesia, for example, an oxygen/isoflurane mixture. The injection site is just cranial to the first rib, 0.3-0.8 cm lateral to the manubrium when the animal is in dorsal recumbency. The needle, attached to a syringe, is inserted at 30 degrees in the direction of the opposite femoral head. After penetration of the skin, negative pressure is developed in the syringe and the insertion of the needle is continued for another 0.2-1 cm in the given direction until blood begins to flow. The amount of blood sampled ranges from 0.8 to 2.5 mL depending on the body weight of the patient. A trial on 50 rats aged 5-24 months included 25 rats sampled once, eight rats sampled twice with an interval of seven days, 11 rats sampled twice with an interval of three weeks and four rats sampled four times with intervals of four weeks--a total of 87 blood samplings. The serious complications quoted in association with blood sampling from the CVC in other experimental animals (vascular lacerations, heart puncture, serious haemorrhage, tracheal and throat trauma) were not observed in our study. There were only four blood samplings (4.5%) with mild haemorrhage from the injection site, due to erroneous sampling from the jugular vein.     

Completion of the life cycle of Sarcocystis zuoi , a parasite from the Norway rat, Rattus norvegicus

Transmission experiments were performed to elucidate the life cycle of Sarcocystis zuoi found in Norway rats ( Rattus norvegicus ) in China. Two king rat snakes ( Elaphe carinata ) fed sarcocysts from the muscles of 4 naturally infected Norway rats shed sporocysts measuring 10.8 ± 0.7 × 8.0 ± 0.7 μm, with a prepatent period of 8-9 days. Sporocysts from the intestine of 2 experimentally infected king rat snakes were given to the laboratory Sprague-Dawley (SD) rats ( R. norvegicus ) and Kunming (KM) mice ( Mus musculus ). Microscopic sarcocysts developed in the skeletal muscles of SD rats. No sarcocysts were observed in KM mice. Characters of ultrastructure and molecule of sarcocysts from SD rats were confirmed as S. zuoi . Our results indicate that king rat snake is the definitive host of S. zuoi .     

Natural Echinococcus multilocularis infection in a Norway rat, Rattus norvegicus, in southern Hokkaido, Japan.

Forty-two rats, Rattus norvegicus, captured at a garbage dump in southern Hokkaido, Japan, were examined, and one was found to be infected with Echinococcus multilocularis. The lesions were found in the liver, lung, mesenteric lymph nodes, greater omentum and also free in the abdominal cavity. No necrosis was observed in any of the lesions, and inflammatory reactions were mild. Protoscoleces were observed in the large liver cysts. A homogenate of these cysts, when transplanted into the abdominal cavity of three Mongolian gerbils and a rat, yielded numerous fully developed protoscoleces at 4-7 months post-inoculation. Judging from this, it is postulated that the rat could become a natural intermediate host for E. multilocularis in this area.     

Linkage of a plasma protein marker (Gl-1) and the Hooded locus in the rat,Rattus norvegicus

The linkage of the plasma protein (Gl-1) and hooded loci has been determined from backcross progeny of the initial crosses Long Evans/Orl×BN/Orl and Long Evans/Orl×Fatty/Orl. The two sets of data show a significant linkage heterogeneity with, respectively, 5.0±2.8 and 15.1±3.0 recombination. This is the fourth linkage of biochemical markers so far demonstrated in the rat.     

Characterization of silver-stained nucleolus organizer regions (Ag-NORs) in 16 inbred strains of the Norway rat, Rattus norvegicus

Silver-stained nucleolus organizer regions (Ag-NORs) in metaphase chromosomes of cultured fibroblasts were compared among 16 inbred strains of the Norway rat, Rattus norvegicus. Ag-NORs were located at the secondary constrictions or juxtacentromeric regions of the short arms of chromosomes 3, 11, and 12. The frequency and relative size of Ag-NORs were found to be strain-specific, providing a genetic marker system useful for characterization of inbred strains. While considerable cell-to-cell variation was observed within a given strain, the strain-specific pattern of Ag-NORs was shown to be consistent in cultured and noncultured cells obtained from different tissues of embryos, newborns, and adults, as well as in successively cultured cells examined up to the 10th subculture generation. The patterns of Ag-NORs in F1 hybrids made between some of the inbred strains were in general agreement with those expected from the parental strains; some unexpected patterns were noted in F1 hybrids of a particular cross, suggesting the possible existence of nucleolar interactions in such interstrain hybrids, although this has to be confirmed.     

Glucose phosphate dehydrogenase polymorphism and the genetics of linkage group II in the Norway rat (Rattus norvegicus)

A new variant of glucose phosphate dehydrogenase was discovered in rat erythrocytes and shows autosomal dominant inheritance. The locus, provisionally denoted Gpd, is closely linked to catalase (Cs-1), and there is some evidence that these loci may be assignable to linkage group II. Also in linkage group II, Pgd (6-phosphogluconate dehydrogenase) was found to be linked to b (brown). The linkage between Pgd and b permits linkage group II to be assigned to chromosome 5.     

Skull growth in the albino rat (Rattus norvegicus)

A longitudinal study of growth in the rat skull, based on serial radiographs, has shown that by the age of one month after birth, the braincase attains some 93% of its adult (fifth-month) size whilst the facial skeleton and mandible attain but 75% of their adult size. By the third month, growth in the braincase has virtually ceased, whereas significant facial growth continues until the age of five months.     

The gene map of the Norway rat (Rattus norvegicus) and comparative mapping with mouse and man

The current status of the rat gene map is presented. Mapping information is now available for a total of 214 loci and the number of mapped genes is increasing steadily. The corresponding number of loci quoted at HGM10 was 128. Genes have been assigned to 20 of the 22 chromosomes in the rat. Some aspects of comparative mapping with mouse and man are also discussed. It was found that there is a good correlation between the morphological homologies detectable in rat and mouse chromosomes, on the one hand, and homology at the gene level on the other. For 10 rat synteny groups all the genes so far mapped are syntenic also in the mouse. For the remaining rat synteny groups it appears that the majority of the genes will be syntenic on specific (homologous) mouse chromosomes, with only a few genes dispersed to other members of the mouse karyotype. Furthermore, the data indicate that mouse chromosome 1 genetically corresponds to two rat chromosomes, viz., 9 and 13, equalizing the difference in chromosome number between the two species. Further mappings will show whether the genetic homology will prove to be as extensive as these preliminary results indicate. As might be expected from evolutionary considerations, rat synteny groups are much more dispersed in the human genome. It is clear, however, that many groups of genes have remained syntenic during the period since man and rat shared a common ancestor. One further point was noted. In two cases groups of genes were syntenic in the mouse but dispersed to two chromosomes in rat and man, whereas in a third case a group of genes was syntenic in the rat but dispersed to two chromosomes in mouse and man. This finding argues in favor of the notion that the original gene groups were on separate ancestral chromosomes, which have fused in one rodent species but remained separate in the other and in man.