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At least 37 records · Page 2Linked to original sources
PubMed2003

Circadian regulation of gonadotropin-releasing hormone neurons and the preovulatory surge in luteinizing hormone in the diurnal rodent, Arvicanthis niloticus, and in a nocturnal rodent, Rattus norvegicus.

Daily rhythms in the timing of the preovulatory surge and the display of reproductive behavior are reversed in diurnal and nocturnal rodents, but little is known about the neural mechanisms underlying these differences. We examined this issue by comparing a diurnal murid rodent, Arvicanthis niloticus (the grass rat), to a nocturnal one, Rattus norvegicus (the lab rat). In the first study, we established that sequential estradiol and progesterone treatment induces a proestrous-like rise in LH secretion and in the percentage of GnRH neurons that express Fos in grass rats, as is the case in lab rats. Next, we tested the hypothesis that differences in the timing of estrus-related events in diurnal and nocturnal species are caused by differences in rhythms in responsiveness to steroid hormones. We found rhythms in GnRH neuron activity, as indicated by Fos, that were 12 hours out of phase in grass rats and lab rats. These patterns persisted in both species when animals were housed in constant darkness for 5 days, suggesting that they are driven by an endogenous circadian mechanism. These results indicate that steroid-primed grass rats and lab rats are similar with respect to the temporal relationship among estrus-related events, but that the timing of these events relative to the light-dark cycle is dramatically different and that this difference is caused by endogenous circadian mechanisms.

Animals↗
PubMed1977

Two distinct endogenous type C viruses isolated from the asian rodent Mus cervicolor: conservation of virogene sequences in related rodent species.

The cocultivation of a lung cell line from the Southeast Asian mouse Mus cervicolor with cells from heterologous species has resulted in the isolation of two new distinct type C viruses. Both viruses are endogenous to M. cervicolor and are present in multiple copies in the cellular DNA of these mice. One of the viruses, designated M. cervicolor type CI, replicates readily in the SIRC rabbit cell line and is antigenically related to the infectious primate type C viruses isolated from a woolly monkey (simian sarcoma-associated virus) and gibbon apes (gibbon ape leukemia virus). This virus is also closely related by both immunological and nucleic acid hybridization criteria to a type C virus previously isolated from a second Asian murine species, Mus caroli. The isolation of the M. cervicolor type C I virus thus provides further evidence that the infectious primate type C viruses originated by trans-species infection of primates by an endogenous virus of mice. The second virus, designated M. cervicolor type C II, replicates well in various cell lines derived from the laboratory mouse Mus musculus. While antigenically related to type C viruses derived from M. musculus, the M. cervicolor type C II virus isolate can be readily distinguished from standard murine leukemia viruses. Both new type C viruses from M. cervicolor are unrelated to the previously described retrovirus (M432) isolated from the same Mus species. The DNA of M. cervicolor therefore contains multiple copies of at least three distinct classes of endogenous viral genes. An examination of the cellular DNA of other rodent species for nucleic acid sequences related to the genomes of both M. cervicolor type C I and II reveals that both viruses have been highly conserved evolutionarily, and that other species of rodents, such as laboratory mice and rats, contain endogenous virogenes related to those in the DNA of M. cervicolor.

Animals↗
PubMed1999

Fos expression within vasopressin-containing neurons in the suprachiasmatic nucleus of diurnal rodents compared to nocturnal rodents.

The underlying neural causes of the differences between nocturnal and diurnal animals with respect to their patterns of rhythmicity have not yet been identified. These differences could be due to differences in some subpopulation of neurons within the suprachiasmatic nucleus (SCN) or to differences in responsiveness to signals emanating from the SCN. The experiments described in this article were designed to address the former hypothesis by examining Fos expression within vasopressin (VP) neurons in the SCN of nocturnal and diurnal rodents. Earlier work has shown that within the SCN of the diurnal rodent Arvicanthis niloticus, approximately 30% of VP-immunoreactive (IR) neurons express Fos during the day, whereas Fos rarely is expressed in VP-IR neurons in the SCN of nocturnal rats. However, in earlier studies, rats were housed in constant darkness and pulsed with light, whereas Arvicanthis were housed in a light:dark (LD) cycle. To provide data from rats that would permit comparisons with A. niloticus, the first experiment examined VP/Fos double labeling in the SCN of rats housed in a 12:12 LD cycle and perfused 4 h into the light phase or 4 h into the dark phase. Fos was significantly elevated in the SCN of animals sacrificed during the light compared to the dark phase, but virtually no Fos at either time was found in VP-IR neurons, confirming that the SCN of rats and diurnal Arvicanthis are significantly different in this regard. The authors also evaluated the relationship between this aspect of SCN function and diurnality by examining Fos-IR and VP-IR in diurnal and nocturnal forms of Arvicanthis. In this species, most individuals exhibit diurnal wheel-running rhythms, but some exhibit a distinctly different and relatively nocturnal pattern. The authors have bred their laboratory colony for this trait and used animals with both patterns in this experiment. They examined Fos expression within VP-IR neurons in the SCN of both nocturnal and diurnal A. niloticus kept on a 12:12 LD cycle and perfused 4 h into the light phase or 4 h into the dark phase, and brains were processed for immunohistochemical identification of Fos and VP. Both the total number of Fos-IR cells and the proportion of VP-IR neurons containing Fos (20%) were higher during the day than during the night. Neither of these parameters differed between nocturnal and diurnal animals. The implications of these findings are discussed.

Animals↗
PubMed1978

Rodent zoonoses in North Queensland: the occurrence and distribution of zoonotic infections in North Queensland rodents.

A study of potentially zoonotic infections was carried out on 351 rodents trapped in north-eastern Queensland. Their ecosystems included towns, agricultural and livestock areas, wookland and rainforest. Nine serotypes of salmonellae were obtained from asymptomatic carries in predominantly settled locations. Two strains of Ps. pseudomallei occurred in rainforest near Innisfail and one on a cattle property adjacent to Townsville. Ps. aeruginosa caused bronchopneumonia in one animal from Townsville harbour. Ifection by leptospirae of six serogroups and seven serovars were identified by serological or cultural examinations. Enzootic foci occurred on the Mount Spec rainforest where celledoni and australis were being excreted by rats adjacent to the Paluma dam system. In addition to the scrub typhus locations at Rocky Creek, Atherton Tableland and Bullocky Creek, near Ingham, which were confirmed, a new focus of infection by R. tsutsugamushi was identified at El Arish near Tully. Water rat (H. chrysogaster) at Townsville harbour constituted a reservoir of toxoplasmosis. In addition to the known human pathogenic helminths H. nana and H. diminuta, localized foci of hookworms (Ancylostoma spp.) were found. Histological evidence of cytomegalic disease of the salivary glands or kidneys was a common finding.

Animals↗
PubMed1993

Expression of the SmN splicing protein is developmentally regulated in the rodent brain but not in the rodent heart.

The SmN protein is a tissue-specific splicing factor which is closely related to the ubiquitous SmB splicing protein but which is expressed only in the adult brain and heart. SmN is also detectable albeit at a low level in both the embryonic brain and heart. During heart development, SmN levels remain constant while during rodent brain development the levels of SmN rise such that SmN replaces SmB as the predominant protein in adult brain. This increase in SmN levels is dependent upon a corresponding increase in the SmN mRNA which is detectable by in situ hybridization within neurons in virtually all areas of the adult brain.

Animals↗
PubMed1995

The fate of human glial cells following transplantation in normal rodents and rodent models of neurodegenerative disease.

Investigations on xenografting in the brain have previously focused on the anatomical and functional integration of the transplanted neurons. More recently, astrocytes are being implicated as having complex functions following transplantation, and are being investigated to determine their role(s) in transplantation. The present study was undertaken to investigate the migration of human astrocytes following transplantation of thalamic, striatal, and mesencephalic tissue into the rodent striatum. Human donor fetuses (9-16 weeks in gestation) obtained through elective and spontaneous abortions were utilized in this study. Following transplantation, donor astrocytes were labeled with an antiserum directed against human glial fibrillary acidic protein. Our results demonstrate that astrocytic elements from all three tissue types are capable of incorporating into the host brain, and have a tendency to follow white matter tracts (such as the corpus callosum, internal capsule, and fiber bundles in the striatum). Human astrocytes, originating from the striatum and thalamus exhibited extensive migration, while migration was more limited in animals with ventral mesencephalon transplants. Ventral mesencephalon transplanted animal demonstrated positive astrocytes within the transplant, with processes (very few cell bodies) extending into white matter of adjacent host striatum. Astrocytes demonstrating immature morphology were observed with all transplant types, but were most prevalent in the striatal transplanted animals. The extent of astrocyte migration and the morphologies observed in this study reflect regional differences of the developing human brain. These results confirm and extend previous investigations on glial cell migration following transplantation in the brain.

Animals↗
PubMed2006

Characterisation of the binding of amyloid imaging tracers to rodent Abeta fibrils and rodent-human Abeta co-polymers.

Despite the application of amyloid imaging agents such as PIB, SB13, and FDDNP in Alzheimer's disease (AD) patients, the successful use of these agents in transgenic mice models of AD has not been reported to date. As a first step in understanding the behaviour of these ligands in transgenic models of AD, we have investigated in a series of in vitro ligand binding assays the interaction of selected agents, including PIB, FDDNP, SB13, and BSB, with amyloid fibrils produced from rodent Abeta(1-40) (roAbeta) peptide. The data indicate that the ligand binding affinities together with the pattern and number of binding sites on the roAbeta fibrils are broadly conserved with that reported previously for human Abeta(1-40) (huAbeta) fibrils. However, characterisation of huAbeta fibrils formed in the presence of increasing amounts of roAbeta (1, 5, 10% w/w) demonstrated a dose-dependent reduction in the number of high affinity [(3)H]Me-BTA-1 binding sites such that at the highest amount of roAbeta the specific signal was reduced by approximately 95%. These studies suggest that (i) the presence of small amounts of roAbeta in huAbeta fibrils has the potential to cause subtle ultrastructural alterations in the polymers and (ii) the weak binding signal observed in vivo in the transgenic mouse models of AD may in part be due to the decreased number of high affinity binding sites on the Abeta fibrils.

Amyloid beta-Peptides↗
PubMed1991

The chemotherapy of rodent malaria. XLVI. Reversal of mefloquine resistance in rodent Plasmodium.

Multiple drug resistance in Plasmodium falciparum is already showing evidence of extending to mefloquine, which at present is one of the few alternative antimalarials for the prevention or treatment of infection with such parasites. Neither verapamil nor cyproheptadine, which reverse chloroquine (CQ) resistance in P. falciparum and in rodent malaria parasites, reverse resistance to mefloquine (MEF) in the MEF-resistant NS/1100 line of P. yoelii ssp. NS. On the other hand, such resistance is clearly reversed when mefloquine is administered to infected mice together with penfluridol.

Animals↗
PubMed1988

Species-specific response to the rodent carcinogens 1,2-dimethylhydrazine and 1,2-dibromo-3-chloropropane in rodent bone-marrow micronucleus assays.

1,2-Dimethylhydrazine is confirmed as active in the mouse bone-marrow micronucleus assay when administered as an aqueous solution via oral gavage to three different strains of mice. It is also shown to be inactive in a corresponding rat assay under similar conditions of test. The observations were independently repeated in two laboratories. In contrast, 1,2-dibromo-3-chloropropane showed the reverse profile, being active in the rat bone-marrow assay but inactive in the mouse; the latter observations were also made in two laboratories. The carcinogen procarbazine was active in both species. These findings are discussed within the context of the present GeneTox revision of the standard test protocol of the rodent bone-marrow micronucleus assay.

1,2-Dimethylhydrazine↗
PubMed1994

Guidelines for the welfare of animals in rodent protection tests. A report from the Rodent Protection Test Working Party.

The rodent protection test (RPT) is used in antimicrobial research to confirm the in vivo efficacy of novel antibacterial, antiviral and antifungal agents. The RPT may involve lethal infection and thus has the potential to cause significant suffering. These Guidelines recommend refinements to the RPT which reduce animal use to a minimum and suggest cardinal clinical signs which act as predictors of lethality. Early recognition of these signs is imperative to minimize suffering, allow identification of humane end points and permit timely euthanasia. Constructive suggestions for the improvement of these Guidelines are welcomed.

Animal Welfare↗
PubMed2002

The assessment of human health risks from rodent-borne diseases by means of ecological studies of rodent reservoirs.

Zoonoses in general, and more specifically rodent-borne diseases, have proven to be of increasing importance in recent decades. The study of vector biology, therefore, is the foundation for understanding the infection mechanisms for humans. Military operations on the European and Asian continent have been substantially affected by Hantavirus infections during World War I and World War II, the Korean War, and the more recent events in Bosnia. The recently discovered Hantavirus serotypes with high mortality may extend the risk for the future to North America. In this article, we focus on the host and ecosystem relationships that might be useful in predicting potential outbreaks in Western Europe.

Age Factors↗
PubMed1987

The mouse bioassay for the detection of estrogenic activity in rodent diets: II. Comparative estrogenic activity of purified, certified and standard open and closed formula rodent diets.

A major source of exogenous estrogenic substances, which may affect laboratory animals, comes from the diet. To test the possibility that commercially available rodent diets may significantly influence uterine weights and uterine:body weight (U:BW) ratios, estrogen bioassays were performed using female CD-1 mice weaned at 15 days of age and assigned randomly to a variety of commercial test diets or to a control diet (Purina #5002) containing 0 or 6 ppb added diethylstilbestrol (DES) for comparison. Mice were housed five per cage and given deionized water and feed ad libitum. Uterine:BW ratios from 15 mice per diet were determined after 3, 5 and 7 days of feeding. Mice fed The American Institute of Nutrition purified diet (AIN-76A) or the Purina #5015 natural ingredient breeder diet had significantly (P less than 0.05) increased U:BW ratios at 3, 5 and 7 days post weaning when compared to the control diet without added DES. This increase in U:BW ratios was similar to the U:BW ratios observed in a natural ingredient maintenance diet (Purina #5002), containing 6 ppb of DES. These results show that significant differences exist in the level of substances which can cause increase in uterine weight in some commercial diets. The diet may be important when performing or comparing certain types of studies, especially those relating to estrogenic substances. A standardized diet with minimal estrogenic activity may be desirable for such studies. It is unclear from the present studies what substances might be responsible for the uterine growth promoting activity in the diets examined.

Animal Feed↗
PubMed1984

The chemotherapy of rodent malaria, XXXVIII. Studies on the activity of three new antimalarials (WR 194,965, WR 228,258 and WR 225,448) against rodent and human malaria parasites (Plasmodium berghei and P. falciparum).

In addition to their blood schizontocidal action on Plasmodium berghei in vivo, two Mannich bases WR 194,965 and 228,258 are also active against chloroquine-sensitive and chloroquine-resistant lines of P. falciparum in vitro. The response of the lines to each drug differs but shows no correlation in either case with response to chloroquine. The 8-aminoquinoline WR 225,448 is also active against P. falciparum in vitro but at much higher concentrations than the Mannich bases. Application of the 'chloroquine-induced pigment clumping (CIPC) test' and the study of ultrastructural changes induced in P. berghei in drug-treated mice indicate that WR 194,965 has a mode of action somewhat resembling that of quinine. WR 228,258 in vitro shows a chloroquine-like effect, but not in vivo, suggesting that its mode of action in vivo is different from that of chloroquine. WR 225,448 has no action in the CIPC in vitro and affects primarily mitochondria of the parasites in vivo. It probably acts through a metabolite. Both pre-erythrocytic and erythrocytic stages of rodent malaria parasites are affected by WR 225,448.

Aminoquinolines↗
PubMed2004

Prospective studies of Bartonella of rodents. Part II. Diverse infections in a single rodent community.

The genetic diversity of Bartonella species within a small mammal community and in individual cotton rats (Sigmodon hispidus) was examined by trapping, capturing, sampling, and releasing of marked animals over a 17-month interval. Based on sequence analyses of the Bartonella gltA gene, amplicons separated into four genogroups (A, B, C, and Pin) containing 11 variants. Although the prevalence of bacteremia due to different genogroups/variants of Bartonella was temporally variable, variants of genogroup A predominated during each sampling period. Multiple gltA variants were often (20.5% of individuals) isolated from a single cotton rat blood sample; a maximum of five variants was recovered from an individual during its sampling history. Among 92 cotton rats bacteremic at two or more sampling dates, 34 rats retained a single genetic variant, alone or in mixed infection, throughout their sampling history. The temporal course of individual infections was complex as the succession of gltA variants was variable and detectable bacteremia was often intermittent. No antibodies (titer of >1:8) were detected to homologous strains of Bartonella recovered from individual cotton rats during their sampling history. The temporal course of Bartonella infections could result from a single, persistent, and potentially multi-genogroup/variant infection, during which variants differentially dominate the detectable bacteremia.

Animals↗