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At least 145 records · Page 8Linked to original sources
PubMed1994

Historical histopathological control data for laboratory rodents: valuable treasure or worthless trash?

The reasons for variation in longevity and disease incidence in untreated control animals in chronic toxicity and carcinogenicity tests in laboratory rodents are reviewed and discussed. Genetic drift, dietary composition, caloric intake, age of animals at the termination of studies, the skill, experience and diligence of the pathologist, the diagnostic criteria used and the appropriateness of statistical procedures are considered to be the most important sources of variation. It is suggested that more attention needs to be paid to the sources of nutrients in animal diets and that 'closed formula' diets should be eschewed. The reliability of historical data depends critically on the extent to which 'like' can be compared with 'like'. The most important variables in relation to histopathological data are considered in this context.

Aging↗
PubMed1975

Evaluation of demographic parameters of native rodent populations and implications for control.

The ecology of the multimammate mouse ,Mastomys natalensis, is reviewed and approximations are derived for the parameters governing population growth. By means of computer simulation, the relative importance of the timing of reproduction, the age class distribution or age structure of the population, the competition between Mastomys and Rattus, and the interaction with a predator are evaluated. Although each of these demographic or ecological factors modifies the fate of the Mastomys population, the greatest single impact results from a reproductive season that is divided into two parts rather than a single continuous reproductive season. Division into two parts, correlated with a similar distribution of rainfall, allows time for maturing of the young born early in the season and for production of young by them, thus adding to the momentum of population increase. The interaction of density-dependent factors controlling population growth, competition with another rodent, or predation by a Viverrid predator, may increase the growth rate of the Mastomys population or may depress population growth rate, even to the point of extinction. These simulation studies demonstrate the necessity for critical evaluation of the demographic parameters and ecological characteristics of a particular Mastomys population before an effective control programme can be designed. They also demonstrate, however, that if the programme is based upon sound ecological theory control can be effected.

Africa↗
PubMed1991

The role of dominance and epistasis in the genetic control of blood pressure in rodent models of hypertension.

Genetic analyses of crosses between hypertensive rodent models and their normotensive controls were performed on 43 sets of data published between 1970-1989. In each case, the cross involved F1, F2, and both backcross generations for a "complete genetic cross." Biometrical analysis estimated genetic parameters and their standard errors associated with dominance and epistasis (interaction of alleles that are not at the same locus). The statistical significance of these parameters was determined by comparing the parameter to its standard error. A purely additive inheritance pattern was seldom found. Additive/dominance inheritance was apparent in only two models. The prevailing pattern of inheritance was one with partial dominance for alleles for normal blood pressures and epistatic interactions. Finding epistasis in so many models will have implications for the application of cosegregation and linkage analyses in hypertension research.

Animals↗
PubMed1983

In vitro growth control phenotypes of transformed rodent cells prior to and following tumorigenesis.

A number of virus and chemical carcinogen-transformed cell lines were generated in tissue culture and analyzed for growth control phenotypes prior to and following tumorigenesis in appropriate hosts. The cell lines include those of mouse, rat, human, and Syrian hamster, transformed by papovaviruses and adenoviruses (DNA) or murine (RNA) tumor viruses. Cell lines were assayed for: (a) multinucleation or uncontrolled nuclear division (UND+) and uncontrolled DNA synthesis in cytochalasin B (CB) medium; and (b) the continuation of DNA synthesis in media containing reduced (0.5%) amounts of serum. All or nearly all lines of DNA virus transformants exhibited UND+ and high frequencies of DNA-synthetic cells in CB medium. Two lines of SV40-transformed hamster cells also showed UND+ following tumorigenesis in weaning hamsters. In addition, DNA virus transformants showed the ability to continue DNA synthesis unabated in low-serum medium. In contrast, the mouse sarcoma virus (MSV)-transformed lines exhibited varying degrees of controlled nuclear division and reduced DNA synthesis in CB medium, both prior to and following tumorigenesis. However, the reduction in DNA-synthetic cells was often not as great as that found in untransformed cells. Results similar to the RNA virus transformants were observed with hamster cells transformed by chemical carcinogens. Nearly all of the MSV-transformed lines showed significantly reduced levels of DNA synthesis in low-serum medium as was found in untransformed cells. One cell line, KA31, was followed through three consecutive in vivo tumorigenic passages, but these cells did not acquire UND+ or the ability to continue DNA synthesis in low-serum medium. These results suggest that many MSV- and carcinogen-transformed rodent cells exhibit transformation phenotypes at levels barely above those of normal cells and markedly less than those of DNA virus transformants, and yet they are tumorigenic.

Animals↗
PubMed1995

Localization of substance P receptors in central neural structures controlling daily rhythms in nocturnal rodents.

Brain areas involved in the genesis and control of daily rhythms receive a prominent neural input that contains the neurotransmitter substance P (SP), a peptide putatively involved in the synchronization of circadian rhythms by environmental light. We investigated the localization of receptors to SP in the suprachiasmatic nucleus of the hypothalamus (SCN) and in the intergeniculate leaflet of the thalamus (IGL) of the rat and hamster using in situ hybridization histochemistry and immunohistochemistry. Consistently with that previously described in the rat, a neuronal population distributed along the lateral margin and at the dorso-latero-caudal aspect of the hamster SCN expresses moderately the mRNA encoding the SP receptor. In both rat and hamster, immunohistochemical data confirm the previous finding and reveal an almost complete absence of SP receptors in the ventral part of the SCN, which receives a direct projection from the retina. In the IGL of both species, numerous neurons prominently express the mRNA encoding the SP receptor. The immunostaining shows a high density of SP receptors on perikarya and dendrites throughout the nucleus. A dense staining is also observed on individual cells and processes bordering the lumen of blood vessels in the SCN and IGL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Effect of chronic feeding of ethanol diet of "average" fat content on rat pancreas.

The present study was done to determine the influence of dietary fat on the effect of ethanol on pancreatic macromolecular content and secretion. Weight-matched groups of Sprague-Dawley rats were divided into controls fed Rodent-Blox ad libitum; American Institute of Nutrition-76 (AIN-76) diet containing 12% calories as fat with 36% of carbohydrate calories replaced with 5% (weight/volume) concentration of ethanol fed ad libitum pair fed with animals given isocaloric amounts of AIN-76 diet for three to six months. Compared with Rodent-Blox fed controls, tissue content of trypsinogen, chymotrypsinogen, amylase, and lipase; specific activity and concentration of trypsinogen, chymotrypsinogen; and concentration of amylase were decreased at six months in AIN-76 fed controls. These changes did not result from diminished food intake, but were due to adaptation to the liquid diet. Animals fed AIN-76 diet plus ethanol did not show significant difference in the total content, specific activity, concentration, and secretion of digestive enzymes compared with those animals pair fed isocaloric amounts of AIN-76 diet. Activation of trypsinogen by exogenous trypsin was lower in rats fed AIN-76 diet and a similar change was observed in animals fed AIN-76 diet with ethanol for six months. These findings are in contrast to increased secretion of proteases and decreased trypsin inhibitor observed previously in animals fed ethanol in a diet containing "high" fat. These data indicate that ethanol effect on the pancreas is modified by dietary intake of fat and/or carbohydrates.

Amylases↗
PubMedDate not supplied

Effect of Glyzophrol on fertility of female black rats (Rattus rattus).

Mild degree of fibrosis, dilatation of blood vessels, haemorrhagic reactions in a few places, granulosa cells in stroma and no effect on maturation process of follicles were observed in ovary of 20 mg/kg of Glyzophrol treated rats. After 60 mg/kg of Glyzophrol treatment, ovary revealed reduction in number of follicles, degenerative changes in existing follicles, frequent proliferation of granulosa cells and fibrosis in stroma along with karyorrhexis, karyolysis and pyknosis in nuclei. Haemorrhage and dilated blood vessels in stroma were well marked, suggesting that ovarian vasculature was affected by glyzophrol. Ovary exhibited increase in activity of acid phosphatase after Glyzophrol treatment. Intense alkaline phosphatase activity was observed in entire ovarian tissue after Glyzophrol treatment.

Acid Phosphatase↗