Laboratory-bred Rats Research Articles

Development and Evaluation of Wild-Derived Rats as Potential Experimental Models for Research

Wild rodents have been used as animal models in experimental studies of cellular aging, cerebral malaria, schistosomiasis, and leishmaniasis. Since they are the reservoirs of these diseases, recent studies have shown that research involving wild rodents is more efficient in giving a mirror image of the disease progression outside the laboratory setting. The study design was an analytic experimental study where observations were made between two groups of animals i.e. the wild-derived and lab-bred rats. The outcome of the intervention was obtained by comparing the two groups. This study sought to determine the usability of wild-derived rats as potential experimental animal models for biomedical research. Wild rats were randomly captured in areas with high transmission of Schistosoma mansoni and Leishmania donovani in Kisumu and Kitui counties, in Kenya and maintained in the animal house at Kenya Medical Research Institute (KEMRI) in Nairobi. Breeding was carried out, and the subsequent generations were used to assess schistosomiasis and leishmaniasis disease progression between the wild-derived, and laboratory-bred rats. We further monitored behavior patterns and food consumption rate for 3 months in a total of 6 experimental trials. The results on feed consumption capacity indicated that consumption was significantly higher in laboratory-bred groups (p=0.001) compared to wild-derived rats. Overall, laboratory-bred rats were significantly heavier than wild rats. In the use of rats to assess schistosomiasis and leishmaniasis disease progression, the wild-derived rats were more susceptible to leishmaniasis and may be considered for S. mansoni compared to wild (worms recovered p=0.031). In conclusion, the study indicated that wild rats are potential reservoir hosts for both schistosomiasis and leishmaniasis and have the potential to maintain cycles of infection until after successful chemotherapeutic intervention. Therefore, wild rats may provide natural means for parasites like S. mansoni and L. donovani to re-infect humans in endemic areas.

Do individual differences in behavior influence wild rodents more than predation risk?

Prey can enhance their survival by eliciting an appropriate response to predators. Theoretically, prey should distinguish odors of predators and nonpredators. The manifestation of defensive antipredator behaviors has been extensively researched in domestic species (i.e., the relationship between laboratory-bred rats and domestic cats). However, little is known about the expression of these behaviors in wild rodents. Studies have so far focused on quantitative assessments of cost–benefit trade-offs or giving-up densities. We examined the expression of fine-scale defensive behaviors in Arnhem rock rats (Zyzomys maini) in response to fecal cues from 2 predators (the northern quoll [Dasyurus hallucatus] and the dingo [Canis dingo]), a nonpredator (the short-eared rock-wallaby [Petrogale brachyotis]), and a control (water). We adapted a predator-odor avoidance apparatus that has been widely used for domestic rodent studies to film the behavior of wild rock rats in a captive environment. Rock rats did not alter their behavior in the presence of odors of nonpredators, predators, or controls. In the current study, individual rock rats behaved in a consistent manner across time, and we identified 3 individually consistent behaviors which may suggest the existence of personality traits in this species. We suggest that these individual differences may influence wild rock rat behavior more than predation risk. These differences should therefore be taken into consideration when investigating behavioral responses to predators in wild populations.

Responders and nonresponders to cat odor do not differ in other tests of anxiety

Laboratory-bred rats can be divided into those showing clear innate behavioral responses to the odor of a predator (a cat) and those showing no response. However, these two groups did not differ in their responses to a neutral odor, or in the social interaction or elevated plus-maze tests of anxiety. This suggests a distinction between phobic anxiety (generated byt odor) and a generalized anxiety state (generated by novelty in the other test)). Trial 2 in the plus-maze generates a state of fear that is distinct from thet generated on trial 1, and one suggested to reflect phobic anxiety. Although the groups of cat responders and nonresponders did not differ in their scores on trial 2 in the plus-maze, two clear groups of responders and nonresponders could be identified on this trial 1 or not on trial 1 or in the social interaction test). This suggests that is possible to identify bimodal populations of rats in tests of both innate and acquired simple phobias.

The Wistar Rat as a right choice: establishing mammalian standards and the ideal of a standardized mammal.

In summary, the creation and maintenance of the Wistar Rats as standardized animals can be attributed to the breeding work of Helen Dean King, coupled with the management and husbandry methods of Milton Greenman and Louise Duhring, and with supporting documentation provided by Henry Donaldson. The widespread use of the Wistar Rats, however, is a function of the ingenuity of Milton Greenman who saw in them a way for a small institution to provide service to science. Greenman's rhetoric, as captured in his Director's Reports, prepared annually from 1905 until his death in 1937, shows that he was unusually sensitive to his times and to the economics of science and of society. In the era when biology was being defined, he recognized in the rat the potential to be a living analog to the pure chemicals that legitimated experimental science. From management literature he extracted the ideals of uniformity of product, standards of quality, and efficiency of production, applying them to scientific practice to generate an animal model that thrives as standard equipment in laboratories throughout the world today. I will close with a quote from Frederick W. Taylor that is a cogent statement of the contribution to science and scientific progress made by standardized tools and their creators. Equating the surgeon and the workman, Taylor wrote: [He is given] the finest implements, each one of which has been the subject of special study and development ... [and] the very best knowledge of his predecessors; and, provided with standard implements and methods which represent the best knowledge of the world up to date, he is able to use his own originality and ingenuity to make real additions to the world's knowledge, instead of reinventing things which are old. Standardized tools, whether surgeons' implements or laboratory-bred rats, are one of the vehicles for carrying scientific knowledge forward from generation to generation. In this sense, Greenman's Wistar Rats have done their job, in his words, of “providing service to science.”

Angiostrongylus costaricensis natural infection in Vaginulus plebeius in Nicaragua.

A study of 94 slugs, collected from urban and rural areas in and around Léon, Nicaragua, was carried out in order to confirm the role of Vaginulus plebeius as an intermediate host of Angiostronglylus costaricensis. Third-stage larvae of A. costaricensis were obtained from these molluscs. Some of these larvae were then orally inoculated into two laboratory-bred rats Sigmodon hispidus and adult worms of A. costaricensis were recovered two months later. The infection rate of these slugs ranged from 4% in urban areas to 85% in rural areas. These data suggest that contamination to man is a major risk especially in rural areas and that abdominal angiostrongyliasis could be a health problem in Nicaragua.

Role of early experience in social behaviour of laboratory-bred female rats

Social relationships among female laboratory-bred rats in a community are influenced by their early life history. When the rats were born and kept until adulthood under conventional breeding conditions, i.e. in single cages, and then used to form a community in which they gave birth, one female assumed the dominant role, with all others subordinate. The dominant female herded all young rats born in the community, irrespective of their age, in a single litter and suckled them. She accumulated food and wood shavings from other parts of the community near the nest and prevented access to the nest to all other community members including other females that had given birth. Subordinate females ceased to show maternal behaviour, including lactation, within 24 h (occasionally within 48 h). The mortality of the young until 15 days of age was high. This type of behaviour in a community was observed both with randomly chosen female rats and with rats selected as dominant and subordinate types in preceding experiments. Female rats born and reared in a community and rats living in a community from 15 to 30 days of age did not differentiate into dominant and subordinate types. All females retained their maternal behaviour, including lactation. Mortality of young rats was minimal. In most cases the females built one common nest; sometimes each female built her own nest. The results point to the decisive role of early experience in the development of maternal behaviour and in the occurrence of communal rearing of the young.

Lethal Factors in Experimental Infections of Trypanosoma equiperdum in Rats.

A biochemical and pathological study of experimental Trypanosoma equiperdum infections in laboratory-bred rats has disclosed that the animals died with a significantly reduced blood pH, lowered alkali reserve, and greatly diminished blood oxygen content, i. e., they finally succumbed to a condition of non-volatile, uncompensated acidosis. These findings are in harmony with the previously reported excessive lactic acid content and reduced oxygen content of the blood of trypanosome-infected rats (Kligler and Geiger;1 Kligler, Geiger and Comaroff2). A progressive hypoglycemia accompanied these terminal manifestations as has been demonstrated by a number of investigators.Tissue changes found at death were pronounced vasodilatation and congestion throughout the body, extreme enlargement of the spleen, varying degrees of pulmonary edema and occasionally emphysema, distension of the right heart and engorgement of the coronary vessels. The most significant development was the formation of intravascular blood clot...