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The reproducibility of pre-clinical research is an important concern that is now being voiced by constituencies that include the National Institutes of Health, the pharmaceutical industry, Congress, the public and the scientific community. An important facet of performing and publishing well-controlled reproducible pre-clinical research is to stabilize and more completely define the environment of the animal subjects. Scientists who use rodents in research generally recognize the importance of maintaining a stable animal environment. However, despite a theoretical and general awareness of these issues, many may lack a true appreciation of how significantly even seemingly minor variations in the environment can affect research outcomes. The purpose of this article is to help investigators gain a more comprehensive and substantiated understanding of the potentially significant impact of even seemingly minor environmental changes on the animals and the data. An important caveat to this article is that the examples presented were selected from a very large literature, admittedly in order to illustrate certain points. The goal of this article is not to provide an overview of the entire literature on how the environment affects rodents but rather to make preclinical scientists more aware of how these factors can potentially influence the experimental data and contribute to poor reproducibility of research., (Copyright © 2015. Published by Elsevier Inc.)

Problems with sleep affect a large part of the general population, with more than half of all people in the United States reporting difficulties with sleep or insufficient sleep at various times and about 40 million affected chronically. Sleep is a complex physiologic process that is influenced by many internal and environmental factors, and problems with sleep are often related to specific personal circumstances or are based on subjective reports from the affected person. Although human subjects are used widely in the study of sleep and sleep disorders, the study of animals has been invaluable in developing our understanding about the physiology of sleep and the underlying mechanisms of sleep disorders. Historically, the use of animals for the study of sleep disorders has arguably been most fruitful for the condition of narcolepsy, in which studies of dogs and mice revealed previously unsuspected mechanisms for this condition. The current overview considers animal models that have been used to study 4 of the most common human sleep disorders-insomnia, narcolepsy, restless legs syndrome, and sleep apnea-and summarizes considerations relevant to the use of animals for the study of sleep and sleep disorders. Animal-based research has been vital to the elucidation of mechanisms that underlie sleep, its regulation, and its disorders and undoubtedly will remain crucial for discovering and validating sleep mechanisms and testing interventions for sleep disorders.

Although genetic risk factors for influenza infection have not yet been defined in people, differences in genetic background and related variation in the response to infection, as well as viral virulence, are all likely to influence both the likelihood of infection and disease severity. However, apart from characterization of viral binding sites in avian and mammalian hosts, relatively little investigation has focused on host genetic determinants of susceptibility or resistance to infection, or the severity of the associated disease in humans or other species. Similarly, the role of genetic background in the generation of an efficacious immune response to either infection or vaccination has not been extensively evaluated. However, genetic influences on susceptibility and resistance to numerous infectious agents and on the resultant host inflammatory and immune responses are well established in both humans and other animals. Mouse-adapted strains of human influenza viruses and the use of inbred strains of laboratory mice have supported extensive characterization of the pathogenesis and immunology of influenza virus infections. Like individual humans, inbred strains of mice vary in their reactions to influenza infection, particularly with regard to the inflammatory response and disease severity, supporting the potential use of these mice as a valuable surrogate for human genetic variation. Relying heavily on what we have learned from mice, this overview summarizes existing animal, human and epidemiologic data suggestive of host genetic influences on influenza infection.

The frequent occurrence of fatigue and disturbed sleep in cancer survivors and the negative effect of these symptoms on quality of life and clinical outcome underscore the need to identify mechanisms that cause cancer-related fatigue, with a view toward developing more effective treatments for this problem. Human studies of fatigue and disturbed sleep are limited by high interindividual genetic and environmental variability, difficulties with behavioral or reporting compliance, and the subjective nature of the problems. Although animal models also must overcome the barrier of assessing fatigue and sleep disturbance in the absence of obvious objective clinical markers, animal studies are easier to control and standardize than are studies of people. Moreover, animal models are crucial to the identification and understanding of underlying disease mechanisms. This review describes the need for, the feasibility of, and several possible approaches to measuring fatigue in animal models of cancer and to relating such measures to disturbed sleep, immune function, and other potential mechanisms. Developing and using animal models to better understand fatigue and disturbed sleep related to cancer and its treatment has an enormous potential to expand the knowledge base and foster hypotheses necessary for the future development and testing of interventions.

Epstein-Barr virus (EBV) is a ubiquitous human gammaherpesvirus (GHV) that causes acute infection and establishes life-long latency. EBV is associated with the development of B-cell lymphoproliferative disorders, several malignant cancers, the syndrome of infectious mononucleosis, and chronic interstitial lung disease. Although the molecular biology of EBV has been characterized extensively, the associated disease conditions and their pathogenesis are difficult to study in human populations because of variation in human environments and genetics, the well-documented effect of stressors on pathogenesis, and the chronic and latent properties of the virus. GHV are highly species-specific, and suitable animal models for EBV are not available. However, in 1980, a murine gammaherpesvirus (MuGHV, also known as MHV68 and gammaHV68) was identified as a natural pathogen of bank voles and wood mice. Experimental MuGHV infections in laboratory mice share many features of EBV infections in humans, including facets of the clinical human syndrome known as infectious mononucleosis. These features make MuGHV a valuable experimental model for studying the pathophysiology of a GHV in a natural host.

Surgical implantation of devices into the abdomen of PL/J mice was associated with fatal hemorrhage at 9 to 11 d after surgery. Coagulation profiles were evaluated to determine the underlying cause of this effect. The mean activated partial thromboplastin time (aPTT) of untreated PL/J mice was significantly higher than that of BALB/cByJ and C57BL/6J strains. The addition of human plasmas deficient in factors VIII, XI, or XII, prekallikrein, or high molecular-weight kininogen corrected the elevated aPTT of PL/J mice, but correction did not occur when factor IX-deficient human plasma was added. When compared to an assigned factor IX activity of 100% for pooled plasma from BALB/cByJ mice, C57BL/6J and PL/J mice revealed percent activities of 67% and 16%, respectively. PL/J mice could represent a new model for the study of pathogenesis and therapy of mild factor IX deficiency that is expressed and becomes clinically apparent secondary to major surgery.

Sleep-wake disturbances are common in epilepsy, yet the potential adverse effect of seizures on sleep is not well characterized. Genetically epilepsy-prone rats (GEPRs) are a well-studied model of genetic susceptibility to audiogenic seizures. To assess their suitability for investigating relationships between seizures and disordered sleep, we characterized the sleep, activity, and tempera ture patterns of 2 GEPR strains (designated 3 and 9) and Sprague-Dawley (SD) rats in the basal state, after forced wakefulness, and after exposure to sound-induced seizures at light onset and dark onset. Because of observed differences in rapid-eye-movement sleep (REMS), we also assessed serum levels of prolactin, which is implicated in REMS regulation. The data reveal that under basal conditions, the GEPR3 strain shows less SWS and REMS, higher core temperatures, and higher serum prolactin concentrations than do GEPR9 and SD strains. All 3 strains respond similarly to enforced sleep loss. Seizures induced at light onset delay the onset of SWS in both GEPR strains. Seizures induced at dark onset do not significantly alter sleep. Genotype assessment indicates that although both GEPR strains are inbred (that is, homozygous at 107 genetic markers), they differ from each other at 74 of 107 loci. Differences in basal sleep, temperature, and prolactin between GEPR3 and GEPR9 strains suggest different homeostatic regulation of these functions. Our detection of concurrent alterations in sleep, temperature, and prolactin in these 2 GEPR strains implicates the hypothalamus as a likely site for anatomic or physiologic variation in the control of these homeostatic processes.

Human patients with renal disease frequently develop disturbed sleep and severe fatigue. To develop a model for studying factors that contribute to these symptoms, we characterized the sleep patterns of various strains of mice after acute challenge with the fungal organism Candida albicans. After intravenous administration to mice, C. albicans typically colonizes the kidney, producing acute pyelonephritis. Various strains of inbred mice demonstrate marked variation in the temperature and sleep responses that develop after challenge, with individual strains generally showing increased or reduced somnolence in association with fever or hypothermia, respectively. C. albicans-infected mice may be a useful model for identifying the genes and mechanisms that link sleep, temperature, fatigue, and the immune response.