Research on Experimental Animal Models (In Vivo)
| In vivo research is conducted on the whole animal. Over the years a variety of experimental animal models, such as yeasts, zebra fish, nematodes and fruit flies (Drosophila) were developed for research, on which a wealth of information has accumulated. Research on mammals is generally conducted on rat and mouse models, and to a lesser degree on pigs and monkeys. |
Research on mause in the laboratory |
In vivo studies explore the association between environmental exposure to a potential hazardous factor (risk factor) and development of a disease such as cancer (the outcome). In such experiments, the observed biological phenomena taking place in a group of animals exposed to the potential risk factor (experimental group) are compared with those observed in an identical group of animals that was not exposed to the studied factor (control group). Analysis of the results is based on comparing the proportion (percentage) of animals that developed the biological phenomena in the experimental group with that of the control group. If statistically significant differences are observed between the two groups regarding the development of the biological phenomena, the existence of an association between exposure to the potential risk factor and development of the disease may be assumed. In most studies the experimental (exposed) group is further divided into sub-groups according to the exposure level. A biological effect that changes according to the strength or intensity of exposure to the potential hazardous factor, creating a dose-response curve, can support the hypothesis regarding the effect of that variable on the observed outcomes.
In order to obtain statistically significant results, a sufficient number of animals in the experimental group must show signs of the biological phenomenon. To ensure this, often animal models that have a greater likelihood of developing the biological phenomenon studied are chosen; for example, a mouse model that has an increased risk of developing cancer or other diseases (due to a deliberate change to their genome). In such animals it will be easier to assess whether the studied risk factor does in fact increase the probability of developing the disease.
Other animal models simulate a human disease condition. In such an experimental model, animals affected with the disease, or showing physiological signs resembling those of the disease in humans, are used. This method enables studying how the disease develops, factors that influence its progression, and the effectiveness of drugs to treat it.
Over the past 30 years numerous animal studies have been conducted, mainly on rat and mouse models, to reveal the effect of non-ionizing radiation on living organisms. These studies were aimed at understanding if non-ionizing radiation is a risk factor in the development of various disease conditions, such as cancer, neurological diseases, infertility, etc.
Like in vitro studies, in vivo research enables the control of various parameters assessed in the experiment (such as level of radiation), and the collection of selective data on the response of the animals to different levels of exposure.
However, the results of experiments on animals cannot always predict outcomes in humans under similar conditions of exposure. This disparity is due both to physiological differences between humans and other living organisms, and to limitations of planning and execution of the research. For example, researchers often use any available model, and not necessarily the most suitable animal for investigation of the problem they wish to examine. There are sometimes objective difficulties in the ability to recreate the disease condition exactly in the model, such as in cases where the experimental animal does not possess the same biological mechanism that gave rise to the disease, or in cases of a disease caused by a number of factors acting simultaneously in the body. As a result, the findings obtained in such experiments may give only a partial or inexact answer to the research hypothesis.
Pharmaceutical companies also struggle with the issue of the disparity between the results of animal experiments and those of clinical research. In a large proportion of cases, significant effects of drugs observed in animal models cannot be translated to a clinical outcome in humans. In the field of non-ionizing radiation research there is an additional challenge in planning the experimental environment, since the type and duration of exposure to radiation in the laboratory must simulate the conditions of 'real-life' human exposure.
