Small Animal MRI.

KEY WORDS: animal model; magnetic resonance imaging; thiamine deficiency; brain damage; AOD abstinence; AODE (alcohol and other drug effects) AIcoholism and other diseases affect the structure and function of many organs in the human body, including the brain. To understand the causes and to diagnose and track the progress of such diseases, scientists must understand the structural and functional changes in the affected organs. For many studies, particularly those involving the brain, researchers rely on noninvasive methods to visualize the organ under investigation. One technique commonly used to obtain images of a patient's brain or other area of the body is magnetic resonance imaging (MRI). This technique exposes the subject to radio waves in the presence of a strong magnetic field and then measures how the atoms that make up the body's tissues absorb the radio waves' energy. The manner of absorption varies, depending on the composition of the tissues (e.g., their water or fat content); with the help of computers, these variations can be converted into images. This article describes how MRI technology can be used not only on human patients but also in studies of laboratory animals that frequently serve as experimental models for human diseases. Also presented are findings of MRI studies that analyzed the effects of thiamine deficiency--the lack of a vitamin required for normal brain functioning--on the brain structure of rats. Preliminary findings indicate that similar studies can be used to assess the effects of long-term alcohol consumption and withdrawal on the brain. Although MRI has been used successfully in humans to diagnose diseases and study alterations in organ structures, its applications in elucidating the cause of a pathology or functional abnormality are more limited. To investigate the cause of a disease, researchers ideally would compare images of patients taken before and after they develop the disorder. Only rarely, however, do patients have images available for comparison that were taken prior to an illness. Alternatively, investigators can compare one group of subjects with a disease (e.g., alcoholics) with another group of people without the disease (e.g., nonalcoholics) to identify consistent differences between the two groups that might shed light on the cause of alcoholism. The subjects in such studies, however, will have different characteristics in addition to their alcohol intake (e.g., their medical and drinking histories and their genetic makeup). To make valid observations and to control for all possible variations among subjects, researchers must examine a large number of patients before attributing specific differences between the two study groups to alcohol use. Because of these limitations of human studies, researchers frequently rely on animal models, often using rats and other small animals. In general, animal studies provide more consistent information with fewer subjects than do human studies. The animals can be examined both before and after they develop a certain disease or undergo a particular treatment. Furthermore, animal studies can be rigidly controlled so that a particular change in organ structure or function can be directly attributed to the modification of a single experimental variable. Differences between animals can be minimized by using animals from one family (i.e., strain), a method that in humans would be feasible only with identical twins. And in contrast to studies on humans, studies using animals can be conducted across an animal's life span (about 2.5 years for rats), allowing the investigation of age-related effects. Conventional Techniques Histological techniques (i.e., studies that determine the structure of organs by examining thin tissue slices under a microscope) are commonly used to follow disease development in animals. Although these techniques allow researchers to view directly the tissue under investigation, they have several drawbacks, especially in studies of the brain. …