Experimental Applications and Factors Involved in Validating Thermal Windows Using Infrared Thermography to Assess the Health and Thermostability of Laboratory Animals

SIMPLE SUMMARY: Laboratory animals are fundamental in biomedical science and monitoring their health and metabolic processes is essential to ensure their welfare and the quality of the research conducted. Infrared thermography (IRT) is a tool that can assess pathological or stressful states by measuring changes in the amount of heat that bodies dissipate. To date, some thermal windows have been utilized to evaluate animals’ thermoregulatory capacity, such as the orbital region, the auricle or ear pavilion region, the tail, and the interscapular zone where brown adipose tissue (BAT) is stored. However, the sensitivity and specificity of these windows are still subject to controversy because the scientific evidence that is available differs regarding the thermal information reported. Therefore, this paper aims to discuss the neurophysiological mechanisms of the vasomotor and thermogenesis responses (using BAT) in laboratory animals, the scientific usefulness of IRT, and the various thermal windows that are currently being used with laboratory animals. ABSTRACT: Evaluating laboratory animals’ health and thermostability are fundamental components of all experimental designs. Alterations in either one of these parameters have been shown to trigger physiological changes that can compromise the welfare of the species and the replicability and robustness of the results obtained. Due to the nature and complexity of evaluating and managing the species involved in research protocols, non-invasive tools such as infrared thermography (IRT) have been adopted to quantify these parameters without altering them or inducing stress responses in the animals. IRT technology makes it possible to quantify changes in surface temperatures that are derived from alterations in blood flow that can result from inflammatory, stressful, or pathological processes; changes can be measured in diverse regions, called thermal windows, according to their specific characteristics. The principal body regions that were employed for this purpose in laboratory animals were the orbital zone (regio orbitalis), auricular pavilion (regio auricularis), tail (cauda), and the interscapular area (regio scapularis). However, depending on the species and certain external factors, the sensitivity and specificity of these windows are still subject to controversy due to contradictory results published in the available literature. For these reasons, the objectives of the present review are to discuss the neurophysiological mechanisms involved in vasomotor responses and thermogenesis via BAT in laboratory animals and to evaluate the scientific usefulness of IRT and the thermal windows that are currently used in research involving laboratory animals.