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

Non-Invasive Assessment of Mild Stress-Induced Hyperthermia by Infrared Thermography in Laboratory Mice

“…Duparcq et al, [ 37 ] observed that the maximum eye temperature peaked within 1 min, while tail temperature dropped to its lowest at around 2 min after exposure to a novel environment. Drop in tail temperature lasting for at least 2 min was observed also in our study, with this short-term vasoconstriction resulting in reduction of heat dissipated through the tail surface [ 22 ]. This initial drop in temperature can, during prolonged stress exposure, be followed by an increase in tail temperature [ 17 ], as a means to dissipate excess heat [ 22 ].…”

“…Drop in tail temperature lasting for at least 2 min was observed also in our study, with this short-term vasoconstriction resulting in reduction of heat dissipated through the tail surface [ 22 ]. This initial drop in temperature can, during prolonged stress exposure, be followed by an increase in tail temperature [ 17 ], as a means to dissipate excess heat [ 22 ]. We believe that the increase in T tail of the third animal tested during the DH test provides support for this explanation.…”

“…SIH in laboratory rodents causes an increase in body and eye temperature, while temperature in the extremities, such as in the tail and paws, tends to decrease [ 18 , 20 ]. These contrasting responses during acute stress exposure are mostly mediated by either vasodilation or vasoconstriction regulating blood flow into the different body regions, each representing a ‘thermal window’ that offers specific information for the understanding of the general physiological response [ 21 , 22 , 23 ]. For laboratory animals, the tail, ocular, auricular and interscapular regions are the most commonly observed thermal windows [ 22 ].…”

“…These contrasting responses during acute stress exposure are mostly mediated by either vasodilation or vasoconstriction regulating blood flow into the different body regions, each representing a ‘thermal window’ that offers specific information for the understanding of the general physiological response [ 21 , 22 , 23 ]. For laboratory animals, the tail, ocular, auricular and interscapular regions are the most commonly observed thermal windows [ 22 ]. Eye temperature has been proposed as the closest approximation to core temperature [ 24 ].…”

Transient Receptor Potential (TRP) and Thermoregulation in Animals: Structural Biology and Neurophysiological Aspects

“…Identifying between-species differences and determining the thermal comfort ranges of specific animal species is mediated by neurons in the central nervous system (CNS) and peripheral receptors [ 15 , 16 ]. Thermosensitive receptors exist in both prokaryotic and eukaryotic organisms [ 17 ].…”