Thermographic monitoring of nests of nude mice in their early life: technical note

In this paper IRT (Infrared Thermographic Technique) has provided clear and replicable data about the surface temperature from the first hours of life until 5 days after birth of pups athymic Nude-Foxn1nu (nu/nu and nu/+). We initially hypothesized to use IRT to detect the phenotype of the pups from the very first hours of life, thinking that the presence (in mice nu/+) or absence (in mice nu/nu) of hair follicles could shield or less part of the emitted radiation. The experimental phase of three months was carried out at the IRCCS Istituto "Mario Negri" in Milan, in compliance with institutional guidelines and international laws. Were used: Mice: 3 females Hsd: Nude-Foxn1nu athymic (nu/+) 6 weeks of age and 3 males Hsd: Nude-Foxn1nu athymic (nu/nu) 6 weeks of age; Cages: 3 IVC ventilated under positive pressure, at 75 air changes hour; Litter: Animal Bedding autoclaved. Usually the litter is changed every two weeks; Food: Global Diet Harlan. Administration ad libitum; Water: autoclaved. Administration ad libitum. Hood Laminar Flow: CS5 changing station. Thermographic measurements are conducted 2 times per day (10:00 and 14:00). Per nest (mice 0-5 days) we sample 40 images taken in 10 minutes (one image every 15 seconds). For each shot the camera detects two image formats: ".IRI" (thermography) and ".JPEG" (visible) as a control. The instrument display allows to see in real time the quality of the thermographic image. We preferred to make the filming manually (the camera weight about 2 kg). Statistical analysis was performed on the same pool of pups but in a different ages. In the absence of effective thermogenic processes, the differences recorded between the two groups can be attributed to body size. Considering that the surface area decreases with increasing body weight and the heat loss per unit area is approximately constant and independent of the size and stature of the subjects in comparison, metabolic rate normalized to body weight decrease with increasing body weight the biggest-oldest pups lose less heat than littermates. The temperature of the nests (huddle) is very susceptible to the ambient temperature, to the presence of bedding and nest material. The physiological thermoregulation (BAT activity) and behavioral thermoregulation (huddling) do not allow autonomy thermoregulatory but help to slow the dissipation heat; the only way that the pups of 0-5 days of life can increase their body temperature is the transmission of heat from parents.