Non-invasive health monitoring methods for LPS experiments.

Lipopolysaccharides (LPS) are endotoxins causing systemic inflammation often used to experimentally mimic bacterial infections. Depending on the dose, injection of LPS can lead to reduced activity, hypothermia, sepsis, or even death. Non-invasive health monitoring methods are needed to correctly assess the severity and to take appropriate measures to minimize the burden. In our study, 56 female C75BL/6J mice were divided into two batches, each with two social groups. Mice were injected on four consecutive days. 19 mice received a total of four injections of 0.5 mg/kg LPS (LPS4) and 18 mice

received LPS only on the first day (LPS1). On the remaining three days they received DPBS, as did the 19 control animals (CON) on all four days. One aim was to determine the burden of LPS injection based on physiological and behavioral parameters. For this purpose, weight data collected daily before each LPS injection were analyzed. The data showed a significant difference between the groups. The LPS4 mice lost significantly more weight than the LPS1 and control mice. However, the LPS1 mice also lost significantly more weight than the control mice. One week after the injections, weight differences had disappeared. As an additional physiological parameter, temperature of the ocular surface was measured by thermography. The temperature was measured daily immediately after LPS injection (0h) and after 4, 8, and 24 hours. The use of a handling tube reduced the stress on the mice, as the mouse did not need to be restrained by hand. Furthermore, a sickness score was assessed and home-cage
activity was measured before, during and after the injection using an RFID-based system. Overall using a multimodal analysis of sickness behavior will contribute to optimizing the severity assessment of animal experiments.