Evaluation of the effects of chemotherapy-induced fatigue and pharmacological interventions in multiple mouse behavioral assays

Abstract

Fatigue is a common symptom in many diseases and disorders and can reduce quality of life, yet lacks an adequate pharmacological intervention. To identify and develop such interventions, and to better understand fatigue, additional preclinical research is necessary. However, despite numerous mouse behavioral assays reportedly detecting fatigue-like behavior, the assumption that fatigue-like behavior is detected in many assays has not been validated through a cross-assay study. Thus, we modeled fatigue in mice by administering 5-fluorouracil, a chemotherapy drug known to cause fatigue in humans and fatigue-like behavior in mice, then evaluated its effects via voluntary wheel running activity (VWRA), locomotor activity in the open field test (OFT), immobility in the forced swim test (FST), and distance run in the treadmill fatigue test (TFT) and treadmill exercise capacity test. Additionally, taltirelin or methylphenidate was administered to alleviate fatigue-like behavior. As a result of 5-fluorouracil treatment, VWRA and the TFT were markedly reduced, indicating fatigue. The OFT, FST, and treadmill exercise capacity test, however, failed to detect fatigue-like behavior. Interestingly, both taltirelin and methylphenidate alleviated fatigue-like behavior in TFT. These data suggest that, of the current assays, only the TFT and VWRA should be expected to detect fatigue-like behavior. Moreover, this study provides additional evidence that taltirelin may provide a novel treatment for chemotherapy-induced fatigue and warrants further evaluation as an anti-fatigue therapeutic.

Keywords: Exercise capacity; Fatigue model; Forced swim; Open field; Treadmill fatigue test; Wheel running.

Figure 1.. Timeline of experiments.

Experimental timelines for (A) voluntary wheel running activity, (B) open field and forced swim tests, and (C) treadmill exercise capacity and treadmill fatigue tests.

Figure 2.. Effects of chemotherapy on food consumption and body weight.

(A) Average food eaten during acclimation (“Acclimation”) and baseline (“Baseline”) phases in the VWRA experiment and food eaten on day 5 of the experiment (“Treatment”). (B) Body weight of mice in the VWRA experiment over the 5 days of 5-FU treatment. Data represent mean±SEM of 6–7 mice per group. ^**p < .01, ^***p < .001, ^****p < .0001, 5-FU-PBS vs PBS+PBS, ^ap > .05 compared to 5-FU+PBS, t-test with Holm-Bonferroni correction

Figure 3.. Effects of chemotherapy on voluntary wheel running activity.

VWRA at baseline (the mean of 4 days of wheel running after mice acclimated to the running wheels) and daily during the treatment period (day 1–6). Data represent mean±SEM of 6–7 mice per group. Data from the PBS+PBS and 5-FU+PBS groups were previously published and are reproduced with permission from [18]. *p < .05, ^**p < .01, ^****p < .0001, 5-FU+PBS vs PBS+PBS, t-test with Holm-Bonferroni correction

Figure 4.. Effects of chemotherapy and interventions on distance run in different treadmill tests.

Distance run by mice in the (A) treadmill exercise capacity test and (B) treadmill fatigue test. Data from the PBS+PBS and 5-FU+PBS groups in panel A were previously published and are reproduced with permission from [18]. Data represent the mean+SEM of 11–12 mice per group. ^**p < .01 compared to PBS+PBS, ^†p < .05, ^†††p < .001 compared to 5-FU+PBS, t-test with Holm-Bonferroni correction