Observational Evaluations of Mice during Cerebral Microdialysis for Pediatric Brain Tumor Research.

In vivo animal experiments are critical in the process of finding and developing new treatments for children with CNS tumors. Cerebral microdialysis, which enables researchers to measure drug concentrations in the brain or tumor tissue of unanesthetized mice, is a highly specialized procedure that provides valuable information that cannot be gained by using an in vitro system. When designing any in vivo animal study, 3 Rs principles (replacement, reduction, and refinement) must be considered to ensure that the highest standards of care are followed. As part of the refinement process, the objectives of this study were to collect behavioral monitoring data from mice undergoing cerebral microdialysis, to identify any behaviors predictive of significant pain or distress that could affect the animal's welfare, and to use these data to refine the existing monitoring checklist and schedule for its use by others performing this procedure. We developed a monitoring checklist for assessing wellbeing and distress of mice during cerebral microdialysis experiments. Comparison of 79 mice that underwent cerebral microdialysis experiments with a control group of 20 mice revealed that cerebral microdialysis and tethering of mice are well tolerated for as long as 24 h with only minor evidence of stress.

A mouse model for glucocorticoid-induced osteonecrosis: effect of a steroid holiday.

Glucocorticoid-induced osteonecrosis is a common and dose-limiting adverse event. The goal of this study was to establish a mouse model of glucocorticoid-induced osteonecrosis suitable for testing the effects of different treatment strategies on its frequency. Fourteen murine strains were screened using various glucocorticoids, routes of administration, and diets. Four-week-old male BALB/cJ mice were treated with oral dexamethasone for up to 12 weeks either by continuous dosing or by discontinuous dosing, with or without asparaginase. Histopathological features of the distal femurs were examined by light microscopy. Osteonecrotic lesions were characterized by empty lacunae and osteocyte ghosts in trabecular bone surrounded by necrotic marrow and edema. The incidence of dexamethasone induced osteonecrosis in BALB/cJ mice was 40-45% (4/10 or 5/11) at 12 weeks. The frequency of osteonecrosis trended lower after discontinuous compared to continuous dosing for 12 weeks (8 vs. 45%) (p = 0.06) despite comparable cumulative plasma exposure. Asparaginase hastened the occurrence of osteonecrosis, which was observed as early as 4 weeks and the incidence was 50% after 6 weeks. A mouse model of glucocorticoid-induced osteonecrosis was established. Discontinuous was less osteonecrotic than continuous dexamethasone treatment, consistent with the possible benefits of a "steroid holiday" seen in clinical settings. Moreover, asparaginase hastened osteonecrosis, indicating that drugs may interact with glucocorticoids to affect osteonecrosis risk.