Determination of Postmortem Interval in Mice

Despite the major use of mice in biomedical research, little information is available with regard to identifying their postmortem changes and using that information to determine the postmortem interval (PMI), defined as the time after death. Both PMI and environmental conditions influence decomposition (autolysis and putrefaction) and other postmortem changes. Severe decomposition compromises lesion interpretation and disease detection and wastes limited pathology resources. The goal of this study was to assess postmortem changes in mice in room temperature cage conditions and under refrigeration at 4 °C to develop gross criteria for the potential value of further gross and histologic evaluation. We used 108 experimentally naïve C57BL/6 mice that were humanely euthanized and then allocated them into 2 experimental groups for evaluation of postmortem change: room temperature (20 to 22 °C) or refrigeration (4 °C). PMI assessments, including gross changes and histologic scoring, were performed at hours 0, 4, 8, and 12 and on days 1 to 14. Factors such as temperature, humidity, ammonia in the cage, and weight change were also documented. Our data indicates that carcasses held at room temperature decomposed faster than refrigerated carcasses. For most tissues, decomposition was evident by 12 h at room temperature as compared with 5 d under refrigeration. At room temperature, gross changes were present by day 2 as compared with day 7 under refrigeration. Mice at room temperature lost 0.78% of their baseline body weight per day as compared with 0.06% for refrigerated mice (95% CI for difference 0.67% to 0.76%, P < 0.0005). This study supports the consideration of temperature and PMI as important factors affecting the suitability of postmortem tissues for gross and histologic evaluation and indicates that storage of carcasses under refrigeration will significantly slow autolysis.

Polyomavirus-associated Disseminated T-cell Lymphoma in a Colony of Zebra Finches (Taeniopygia guttata)

Four zebra finches in a closed research colony presented with variable clinical signs, including masses, skin lesions, shivering, and/or ruffled feathers. These birds were not responsive to treatment efforts; 3 died and one was euthanized. All 4 were submitted for necropsy to determine the cause of the clinical signs. Gross necropsy and histopathologic findings from all birds resulted in a diagnosis of round cell neoplasia in multiple organs, including the skin, liver, kidney, and reproductive tract, with intranuclear inclusion bodies in the neoplastic cells. In all 4 cases, immunohistochemical staining showed strong immunoreactivity for CD3 in 70% to 80% of the neoplastic round cells, with a relatively small subset that were immunopositive for Pax5. These findings supported a diagnosis of T-cell lymphoma. Frozen liver tissue from one case was submitted for next-generation sequencing (NGS), which revealed viral RNA with 100% sequence homology to canary polyomavirus strain 34639 that had originally been identified in a European goldfinch. Formalin-fixed paraffin-embedded scrolls from another case were also submitted for NGS, which revealed viral RNA with 97.2% sequence homology to canary polyomavirus strain 37273 that had originally been identified in a canary. To localize the virus in situ, RNAscope hybridization was performed using a probe designed to target the VP1 gene of the sequenced virus in frozen liver tissue. In all 4 cases, disseminated and robust hybridization signals were detected in neoplastic cells. These findings indicate that polyomaviruses have the potential to be oncogenic in zebra finches.

Polyomavirus-associated Disseminated T-cell Lymphoma in a Colony of Zebra Finches (Taeniopygia guttata)

Four zebra finches in a closed research colony presented with variable clinical signs, including masses, skin lesions,shivering, and/or ruffled feathers. These birds were not responsive to treatment efforts; 3 died and one was euthanized. All4 were submitted for necropsy to determine the cause of the clinical signs. Gross necropsy and histopathologic findings fromall birds resulted in a diagnosis of round cell neoplasia in multiple organs, including the skin, liver, kidney, and reproductivetract, with intranuclear inclusion bodies in the neoplastic cells. In all 4 cases, immunohistochemical staining showed strongimmunoreactivity for CD3 in 70% to 80% of the neoplastic round cells, with a relatively small subset that were immunopositivefor Pax5. These findings supported a diagnosis of T-cell lymphoma. Frozen liver tissue from one case was submittedfor next-generation sequencing (NGS), which revealed viral RNA with 100% sequence homology to canary polyomavirusstrain 34639 that had originally been identified in a European goldfinch. Formalin-fixed paraffin-embedded scrolls fromanother case were also submitted for NGS, which revealed viral RNA with 97.2% sequence homology to canary polyomavirusstrain 37273 that had originally been identified in a canary. To localize the virus in situ, RNAscope hybridizationwas performed using a probe designed to target the VP1 gene of the sequenced virus in frozen liver tissue. In all 4 cases,disseminated and robust hybridization signals were detected in neoplastic cells. These findings indicate that polyomaviruseshave the potential to be oncogenic in zebra finches.

Vascular endothelial growth factor associated dissimilar cerebrovascular phenotypes in two different mouse models of Alzheimer's Disease

Vascular perturbations and cerebral hypometabolism are emerging as important components of Alzheimer's disease (AD). While various in vivo imaging modalities have been designed to detect changes of cerebral perfusion and metabolism in AD patients and animal models, study results were often heterogenous with respect to imaging techniques and animal models. We therefore evaluated cerebral perfusion and glucose metabolism of two popular transgenic AD mouse strains, TgCRND8 and 5xFAD, at 7 and 12 months-of-age under identical conditions and analyzed possible molecular mechanisms underlying heterogeneous cerebrovascular phenotypes. Results revealed disparate findings in these two strains, displaying important aspects of AD progression. TgCRND8 mice showed significantly decreased cerebral blood flow and glucose metabolism with unchanged cerebral blood volume (CBV) at 12 months-of-age whereas 5xFAD mice showed unaltered glucose metabolism with significant increase in CBV at 12 months-of-age and a biphasic pattern of early hypoperfusion followed by a rebound to normal cerebral blood flow in late disease. Finally, immunoblotting assays suggested that VEGF dependent vascular tone change may restore normoperfusion and increase CBV in 5xFAD.

Comparison of Four Beddings for Ammonia Control in Individually Ventilated Mouse Cages

Ammonia control is an important characteristic of rodent bedding materials. Among natural bedding materials, corncob bedding provides excellent ammonia control but contains estrogenic compounds and is ingested by mice. By comparison, processed cellulose bedding products are biologically inert and harbor fewer bacteria but historically have shown low absorbency or poor ammonia control. New cellulose products have been developed to address these shortcomings. Over a 2-wk period, we evaluated intracage ammonia levels in mouse IVC using 4 bedding types: shaved aspen, corncob, virgin pelleted cellulose, and refined virgin diced cellulose. Ammonia levels were measured by using 3 methods: colored reagent tubes, colorimetric paper strips, and a photoionization detector. Corncob, pelleted cellulose, and diced cellulose showed better ammonia control than aspen as early as 4 d after cage changing and throughout the 2-wk measurement period. In addition, pelleted and diced cellulose products resulted in lower ammonia levels than corncob at the end of the 14-d cage-change interval. Our data indicate that pelleted or refined diced cellulose are viable alternatives to natural bedding products in IVC to limit the risk of exposure of mice to high ammonia levels.