Evaluation of cage micro-environment of mice housed on various types of bedding materials.

A variety of environmental factors can affect the outcomes of studies using laboratory rodents. One such factor is bedding. Several new bedding materials and processing methods have been introduced to the market in recent years, but there are few reports of their performance. In the studies reported here, we have assessed the cage micro-environment (in-cage ammonia levels, temperature, and humidity) of mice housed on various kinds of bedding and their combinations. We also compared results for bedding supplied as Nestpaks versus loose bedding. We studied C57BL/6J mice (commonly used) and NOD/LtJ mice (heavy soilers) that were maintained, except in one study, in static duplex cages. In general, we observed little effect of bedding type on in-cage temperature or humidity; however, there was considerable variation in ammonia concentrations. The lowest ammonia concentrations occurred in cages housing mice on hardwood bedding or a mixture of corncob and alpha cellulose. In one experiment comparing the micro-environments of NOD/LtJ male mice housed on woodpulp fiber bedding in static versus ventilated caging, we showed a statistically significant decrease in ammonia concentrations in ventilated cages. Therefore, our data show that bedding type affects the micro-environment in static cages and that effects may differ for ventilated cages, which are being used in vivaria with increasing frequency.

New mouse model to study islet transplantation in insulin-dependent diabetes mellitus.

BACKGROUND: Islet transplantation studies with diabetic rodents frequently use treatment with diabetogens such as alloxan or streptozotocin to render hosts hyperglycemic. These chemicals produce unwanted toxic side effects, which complicate interpretations of damage produced by hyperglycemia versus direct toxin-induced damage. A mouse that spontaneously developed insulin-sensitive diabetes without beta-cell autoimmunity would provide an excellent vehicle for testing beta-cell replacement protocols. The Ins2Akita mutation disrupts normal insulin processing and causes a failure in secretion of mature insulins, which results in the early development of hyperglycemia. This report examines the insulin sensitivity of mice that carry Ins2Akita and their responsiveness to engraftment with syngeneic pancreatic islets. METHODS: Ten-week-old C57BL/6J-Ins2Akita/+ males were given 1 unit of insulin to determine insulin sensitivity. Also, 10-week-old, hyperglycemic B6-Ins2Akita/+ received either 400 islets isolated from syngeneic C57BL/6J males (n=7) or from allogeneic BALB/cJ males (n=5) under the renal capsule. These mice were followed for 8 weeks after engraftment or until remission of euglycemia. Nephrectomy of the graft-containing kidney was performed on mice that remained euglycemic. These mice were then followed for 2 weeks for return of hyperglycemia. RESULTS: B6-Ins2Akita/+ mice are insulin responsive. Insulin treatment of hyperglycemic B6-Ins2Akita/+ males significantly lowered blood glucose values within 1 hr. In addition, B6-Ins2Akita/+ recipients of syngeneic islet grafts reversed their diabetic state in less than 72 hr. These islet-engrafted mice remained normoglycemic until removal of the graft-containing kidney. Removal of the graft resulted in a return to hyperglycemia. Mice that received allogeneic grafts efficiently rejected the graft. CONCLUSIONS: Our data support the hypothesis that B6-Ins2Akita/+ mice are insulin sensitive and provide an excellent model for islet transplantation studies. In addition, the reduced beta-cell mass and the absence of beta-cell autoimmunity, coupled to the fact that these mice also reject allografts, suggest that these mice may be useful for a variety of other applications, including testing functionality of human islets prepared for transplantation and perhaps also for exploring beta-cell restorative therapy using pancreatic islet stem cells.