An optimized mouse parabiosis protocol for investigation of aging and rejuvenative mechanisms.

Surgical parabiosis enables sharing of the circulating milieu between two organisms. This powerful model presents diverse complications based on age, strain, sex, and other experimental parameters. Here, we provide an optimized parabiosis protocol for the surgical union of two mice internally at the elbow and knee joints with continuous external joining of the skin. This protocol incorporates guidance and solutions to complications that can occur, particularly in aging studies, including non-cohesive pairing, variable anesthesia sensitivity, external and internal dehiscence, dehydration, and weight loss. We also offer a straightforward method for validating postoperative blood chimerism and confirming its time course using flow cytometry. Utilization of our optimized protocol can facilitate reproducible parabiosis experimentation to dynamically explore mechanisms of aging and rejuvenation.

Behavioral and Physiologic Effects of Dirty Bedding Exposure in Female ICR Mice.

Exposure of sentinel mice to dirty bedding is commonly used in health monitoring programs to screen colonies for clinical and subclinical disease. Despite the potential stressors present in dirty bedding, including but not limited to microorganisms, pheromones, and ammonia, it is unknown whether sentinel mice exposed to soiled bedding experience stress. In this study, select behavioral and physiologic changes associated with stress were assessed in female ICR mice exposed to dirty bedding. Behavioral parameters included evaluation in the home cage and selected behavioral tests; physiologic measurements included neutrophil:lymphocyte ratio and weight. Mice in the acute group were exposed for 24 h whereas mice in the chronic group were exposed for 4 wk. Mice in the chronic group exposed to dirty bedding weighed less at days 21 and 28 than did control mice. Chronic mice exposed to dirty bedding also exhibited decreased net weight gain over the entire study period as compared with control mice. No significant differences were detected in the other behavioral and physiologic parameters measured. These results indicate that dirty bedding exposure may affect sentinel mice, but further investigation is needed to determine the specific mechanism(s) behind the weight difference.

Indicators of Postoperative Pain in Syrian Hamsters (Mesocricetus auratus).

Despite the use of Syrian hamsters (Mesocricetus auratus) in research, little is known about the evaluation of pain in this species. This study investigated whether the frequency of certain behaviors, a grimace scale, the treat-take-test proxy indicator, body weight, water consumption, and coat appearance could be monitored as signs of postoperative pain in hamsters in a research setting. Animals underwent no manipulation, anesthesia only or laparotomy under anesthesia. An ethogram was constructed and used to determine the frequencies of pain, active and passive behaviors by in-person and remote videorecording observation methods. The Syrian Hamster Grimace Scale (SHGS) was developed for evaluation of facial expressions before and after the surgery. The treat-take-test assessed whether surgery would affect the animals' motivation to take a high-value food item from a handler. The hypothesis was that behavior frequency, grimace scale, treat-take-test score, body weight, water consumption, and coat appearance would change from baseline in the surgery group but not in the no-intervention and anesthesia-only groups. At several time points, pain and passive behaviors were higher than during baseline in the surgery group but not the anesthesia-only and no-intervention groups. The SHGS score increased from baseline scores in 3 of the 9 animals studied after surgery. The frequency of pain behaviors and SHGS scores were highly specific but poorly sensitive tools to identify animals with pain. Behaviors in the pain category were exhibited by chiefly, but not solely, animals that underwent the laparotomy. Also, many animals that underwent laparotomy did not show behaviors in the pain category. Treat-take-test scores, body weight, water consumption, and coat appearance did not change from baseline in any of the 3 groups. Overall, the methods we tested for identifying Syrian hamsters experiencing postoperative pain were not effective. More research is needed regarding clinically relevant strategies to assess pain in Syrian hamsters.

Use of a Rat Model to Study Ventral Abdominal Hernia Repair.

Ventral abdominal hernia is a relatively common clinical condition that sometimes requires herniorraphy (surgical repair). The repair of ventral abdominal hernia typically requires implantation of a material to serve as a mechanical bridge across the defect in the abdominal wall. Biomaterials, such as porcine small intestinal submucosa (SIS), also serve as a lattice for cell growth into the implant and can naturally incorporate into the host tissue. Development of such repair materials benefits from use of animal models in which experimental abdominal wall defects are easily created and are amenable to repair in a reproducible fashion. The method offered here describes surgical creation and repair of ventral abdominal hernia in a rat model. When SIS is used to repair an experimental ventral abdominal hernia in this model, it is rapidly incorporated into host tissue within 28 days of implantation. Histologically, incorporation of their implanted material into host tissue is characterized by a robust fibrovascular response. Future refinements and applications of the rat abdominal hernia model may likely involve diabetic and/or obese animals as a means to more closely mimic common co-morbidities of man.