Irradiation of Rodents (IACUC)
BU IACUCInstitutional Animal Care and Use Committee IACUC oversee... approved May 2009, Revised January 2014, Reviewed July 2019, Approved September 2022
Boston University is committed to observing federal guidelines and AAALAC international guidelines for the humane care and use of animals.
Adherence to the policy is mandatory unless a specific exception has been approved by the IACUC.
Dosing and aftercare of irradiated rodents must be described in the IACUC protocol. Humane endpoints related to weight loss, body condition, or general signs of illness in mice must also be described in the protocol. Daily monitoring for the first 14 days must be performed and recorded by laboratory personnel.
Animals are recommended to be switched to chlorinated (Hydropac) or acidified water (pH 2.5-3.0) from 1 week prior to 2 weeks post irradiation. SulfaTrim antibiotic water, softened food, and/or DietGel (or similar products) may also be indicated during the first 14 days post-irradiation and should be described in the protocol if used.
Information and Guidelines
Rodents are often exposed to ionizing radiation in the fields of immunology and cancer biology. Total-body irradiation (TBI) is both cytotoxic and immunosuppressive, eliminating rapidly dividing cells and impairing the immune system from rejecting foreign donor cells being transplanted. Irradiation is frequently used to produce myeloablation preparatory to bone marrow transplantation (BMT).
Animals to be lethally irradiated should be healthy and free from infectious agents. Immunocompetent mice are not as susceptible to illness from commensal microbial agents they may carry. After exposure to total whole-body irradiation (TBI), rodents are immunocompromised and subject to infections not previously clinically significant. If post-irradiation infections occur and interfere with recovery of the animals, this possibility should be taken into consideration during study planning.
Animals are recommended to be placed in pie cages for irradiation to limit mobility and ensure equal doses of irradiation. Anesthesia is optional for irradiation. Animals are generally irradiated for a short period of time (<15 minutes). The amount of time spent inside the irradiator varies depending upon the dose and the radioisotope decay charts.
Irradiation procedures must be scheduled via the Radiation Protection office. If the dose is to be fractionated, this also must be specified and scheduled.
Post-procedure, daily monitoring for the first 14 days should be performed and recorded by laboratory personnel. Care, especially during the first week, should be dedicated to keeping animals as comfortable as possible, ensuring hydration, and providing access to moistened food and/or nutritional diet gel. Irradiated mice may lose up to 25% of their body weight with radiation sickness, which in the case of a successful bone marrow transplant will be mostly regained by day 14-21 post-irradiation.
It is important to realize that even after bone marrow transplantation, lethally irradiated mice are severely immunosuppressed for the first two weeks and providing a sterile housing environment is recommended.5 Sterile caging, food, and water is strongly recommended and is required if post-irradiation complications occur.
Humane Endpoints for Irradiated Mice
In the case of bone marrow replacement, transplanted animals undergo a 5–10 day irradiation sickness period from which they generally recover within 14 days.5 Clinical signs of morbidity should be closely monitored, and veterinary staff should be consulted if animals are not improving within 14 days. If not recovered after 21 days, euthanasia should be considered.
Gamma irradiation: one type of ionizing irradiation. The source may be 137cesium, 60cobalt, or high-energy X-rays.
Gray (Gy): the SI unit of absorbed radiation dose due to ionizing radiation.
Rad: a largely obsolete unit of absorbed radiation dose. It is now superseded in the SI by the “gray”. 100 rads = 1 gray (Gy).
Fractionation of dose: The total irradiation dose is split into two or more equal parts separated by a time interval to minimize morbidity and mortality.
Doses of Radiation
There are numerous literature references reporting differences in sensitivity in radioresistance or radio susceptibility to radiation damage in different strains of mice. Appropriate radiation dosage is key to successful irradiation. Inappropriate dosing may lead to increased morbidity with excessive doses or decreased experimental success with insufficient doses. If the PI is unfamiliar with the strain to be used or the radiation source, it is advisable to irradiate a small number of animals in a pilot study to determine the optimal dose for the project and strain under study. Mice of the C57BL strain are more resistant to irradiation damage, whereas BALB/c mice are more sensitive. The age of the mouse is important as well, with older mice being more resistant. For myeloablation in preparation for BMT, total whole-body irradiation (TBI) is used. Doses of 700 to 1300 cGy are myeloablative.5
- Boston University IACUC Policy for Humane Endpoints.
- Cooligan, J.E et al. 2006. Current protocols in immunology. In Current protocols, R. Coico, ed., pp.1.1.1-1.11.4. John Wiley & Sons Inc., Hoboken.
- Crawford, PA and Gordon, JI Microbial regulation of intestinal radiosensitivity. PNAS 102(37); Sept. 13, 2005.
- Duran-Struuck, R. et.al. 2008. Differential susceptibility of C57BL/6NCr and B6.Cg-Ptprca mice to commensal bacteria after whole-body irradiation in translational bone marrow transplantation studies. J Transl Med: 6:10.
- Duran-Struuck, R. and Dysko, R. Principles of Bone Marrow Transplantation (BMT): Providing Optimal Veterinary and Husbandry Care to Irradiated Mice in BMT Studies. JAALAS 48(1): 2009. 11–22.
- Hanson et. al. 1987. Comparison of intestine and bone marrow radio sensitivity of the BALB/c and the C57BL/6 mouse strains and their B6CF1 offspring. Radiat Res 110:340–352.
- Iwakawa, M. et. al. 2003. Different radiation susceptibility among five strains of mice detected by skin reaction. J Radiat Res (Tokyo) 44: 7–13.
- Kassayova, E. et.al. 1999. Two-Phase Response of Rat Pineal melatonin to Lethal Whole-Body Irradiation with Gamma Rays. Physiol. Res. 48:227–230.
- The Guide for the Care and Use of Laboratory Animals. NRC. ILAR. 2011. P.12.
- The Mouse in Biomedical Research. Vol 3. Fox J.G et. Al. Eds. 2nd Ed. 2007. Academic Press. ACLAM Series. Pp. 453–454.