Effects of Multimodal Analgesia on the Success of Mouse Embryo Transfer Surgery

Multimodal analgesia is promoted as the best practice pain management for invasive animal research procedures. Universal acceptance and incorporation of multimodal analgesia requires assessing potential effects on study outcome. The focus of this study was to assess effects on embryo survival after multimodal analgesia comprising an opioid and nonsteroidal antiinflammatory drug (NSAID) compared with opioid-only analgesia during embryo transfer procedures in transgenic mouse production. Mice were assigned to receive either carprofen (5 mg/kg) with buprenorphine (0.1 mg/kg; CB) or vehicle with buprenorphine (0.1 mg/kg; VB) in a prospective, double-blinded placebo controlled clinical trial. Data were analyzed in surgical sets of 1 to 3 female mice receiving embryos chimeric for a shared targeted embryonic stem-cell clone and host blastocyst cells. A total of 99 surgical sets were analyzed, comprising 199 Crl:CD1 female mice and their 996 offspring. Neither yield (pups weaned per embryo implanted in the surgical set) nor birth rate (average number of pups weaned per dam in the set) differed significantly between the CB and VB conditions. Multimodal opioid–NSAID analgesia appears to have no significant positive or negative effect on the success of producing novel lines of transgenic mice by blastocyst transfer.Abbreviation: CB, carprofen–buprenorphine; ES cell, embryonic stem cell; ET, embryo transfer; NSAID, nonsteroidal antiinflammatory drug; VB, vehicle–buprenorphineSurgical transfer of mouse embryos (embryonic transfer, ET) to surrogate dams is currently standard procedure in producing transgenic mouse models for research; the technique also is used to reestablish pathogen-free stocks of mice.²⁵ The procedure is invasive, in that it penetrates the peritoneal cavity and reproductive tract, often requires bilateral flank incisions through skin and muscle (each equivalent in length to approximately 10% of the snout–anus length), entails externalization and traction of internal organs, and requires wound closure. The ideal analgesia regimen for rodent ET would safely manage pain in the recipient female mouse without adversely affecting the quality or number of offspring from implanted embryos. Studies to date have found no effect of either the opioid buprenorphine or the nonsteroidal antiinflammatory drug (NSAID) flunixin on the number of embryos surviving after ET when compared with those after untreated or saline-placebo mice.^17,20 Furthermore, no study to date has looked at whether a multimodal combination of opioid and NSAID might either improve or decrease embryo survival.In the present study, we sought to compare reproductive outcomes of NSAID–opioid analgesia compared with opioid alone in embryo-transfer recipient mice by comparing outcomes from surrogate dams treated with carprofen and buprenorphine (CB) with those from dams treated with vehicle and buprenorphine (VB). We performed our analgesic comparison in the context of ongoing work in the University of California–San Francisco Transgenics Core. The Core receives targeted embryonic stem (ES) cell clones from laboratories and microinjects them into 8-cell embryos obtained from superovulated B6D2F1/Crl and Swiss Webster mice. The Core then surgically places these embryos into 1 to 3 recipient female mice, resulting in the generation of mice chimeric for the targeted ES cells and host blastocyst cells. To minimize any effects of learning curves, disruption of routine, and variability to ongoing research, the surgeon was instructed not to deviate from Core protocol in regard to animal anesthesia, handling, or housing. Therefore, the only change was to substitute buprenorphine with either carprofen–buprenorphine or vehicle–buprenorphine.Measured outcomes were the average number of weaned offspring produced per embryo implanted in the surgical set (that is, yield) and the average number of weaned offspring produced per dam in the surgical set (that is, birth rate).