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Repeated Administration of Tribromoethanol in C57BL/6Nhsd Mice

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Repeated Administration of Tribromoethanol in C57BL/6Nhsd Mice Journal of the American Association for Laboratory Animal Science Vol 52, No 2 Copyright 2013 March 2013 by the American Association for Laboratory Animal Science Pages 176–179 Repeated Administration of Tribromoethanol in C57BL/6NHsd Mice William A Hill,1,3,* Jacquelyn T Tubbs,5 Christopher L Carter,3 Jane A Czarra,3 Kimberly M Newkirk,1 Tim E Sparer,4 Barton Rohrbach,1 and Christine M Egger2 We evaluated the effect of repeated intraperitoneal administration of tribromoethanol on various parameters in C57BL/6NHsd mice. Mice (n = 68) were randomly assigned to 1 of 7 groups to receive tribromoethanol (500 mg/kg IP) on day 0 or days 0 and 8; vehicle (tert-amyl alcohol in sterile water) only on day 0 or days 0 and 8; sterile water injection on day 0 or days 0 and 8; or no treatment. A single dose of tribromoethanol failed to produce loss of pedal reflex and had no effect on median food and water consumption but altered median body weight on days 1 through 4 when compared with that in mice that received vehicle only or no treatment. Median body weight did not differ between mice that received a single dose of tribromoetha- nol and those that received an injection of water. Among mice given 2 doses of tribromoethanol, induction time, anesthetic duration, and recovery time varied widely. Repeated administration of tribromoethanol had no effect on median food and water consumption or body weight compared with those in controls. Median liver weight was significantly greater in mice that received 2 doses compared with a single dose of tribromoethanol. Median liver weight did not differ between untreated mice and those that received tribromoethanol. No significant organ or tissue pathology was observed in any study animal. Although tribromoethanol did not produce morbidity, mortality, or pathologic changes in treated animals, we urge caution in use of tribromoethanol in C57BL/6NHsd mice due to its variable anesthetic effectiveness. Tribromoethanol, a nonpharmaceutical-grade anesthetic, Materials and Methods has been used extensively for various manipulations in labo- Animals. Female C57BL/6NHsd mice (n = 68; age, 38 to 45 d) ratory rodents due to its ready availability, lack of state and were obtained from Harlan Laboratories (Haslett, MI). Mice federal drug regulations associated with its use, and rapid were singly housed in static, polysulfone, microisolation caging 10 anesthetic induction and recovery times. Tribromoethanol is on corncob and cellulose bedding (Harlan Teklad, Madison, commercially available as a white crystalline powder that, when WI) and maintained on a 12:12-h light:dark cycle. Mice were reconstituted and administered, produces generalized CNS provided tap water and standard, pelleted, rodent chow depression, including depression of respiratory and cardio- (Harlan Teklad) ad libitum. Caging, food, and water bottles were 11 vascular centers. Despite routine use, tribromoethanol use changed weekly by using aseptic technique within a laminar in rodents remains controversial due to contradictory reports flow transfer station (Nuaire, Plymouth, MN). Mice were used regarding the compound’s efficacy and associated pathology pursuant to an IACUC-approved protocol and were housed 8,13,14,15,16,20 and mortality. Morbidities reported with tribro- and cared for in compliance with the Guide for the Care and Use moethanol use in mice include intestinal ileus, peritonitis, of Laboratory Animals6 in an AAALAC-accredited program. 8,16,20 muscle necrosis, serositis of abdominal organs, and death. Group allocation. Mice were acclimated for 5 d prior to In an attempt to balance animal welfare concerns and inves- experimental use. After acclimation, mice were randomly as- tigator needs, many IACUC have developed guidelines for signed to 1 of 7 groups to receive tribromoethanol (500 mg/kg IP) tribromoethanol use, including prohibiting its repeated use in on day 0 or days 0 and 8; vehicle (tert-amyl alcohol in sterile individual animals. A single study published in 1979 described water) intraperitoneally on day 0 or days 0 and 8; sterile water 5 high mortality after repeated tribromoethanol injection, and intraperitoneally on day 0 or days 0 and 8; or no treatment. All although no experimental details were provided, the report groups contained 10 mice each, except for the no-treatment likely has influenced institutional policies. group (n = 8). In the current study, we determined the effect of repeated Tribromoethanol. The tribromoethanol dose (500 mg/kg IP) tribromoethanol administration on induction time, anesthetic used in this study followed the preparation and dosing recom- duration, recovery time, food and water consumption, body mendations outlined by our IACUC.19 Briefly, a 1.61-g/mL weight, morbidity, mortality, and pathology in C57BL/6NHsd stock solution was prepared by adding 6.2 mL tert-amyl alcohol mice. To our knowledge, this study is the first to thoroughly (Sigma–Aldrich, St Louis, MO) to 10 g 2,2,2-tribromoethanol evaluate the safety and efficacy of repeated tribromoethanol (99%; lot number A0278709, Acros Organics, Geel, Belgium). A administration. 25-mg/mL working solution was prepared by adding 0.78 mL of the tribromoethanol stock solution to 49.2 mL tissue-grade Received: 22 Jun 2012. Revision requested: 30 Jul 2012. Accepted: 05 Sep 2012. double-distilled H20 (Fisher Scientific, Pittsburgh, PA); the Departments of 1Biomedical and Diagnostic Sciences and 2Small Animal Clinical Sciences, working solution was filtered through a 0.2-mm syringe filter Institute of Agriculture, Knoxville, 3Office of Laboratory Animal Care, and4 Department (Fisher Scientific) prior to injection in mice. The stock solution of Microbiology, University of Tennessee, Knoxville, Tennessee; 5Laboratory Animal Resources, Duke University, Durham, North Carolina. was made 1 d prior to injection and allowed to stir overnight at *Corresponding author. Email: [email protected] room temperature; the working solution was made immediately 176 Tribromoethanol anesthesia of mice prior to injection. The pH of the working solution was not de- termined. Tribromoethanol powder from the same bottle and lot number was used throughout this study. The vehicle-only solution contained the same ratio of tert-amyl alcohol and sterile water as that in the tribromoethanol working solution. Tribromoethanol efficacy and safety. Intraperitoneal injections were performed according to group allocation and current body weight and by a single investigator (JT). All mice (except the untreated group) received injection volumes of 0.31 to 0.44 mL. After tribromoethanol injection, mice were maintained on a circulating-water heating pad (Gaymar Industries, Orchard Park, NY) and monitored for anesthetic induction time, du- ration of anesthesia, and recovery time. Induction time was defined as the time from tribromoethanol administration to loss of the pedal reflex. Anesthetic duration was defined as the time between the loss and return of pedal reflex. Recovery time was defined as the time between return of the pedal reflex to movement around the primary enclosure. According to a Figure 1. Equipment used to evaluate the pedal reflex after tribro- 8 previously described procedure, we assessed the pedal reflex moethanol administration. by using a Touch-Test Sensory Evaluator (North Coast Medi- cal, Gilroy, CA) with a target force of 300 g (Figure 1); a single from the model, data were rank-transformed. The procedure of investigator (CC) performed all assessments. Presence of the Bonferroni was used to adjust for multiple comparisons among pedal reflex was defined as withdrawal of the limb on contact treatment groups. Induction time, anesthetic duration, and by the sensory evaluator. Body weight and food and water recovery time were summarized for group 2 using the median intake were measured daily by using a digital laboratory scale and range. Data, whether transformation was necessary for the (Denver Instrument, Arvada, CO). Daily intake was quantified purposes of statistical analysis, are presented as raw means and by determining the remaining mass of offered food and water. range for each treatment group over the stated time period, for Pathologic evaluation. Mice that received injections only on the purpose of consistency. A P value of less than or equal to 0.05 day 0 were euthanized on day 4; those injected on days 0 and was used to determine statistical significance in all tests. 8 were euthanized on day 11. Untreated mice were euthanized on day 4 (n = 3) or 11 (n = 5). All mice were euthanized via cer- Results vical dislocation under CO2 anesthesia. After euthanasia, each mouse was necropsied, and gastrointestinal tract, spleen, and All mice (n = 20) that received tribromoethanol became liver were harvested and immediately weighed. The stomach, recumbent yet retained pedal reflex after a single dose of tri- small intestine, cecum, colon, liver, spleen, and a sample of bromoethanol administration; 9 of the 10 mice that received the body wall were collected for histopathologic evaluation. a second dose 8 d after the first lost the pedal reflex after the Tissues were fixed in 10% formalin, stained with hematoxylin repeated administration. In these 9 mice, induction time ranged and eosin, and evaluated by a single veterinary pathologist from 2.0 to 7.0 min (median, 3.0 min), anesthetic duration (KN) blinded to treatment group. By using a previously pub- ranged from 5.0 to 16.0 min (median, 12.0 min), and recovery lished algorithm for evaluation of tribromoethanol-induced time ranged from 17.0 to 32.0 min (median, 26.00 min; Figure 2). changes,8 histopathologic lesions were scored on a scale of Tribromoethanol administration decreased (P < 0.05) median 0 to 4 reflecting the severity of inflammation and percentage body weight on days 1 through 4 when compared with that of of organ affected. mice that received vehicle or no treatment but not sterile water Statistical analysis. All statistical analyses were performed by (Table 1). Values for food consumption, water consumption, using SAS version 9.2 (SAS Institute, Cary, NC).
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