Preliminary studies have suggested a correlation between postsurgical pain and nest building behaviour in laboratory mice. However, there is no standardized measure for estimating pain by means of nest building performance. Here, we investigated nest building under various conditions, and scored nest complexity to assess postsurgical pain. Mice of both sexes, different strains [C57BL/6J, DBA/2J, and B6D2-Tg(Pr-mSMalphaActin)V5rCLR-25], and kept under different housing conditions, showed no differences in their latency to use the offered nest material. Healthy female C57BL/6J mice were engaged 4.3% of the day with nest building and showed three peaks of this behaviour: in the beginning and middle of the light phase, and in the second half of the dark phase. For assessment of postsurgical pain, female C57BL/6J mice underwent a sham embryo transfer +/− different doses of the analgesic carprofen or control treatment. Nest complexity scoring at 9 h after the experimental treatments (i.e. at the end of the light phase) resulted in less than 10% of animals with noticeably manipulated nest material (nestlet) after surgery and more than 75% of healthy mice having built identifiable-to-complex nests or had noticeably manipulated nestlets, while animals after anaesthesia-only showed intermediate nest complexity. Carprofen analgesia resulted in no (5 mg/kg) or only slight (50 mg/kg) improvement of nest complexity after surgery. Thus, nest complexity scoring can be incorporated into daily laboratory routine and can be used in mice as a sensitive tool for detecting reduced wellbeing and general condition, but probably not for determining the efficacy of pain treatment.

Detection of persistent pain of a mild-to-moderate degree in laboratory mice is difficult because mice do not show unambiguous symptoms of pain or suffering using standard methods of short-term observational or clinical monitoring. This study investigated the potential use of burrowing performance – a spontaneous and highly motivated behavior – as a measure of post-operative pain in laboratory mice. The influence of minor surgery on burrowing was investigated in adult C57BL/6J mice of both genders in a modified rodent burrowing test (displacement of food pellets from a pellet-filled tube) within the animal’s home cage. Almost all (98%) healthy mice burrowed (mean latency 1.3 h, SEM 0.5 h). After surgery without pain treatment, latency of burrowing was significantly prolonged (mean Δ latency 10 h). Analgesic treatment using the anti-inflammatory drug carprofen (5 mg/kg bodyweight) decreased latency of burrowing after surgery (mean Δ latency 5.5 h) to the level found in mice that had been anesthetized (mean Δ latency 5.4 h) or had received anesthesia and analgesia (mean Δ latency 4.6 h). Analgesia during surgery was associated with a significantly earlier onset of burrowing compared to surgery without pain treatment. A distinct gradation in burrowing performance was found ranging from the undisturbed pre-operative status to the intermediate level following anesthesia/analgesia and surgery with analgesia, to the pronounced prolongation of latency to burrow after surgery without pain relief. In conclusion, post-surgical impairment of general condition, probably mainly attributable to pain, can be conveniently assessed in laboratory mice on the basis of the burrowing test.

Isoflurane is currently the most common volatile anaesthetic used in laboratory mice, whereas in human medicine the more modern sevoflurane is often used for inhalation anaesthesia. This study aimed to characterize and compare the clinical properties of both anaesthetics for inhalation anaesthesia in mice. In an approach mirroring routine laboratory conditions (spontaneous breathing, gas supply via nose mask, preventing hypothermia by a warming mat) a 50 min anaesthesia was performed. Anaesthetics were administered in oxygen as carrier gas at standardized dosages of 1.5 minimum alveolar concentrations, which was 2.8% for isoflurane and 4.9% for sevoflurane. Both induction and recovery from anaesthesia proceeded quickly, within 1–2 min. During anaesthesia, all reflex testing was negative and no serious impairment of vital functions was found; all animals survived. The most prominent side-effect during anaesthesia was respiratory depression with hypercapnia, acidosis and a marked decrease in respiration rate. Under anaesthesia, heart rate and core body temperature remained within the normal range, but were significantly increased for 12 h after anaesthesia. Locomotor activity, daily food and water consumption and body weight progression showed no abnormalities after anaesthesia. No significant difference was found between the two anaesthetics. In conclusion, isoflurane and sevoflurane provided an equally reliable anaesthesia in laboratory mice.

Sustained-release formulations of analgesic drugs are promising alternatives to repeated drug injections. Here, we compared a sustained-release formulation of buprenorphine (SB, 2.2 mg/kg) with a standard protocol of three injections of buprenorphine (Temgesic, 0.1 mg/kg/8 h) in mice. Buprenorphine serum concentration and analgesic action (thermal sensitivity) were determined in healthy mice. Additionally, the pain relief properties of both protocols were assessed after laparotomy using physiological and ethological measures of pain and recovery. Serum concentrations and thermal sensitivity tests indicated duration of action of at least 4 h (but less than 8 h) with the Temgesic protocol, and 24–48 h with SB. Behavioural and clinical parameters indicated at least partial pain relief after surgery for both protocols. Observed side-effects of buprenorphine independent of the protocol were increased activity, disturbed circadian rhythm and several abnormal behaviours. A tendency for decreased food and water intake as well as body weight reduction was also seen. Body weight decreased significantly in animals that received three injections of Temgesic, regardless of whether surgery was performed or not (P = 0.015; P = 0.023), hinting at a stress response towards this repeated intervention. In conclusion, an application interval of 8 h (Temgesic) appears too long and might lead to repeated periods with insufficient analgesia in animals undergoing lasting and/or substantial pain after surgery. In comparison to the standard protocol, SB provided a long-lasting, assured analgesia without possible stressful repeated injections in a standard surgical model, with only limited and acceptable behavioural side-effects.