Evaluation of different central nervous system depressors combined with ketamine for anaesthesia in mice

The aim of this study was to compare some depressors of the central nervous system combined with ketamine in order to find an adequate scombination for anaesthesia in mice, coupled with a simple, easy to use and reliable method. Forty Swiss OF-1 mice (Mus musculus), 20 females and 20 males with a body weight from 35 to 45 g aged from 12 to 16 weeks, were used to evaluate one of the following central nervous system depressors (CNSD): acepromazine (5 mg/kg), diazepam (5 mg/kg), medetomidine (1 mg/kg), midazolam (5 mg/kg) and xylazine (10 mg/kg) combined with the dissociative anaesthetic ketamine (100 mg/kg) by the intraperitoneal route. Different parameters were evaluated at regular intervals to assess the depth of anaesthesia (time of induction, time of loss and recovery of pedal withdrawal reflex, time of recovery from the anaesthesia), and respiratory and heart rate and oxygen saturation. Most of the assessment times and physiological parameters were exhibited earlier in females than in males but, in most cases, these differences were not significant. The diazepam combination resulted in death in half of the male group. Significant differences for the combination comparison were found for induction, pedal withdrawal reflex and recovery from anaesthesia, as well as for respiratory and heart rate and oxygen saturation. The best results for mice of both genders, i.e. induction, maintenance and recovery from anaesthesia were more stable with α2-agonists than with other combinations (benzodiazepines or acepromazine), which did not reach a good anaesthetic level, that is, an adequate anaesthetic plane with an absence of the pedal withdrawal reflex and the maintenance of stable vital constants.