Towards optimized anesthesia protocols for stereotactic surgery in rats: Analgesic, stress and general health effects of injectable anesthetics. A comparison of a recommended complete reversal anesthesia with traditional chloral hydrate monoanesthesia

Brain Res. 2016 Jul 1;1642:364-375. doi: 10.1016/j.brainres.2016.04.019. Epub 2016 Apr 8.


Although injectable anesthetics are still widely used in laboratory rodents, scientific data concerning pain and distress during and after stereotactic surgery are rare. However, optimal anesthesia protocols have a high impact on the quality of the derived data. We therefore investigated the suitability of recommended injectable anesthesia with a traditionally used monoanesthesia for stereotactic surgery in view of optimization and refinement in rats. The influence of the recommended complete reversal anesthesia (MMF; 0.15mg/kg medetomidine, 2mg/kg midazolam, 0.005mg/kg fentanyl; i.m.) with or without reversal and of chloral hydrate (430mg/kg, 3.6%, i.p.) on various physiological, biochemical and behavioral parameters (before, during, after surgery) was analyzed. Isoflurane was also included in stress parameter analysis. In all groups, depth of anesthesia was sufficient for stereotactic surgery with no animal losses. MMF caused transient exophthalmos, myositis at the injection site and increased early postoperative pain scores. Reversal induced agitation, restlessness and hypothermia. Even the low concentrated chloral hydrate led to peritonitis and multifocal liver necrosis, corresponding to increased stress hormone levels and loss in body weight. Increased stress response was also exerted by isoflurane anesthesia. Pronounced systemic toxicity of chloral hydrate strongly questions its further use in rodent anesthesia. In view of undesired effects of MMF and isoflurane, thorough consideration of anesthesia protocols for particular research projects is indispensable. Reversal should be restricted to emergency situations. Our data support further refinement of the current protocols and the importance of sham operated controls.

Keywords: Chloral hydrate; Complete reversal anesthesia; Injectable anesthetic; Refinement.

Publication types

  • Comparative Study

MeSH terms

  • Anesthesia / adverse effects
  • Anesthesia / methods*
  • Anesthetics / administration & dosage
  • Anesthetics / toxicity
  • Animals
  • Chloral Hydrate / administration & dosage
  • Chloral Hydrate / toxicity
  • Female
  • Fentanyl / administration & dosage
  • Injections / adverse effects
  • Isoflurane / administration & dosage
  • Male
  • Medetomidine / administration & dosage
  • Midazolam / administration & dosage
  • Models, Animal*
  • Pain, Postoperative / pathology
  • Pain, Postoperative / physiopathology
  • Pain, Postoperative / prevention & control
  • Rats*
  • Stereotaxic Techniques*
  • Stress, Psychological / etiology
  • Stress, Psychological / pathology
  • Stress, Psychological / physiopathology
  • Stress, Psychological / prevention & control


  • Anesthetics
  • Chloral Hydrate
  • Isoflurane
  • Medetomidine
  • Midazolam
  • Fentanyl