Surgical procedures in neonatal rats

The explicit goal is to minimize procedural differences between young and adult animals (see Simons and Carvell, 1989) Anesthesia was induced with isoflurane and maintained with halothane in 50/50 N2/O2 mixture. For P13-15 and P20-22 pups, initial halothane concentration was 2% which was then reduced to 1.5% after approximately 3 minutes to avoid respiratory depression. For P27-29 and P65 animals, initial halothane concentration was 2.5% reduced to 1.8% after 3-5 minutes. Depth of anesthesia during surgery was monitored using respiratory rate and absence of foot or tail withdrawal in response to pinch. In P13-15 and P20-22 pups, respiratory rate of approximately 60 breaths per minute was found to correspond to adequate anesthetic control with minimal risk of lethal overdose. Hypothermia, especially in younger animals, was prevented by warming the rats with a 20W halogen lamp. In our experience, the lamp should be positioned no closer than 8 inches from the body to avoid halothane-related malignant hyperthermia.