dine or bupivacaine to primates may influence behavioral maturation (Golub, 1996). In higher mammals, such as nonhuman primates, appropriate postoperative analgesia for the dam is an important precaution in preventing premature labor after intrauterine surgery (Tame et al., 1999).
For experimental protocols that require the manipulation of late-term rodent fetuses after their removal from nonanesthetized mothers (such as a dam euthanized by decapitation or cervical dislocation), guidelines for anesthesia and analgesia in neonates should be followed.
Potentially painful experimental manipulations in neonatal rodents require the use of anesthesia or analgesia unless the IACUC has approved withholding anesthesia or analgesia for scientific reasons. The primary difficulty in using anesthesia or analgesia in the neonate is balancing its effectiveness and safety. Many anesthetics that can be used safely and effectively in adult rodents are not good choices for neonates; two examples are pentobarbital and ketamine, both of which tend to be ineffective at lower doses and fatal at higher doses (Danneman and Mandrell, 1997). In general, neonatal rodents are more sensitive to anesthetic and analgesic drugs than are adult animals, and such toxic effects as respiratory and cardiac depression are more serious problems in the youngest animals (e.g., Colman and Miller, 2001; Fortier et al., 2001; Greer et al., 1995; Prakash et al., 2002).
Most of the anesthetic agents used in juvenile and adult animals are safe and effective in larger neonatal mammals (Grandy and Dunlop, 1991; Thurmon et al., 1996). The choice of anesthetic agent used may depend on species, type and duration of procedure, and availability of specialized equipment needed (such as a gas anesthesia machine with a precision vaporizer). Most anesthetic regimens used in precocious and nonrodent neonatal mammals are standard veterinary procedures.
The choice of anesthetic method or agent should be based on the procedure, expertise of the researcher, the potential for hemorrhage, and the stability of the anesthetic plane. Overall, the best results of anesthesia in neonatal rodents have been achieved with inhalant anesthetics and hypothermia. Inhalants are a reasonable first choice for anesthesia of neonatal rodents. When inhalants cannot be used—for safety or practical reasons—hypothermia should be considered as a safe and effective alternative to injectable drugs. Hypothermia has been proved safe and effective as the sole method of anesthesia for altricial rodents (such as rats and mice) up to about the age of 7 days (Danneman and Mandrell, 1997; Phifer and Terry, 1986). However, it has the potential to be noxious, and rapid cooling of nonprotected flesh is painful (Wolf and Hardy, 1941). Rat pups recovering from hypothermia—but not pups recovering from general anesthesia—emit ultrasonic vocalizations even when placed with their mothers during the recovery