Influence of local anesthetics and dissociative anesthetic ketamine on vocalization induced by electrical stimulation of sciatic nerve in rabbits

Abstract

The intravenous use of local anesthetics-particularly, lidocaine-as an analgesic, has interested anesthesiologists in recent years. They have reported the value of lidocaine as part of a mixed general anesthetic and as an analgesic for a postoperative pain. The dissociative anesthetic, ketamine, was reported to produce conspicuous analgesia. Therefore, the following experiments were performed to determine the analgesic effects of local anesthetics and ketamine on vocalization after nociceptive stimulation in the rabbit. Vocalization was produced by electrical stimmulation to the sciatic nerve in urethane light-anesthetized rabbits. To analyze the mechanism of production of vocalization, vocalization during stimulation and vocalization afterdischarge was distinguished in this study, because the former was formed through spinal internuncials and the latter through a thalamic sensory relay. Local anesthetics lidocaine, mepivacaine and procaine, when administered intravenously, inhibited vocalization. Vocalization afterdischarge was particularly inhibited more remarkably than vocalization during stimulation. Of the three local anesthetics studied, lidocaine was found to be most effective, followed by mepivacaine and procaine. The ketamine action was similar to that of local anesthetics that is the suppression of vocalization afterdischarge at low doses and both vocalization during stimulation and after discharge at high doses. The duration of action was shorter than that of local anesthetics and the recovery was very faster in comparison with local anesthetics. The studies thus suggest that in addition to the thalamus, a well-known pain receptive site, vacalization afterdischarge in the rabbit, depends upon the integrity of thalamo-neocortical circuits, and furthermore, it was discussed that catecholaminergic, dopaminergic and cholinergic neurones in the central nervous system may be play an important role in the mechanism of vocalization afterdischarge.