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GENERAL ARTICLES

Inhaled Nonimmobilizers Do Not Alter the Middle Latency Auditory-Evoked Response of Rats

Department of Anesthesia and Perioperative Care, University of California, San Francisco

Address correspondence to Dr. Rampil, C-450, 521 Parnassus, San Francisco, CA 94143-0649. Address e-mail to ira_rampil{at}vaxine .ucsf.edu.

General anesthetics cause surgical immobility and oblivion (unconsciousness and amnesia). A class of compounds known as "nonimmobilizers" were predicted to be anesthetic, based on their physiochemical properties, but found to cause only amnesia. In humans, cerebrocortical electrical activity after auditory stimulation is depressed by concentrations of anesthetics which impair auditory recall. We sought to use these evoked responses to characterize the effects of the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N) and conventional inhaled anesthetics on early sensory processing in rats. Unrestrained rats with chronically implanted epidural silver screw electrodes were put into a chamber. On separate days, the same population of rats were exposed to isoflurane, desflurane, nitrous oxide, or 2N, each at several subminimum alveolar concentration of anesthetic required to eliminate movement in response to a noxious stimulus concentrations. After equilibration at each concentration, auditory-evoked responses were obtained. The behavioral state (activity and righting reflex) and electroencephalogram were also examined. 2N did not significantly change the middle latency auditory-evoked response, whereas the anesthetics all slowed conduction and depressed amplitude in a dose-dependent fashion. 2N neither depressed the righting reflex, nor induced epileptiform activity.

Implications: Although the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N) suppresses learning, we find that 2N does not depress middle latency auditory-evoked responses. This suggests that 2N may suppress learning by depressing transmission through rostral subcortical structures, such as the amygdala, rather than by acting on the brainstem or neocortical structures.

This article has been cited by other articles:

				E. I Eger II, Y. Xing, R. Pearce, S. Shafer, M. J. Laster, Y. Zhang, M. S. Fanselow, and J. M. Sonner Isoflurane Antagonizes the Capacity of Flurothyl or 1,2-Dichlorohexafluorocyclobutane to Impair Fear Conditioning to Context and Tone Anesth. Analg., April 1, 2003; 96(4): 1010 - 1018. [Abstract] [Full Text] [PDF]

				R. C. Dutton, A. J. Maurer, J. M. Sonner, M. S. Fanselow, M. J. Laster, and E. I Eger II Short-Term Memory Resists the Depressant Effect of the Nonimmobilizer 1-2-Dichlorohexafluorocyclobutane (2N) More than Long-Term Memory Anesth. Analg., March 1, 2002; 94(3): 631 - 639. [Abstract] [Full Text] [PDF]

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999