Effect of Ketamine on the Stapedius Reflex in the Squirrel Monkey

Abstract

\s=b\We evaluated the effect of ketamine hydrochloride on the acoustically elicited stapedius reflex of squirrel monkeys. After intramuscular injection, in the presence of normal tympanometry, the amplitude of the contralateral stapedius reflex was severely depressed, even at low, preanesthetic dose levels. Possible mechanisms for the mediation of this unexpected effect are discussed. (Arch Otolaryngol 1984;110:22-24) Acoustic impedance measurement -¿A-of the middle-ear-muscle reflex has been found to be a useful tech¬ nique for the evaluation of middle-ear function1 and for the monitoring of the sensorineural hearing level2 in the squirrel monkey. While attempting to use impedance audiometry as a tech¬ nique to trace neural pathways medi¬ ating the acoustic reflex in the squir¬ rel monkey, it became apparent that although restraint of this rather active animal did allow for impedance measurement, the restraining chair itself did not completely eliminate movement artifact in some of the records. It seemed possible, however, that chemical restraint might be help¬ ful in eliminating the movement arti¬ fact.Since the use of barbiturates, eg, pentobarbital (Nembutal) sodium has been shown to depress the stapedius reflex in cat,3 rabbit," and man,5 we attempted to use an anesthetic other than a barbiturate during stapedius reflex measurements.Ketamine hydrochloride, a dissocia¬ tive anesthetic, acts on the CNS unlike that of barbiturates such as pentobar¬ bital. Whereas pentobarbital simply depresses the CNS, ketamine acts more capriciously. For example, in low doses in rat, cat, dog, tree shrew, bush baby, and squirrel monkey, ketamine acts as an analgesic rather than an anesthetic. That is, ketamine provides an insensibility to pain with¬ out loss of consciousness. In much higher doses, however, (eg, 200 to 250 mg/kg for rat and 150 to 200 mg/kg for squirrel monkey) ketamine be¬ haves as a general anesthetic with loss of consciousness and pain. But even at this level of anesthesia (which is suitable for surgical procedures) some skeletal motor tonus may remain. It is generally thought that ketamine has a depressant effect on thalamic and cortical activity, while concurrently stimulating the reticular and limbic systems.6 Of special con¬ cern to our study are reports that ketamine has little effect on the mus¬ cles of mastication,1 muscles of facial expression,8 and gag and cough reflexes.9 Additionally, while keta¬ mine also appears to decrease meta¬ bolic activity in the inferior colliculus and medial geniculate body,10 its lack of effect on the auditory brain-stem response" indicates that it must not have a substantial effect on auditory activity below the midbrain level.Thus, all evidence indicated to us that ketamine, since it does not inhib¬ it all skeletal motor systems and since it does not affect the hindbrain audi¬ tory system (through which the stape¬ dius reflex arc presumably travels), would be a suitable drug to use to restrain squirrel monkeys during sta¬ pedius reflex measurements.To determine the ...

The Middle Ear Muscle Reflex in Rat: Developing a Biomarker of Auditory Nerve Degeneration

“…Moreover Sims and Horohov reported no influence of Xylazine or Ketamine on the contralateral reflex in cat. In contrast, Thompson and colleagues (1984) indicated that the amplitude of the contralateral reflex was greatly reduced in squirrel monkey even at low doses (i.e 5 mg/kg) of Ketamine. Interestingly, our initial animal species chosen for developing and animal model of the MEM reflex was gerbil.…”

Auditory brainstem responses predict auditory nerve fiber thresholds and frequency selectivity in hearing impaired chinchillas

“…Previous studies show that ketamine depresses the middle ear reflex in squirrel monkeys (Thomson et al, 1984), which could increase the degree of hearing loss in the low to mid frequency range (e.g., ≤4 kHz; Borg et al, 1983). In contrast, isoflurane, halothane, and pentobarbital in mice appear to protect the cochlea to some extent from noise induced damage (Chung et al, 2007).…”