Effects of Volatile Anesthetics on the Evoked Potentials and Unitary Discharges in the Central Auditory System Caused by Click Stimuli in Cats

Abstract

Physiological significance of the auditory cortex in the central nervous system was firstly investigated by Kornmuller (1), Bremer and Dow (2) and using electrophysiological technique, and mapping of the primary (AI) and secondary areas (All) of auditory cortex was introduced by Ades (4), Woolsey and Walzl (6) and Rose and Woolsey (7). The inferior colliculus, the largest relay nucleus in the specific auditory pathway, receives the afferent impulses from the ipsilateral and contralateral cochlear nuclei, superior olivary nuclei and lateral lemniscus, and projects the ascending fibers to the medial geniculate body of thalamus and the auditory cortex. There are another nonspecific projection system to the auditory cortex, which passes through the midbrain reticular formation and medial ascending route (8-12). Takaori et al. (13) have shown that electrical stimulation of the various areas of midbrain reticular forma tion inhibits or facilitates the evoked click responses in the auditory cortex and medial geniculate body but it does not affect the click responses in the inferior colliculus. have demonstrated that small doses of pentobarbital sodium, chloralose and chlorpromazine facilitate the click responses in the auditory cortex of cats but urethane and ethyl alcohol depress them in proportion to the doses. These findings are noteworthy, because the sites of action of the central depressants are different each other in the auditory system which has considerably complicated fiber connection. How ever, there are not enough informations about the mode of action of volatile anesthetics on the central auditory system. The present experiments are challenge to know the effects of inhalation of volatile anesthetics such as ether, chloroform, fluothane and nitrous oxide on the evoked potentials in the auditory cortex and inferior colliculus and the uni tary discharges in the inferior colliculus caused by click stimulation in the encephale isole preparation of cats and to compare the action of the volatile anesthetics with that of bar biturate, chloralose, urethane and chlorpromazine reported previously (14-17).

Effects of Morphine on Unit Discharges Recorded From the Trigeminal Nuclei in Cats

“…The details of the experimental procedures were described elsewhere (7,8). Under ether anesthesia a tracheal cannula was inserted and the head of the animal was fixed on a stereotaxic instrument of Todai-Nohken type.…”

An Animal Model for Investigating the Clinical Utility of Somatosensory Evoked Potentials

“…8-42 Many studies using powerful anesthetics record SEPs from a highly depressed cortex. [17][18][19][20] The level of cortical depression, however, can be easily monitored by CSAs. [43][44][45][46][47] This allows an investigator to record SEPs from a highly active cortex, similar to the level of activity in most human cortical potential recordings.…”