Effects of Central Depressants on the Cortical Auditory Responses Evoked by Repetitive Click Stimuli in the Cat

Abstract

The effects of central depressants on the evoked potential and ensued rhythmic after-discharges in the auditory cortex by a series of single click stimuli in cats were previously reported (1). In contrast to a progressive depression of the evoked potential by urethane and ethyl alcohol, the intravenous infusion of pentobarbital sodium, chlo ralose and chlorpromazine produced considerable increase in amplitude of the evoked potential followed by progressive decrease. The rhythmic after-discharges became to respond regularly and uniformly to the stimulation in small doses of the central depress ants, and the duration of the discharges was prolonged with increase in the dose. It is well-known that the acoustic impulses ascend to the middle ectosylvian

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

“…Brazier (23,24) has shown that the evoked potentials in the visual cortex and Nucleus centre median of thalamus to flash stimulation are inhibited by ether but not by pentobarbital or chloralose. Table 2 summarizes the effects of ether, chloroform, fluothane and nitrous oxide on the cortical and collicular evoked click potentials and unitary discharges in the present experiments comparing with those of pentobarbital sodium, urethane and chlorpromazine reported previously (14)(15)(16)(17). The evoked click potentials in the auditory cortex and in ferior colliculus were depressed by ether inhalation almost uniformly.…”

“…The facilitator), effects of small doses of pentobarbital sodium , chloralose and chlorpro mazine on the cortical evoked click potentials have been reported by Nakai et al (14)(15)(16) in cats. These effects were observed in the supra-thalamic level, and the evoked click potentials in the inferior colliculus were not augmented by these central depressants.…”

“…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)(15)(16)(17).…”

“…The animal was kept in the sound-proof room maintained at 28°C. Details of the experimental pro cedures were followed the descriptions by Nakai et al (14)(15)(16)(17). Surgical procedures: Under ether anesthesia, the cat was inserted with tracheal cannula and the head was fixed on the stereotaxic instrument of Todai-Noken type.…”

“…Nakai et al (14)(15)(16) 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.…”