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In rats, surgically anaesthetized with Urethane, an increase in the depth of anaesthesia upon administration of ethyl carbamate (Urethane), pentobarbitone sodium (Nembutal), thiopentone sodium (Intraval), althesin, ketamine, trichloroethylene, halothane, methoxyflurane, diethyl ether, ethyl-vinyl ether, cyclopropane, enflurane or chloroform resulted in a dose-dependent increase in the latency, the decrease in the amplitudes of the initial positive and negative components of the short latency cortical response to electrical stimuli applied to the forepaw. 2. The same changes were seen when starting from initially unanaesthetized rats and anaesthetizing them with Urethane. 3. With all the inhalational agents used these changes lasted for as long as the administration except with nitrous oxide where the changes in the cortical response were transient. 4. The tranquilizing agents diazepam, chlordiazepoxide, and haloperidol showed no such action. Chloral hydrate and chlorpromazine, on the other hand, produced moderate changes in the evoked cortical response similar to those seen with the other anaesthetic agents used.
Angel et al. (1982) studied this question.