Comparison of the effects of althesin and barbiturates on the neocortex and hippocampus in cats.

In the cat, the e.e.g. of the neocortex and the hippocampus and the cortical evoked potentials to central sensory pathway stimulation seen during Althesin anaesthesia were compared with those seen during barbiturate anaesthesia. During Althesin anaesthesia the neocortical e.e.g. displayed spindle-like activity, which was similar to that seen during barbiturate anaesthesia. Although both Althesin and pentobarbitone blocked arousal theta waves of the hippocampal e.e.g., remarkably high-amplitude spikes which were not seen during pentobarbitone anaesthesia appeared in the deep stage of Althesin anaesthesia. Althesin and barbiturates caused similar changes in the cortical evoked potentials. During light anaesthesia they showed wide variability of amplitude and in deeper anaesthesia they were markedly depressed. However, the postsynaptic components of the potentials were conversely enhanced in very deep anaesthesia when the e.e.g. was flat. Although Althesin and barbiturates cause different e.e.g. changes in the hippocampus, their depression effects on neocortical activity seem to be very similar.