Potentiation of inhibition by general anaesthetics in neurones of the olfactory cortex in vitro.

Pentobarbitone, phenobarbitone, methohexitone, chloralose and alphaxalone produced 10-fold increases in the duration of an inhibitory post-synaptic conductance (i.p.s.c.) as recorded intracellularly from neurones of the guinea-pig olfactory cortex in vitro. Higher concentrations slightly depolarised these neurones and reduced their input resistance (Ri), presumably a spontaneous activation of the inhibitory conductance. The excitatory potentials were also depressed. Ketamine, halothane and urethane doubled the i.p.s.c. duration. Higher concentrations depressed synaptic activity and the action potential, as did lignocaine. Ketamine also increased Ri. These results confirm the idea that these compounds produce anaesthesia by prolonging inhibition (accompanied by a depression of the e.p.s.p. with some anaesthetics).