Blockade of the reticulospinal inhibitory pathway by anaesthetic agents.

1. Adult cats were decerebrated at the intercollicular level. The effect of the anaesthetic agents, pentobarbitone, paraldehyde, tribromethanol, chloralose and procaine on the reticulospinal inhibitory pathway, which produced inhibition of segmental reflex potentials, was analysed.2. The doses which blocked this inhibitory pathway did not exceed the doses required to produce surgical level anaesthesia with any of the drugs.3. After the reticular inhibition of the reflex potentials was abolished, the reflex potentials were augmented by reticular stimulation with a higher intensity. This was thought to be due to spread of current to the excitatory pathways which were not completely depressed by the anaesthetic agent.4. The resistance of the reticular facilitation of the reflex potentials to inhibition by these drugs after abolition of inhibition corresponded in general to the degree of excitement in intact mice produced by the same drugs.5. These findings seem to indicate that the preferential block of the reticulospinal inhibitory pathway may be an important neural mechanism for the excitement stage of anaesthesia.