The influence of hypnotics and tranquillizers on some evoked cortical potentials

Abstract

The influence of hypnotics (sodium thiopentone and sodium γ-oxybutyrate) and tranquillizers (chlorpromazine and Stelazine) on the direct cortical, transcallosal responses in the cortex and on responses in the bulbar pyramids has been investigated in acute experiments on 150 non-anaesthetized curarized rabbits and on 20 cats anaesthetized with chloralose. It was found that both the narcotics under investigation changed the positive components of the direct cortical response more than the negative ones. The transcallosal response was generally affected more by the drugs than the direct cortical response. These changes may have been caused by the direct cortical effect of the substances, not merely by the blockade of the afferent subcortical flow. Oxybutyrate and thiopentone induced similar changes, but oxybutyrate did not elicit a phase of deep depression of the potentials. The pyramidal response to peripheral stimulation showed high sensitivity to both the narcotics. After comparing the changes in this response with those in the primary cortical and antidromic pyramidal one, and in the intercortical response arising in the motor cortex after stimulation of the I somatosensory area, it was suggested that the narcotic drugs under investigation exerted a pronounced influence on the intercortical associative connections. Chlorpromazine and Stelazine, in doses not causing a hypotensive effect, did not greatly affect the direct cortical, transcallosal and associative pyramidal responses.