Pressure reversal of the effect of urethane on the evoked somatosensory cortical response in the rat.

1 The cerebral response evoked by stimulation of the forepaw in the rat shows an increase in latency and decrease in the amplitude of its initial components as anaesthetic dose (urethane) is increased. 2 These changes are reversed if the ambient pressure is increased with helium and the electrocorticogram shows an increase in basic frequency. 3 The dose of urethane needed to prevent reflex response to tail stimulation is increased as pressure increases. 4. The implications of these behavioural and somatosensory responsiveness changes as pressure is increased are discussed.