The action of stimulant and depressant agents on local cerebral impedance and circulation

Summary

The effect of typical stimulant and depressant drugs on local cerebral impedance patterns has been studied in unanesthetized, intact cats with indwelling electrodes. Blood flow variations have been deduced from changes in amplitude of the pulsatile electrical impedance recorded across the electrodes.

Amphetamine produced bradycardia and a selective increase in cortical impedance and blood flow. At subcortical sites there was a tendency toward decreased flow with minimally effective doses and increased flow with maximally effective doses. Caffeine also showed a similar, but less marked selective increase in cortical flow but with an accompanying tachycardia.

Sedation with pentobarbital was typically accompanied by generalized reduction in cerebral blood flow and tachycardia, except that the hypothalamus retained considerable vasomotor activity in the early post-drug period. Chlorpromazine, on the other hand, had little effect on general cerebral circulation but selectively depressed hypothalamic blood flow and vasomotor responsiveness. Ether anesthesia was associated with large increases in subcortical blood flow and little or no increase in cortical flow.

Stimulant and depressant drugs were compared with intravenously injected epinephrine and with natural states of alertness in their effects on local cerebral blood flow. Circulatory patterns after amphetamine did not resemble those of arousal or of epinephrine, and those of pento-barbital differed from the patterns of natural sleep.