THE EFFECTS OF MORPHINE, PENTOBARBITOL AND CHLORPROMAZINE ON BIOELECTRICAL POTENTIALS EVOKED IN THE BRAIN STEM OF THE CAT BY ELECTRICAL STIMULATION OF THE GINGIVA AND TOOTH PULP

¹ Department of Pharmacology, College of Medicine, University of Iowa, Iowa City, Iowa

The effects of morphine sulfate (1, 2 and 4 mg/kg), pentobarbital sodium (2.5, 5 and 10 mg/kg), chlorpromasine hydrochloride (1, 2 and 4 mg/kg) and saline (0.1, 0.2 and 0.4 ml/kg) on the responses evoked from the central tegmental fasciculus, the dorsal tegmentum of the mesencephalon and the spinal trigeminal tract by gingival and tooth pulp stimulation were studied. In the central tegmental fasciculus, morphine had no significant effect on responses evoked by either type of stimulus. Pentobarbital and chiorpromazine significantly depressed both responses. In the dorsal tegmentum, both responses were significantly depressed by morphine, but this effect was not dose related. Pentobarbital significantly depressed both respouses in a dose-related manner. Chlorpromazine had no effect on the response elicited by gingival stimulation but depressed that produced by tooth pulp stimulation. In the spinal trigeminal tract, morphine had no effect on the responses evoked by either mode of stimulation. Pentobarbital and chiorpromazine slightly depressed the responses. The responses in the spinal trigeminal tract increased with time in the absence of drug. Had saline not been used to monitor the stability of the preparation an incorrect interpretation would have been placed on the results obtained with the recordings from the spinal trigeminal tract. The proper assessment of drug effects on bioelectrical responses is impossible without this control.