THE EFFECT OF CERVICAL SPINAL SECTION ON THE ABILITY OF MORPHINE TO ELEVATE THE JAW JERK THRESHOLD TO ELECTRICAL STIMULATION OF THE TOOTH PULP IN CATS

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

The tooth pulp was stimulated in normal, full spinal section and hemisectioned preparations with either a single monophasic square wave pulse of 0.5-msec duration or a train of four such pulses at 64 Hz. The effect of morphine (2 mg/kg i.v.) upon the threshold voltages required to elicit the jaw jerk response was different in the three preparations. In animals with intact spinal cords, morphine was effective in elevating the jaw jerk threshold. In contrast, morphine had no effect in animals with full spinal section. In addition, in animals in which the cord was hemisectioned, morphine was less effective against tooth pulp stimulation on the side ipsilateral to the site of hemisection than on the contralateral side. These findings suggest that morphine may exert its effect on tooth pulp thresholds either directly or indirectly through a depressant action upon the caudal portion of the spinal nucleus of the trigeminal nerve.