Effects of morphine and barbiturate on the SI and SII potentials evoked by tooth pulp stimulation of rats.

The effects of morphine and barbiturate on the evoked potentials recorded from the primary and secondary somatic sensory areas of rats were investigated. The electric stimulation of contra- and ipsilateral tooth pulp (CTP and ITP) was used. The afferent impulse from dental pulp projected to the sensory face areas I and II (SI and SII). Morphine in doses of 2.5-10 mg/kg definitely inhibited SI and SII potentials evoked by CTP stimulation. Morphine also inhibited SII potentials evoked by ITP stimulation, while it rather enhanced SI potentials evoked by ITP stimulation. Pentobarbital sodium in doses of 4-16 mg/kg tended to inhibit SI potentials, but showed no effect or rather an enhancement on SII potentials evoked by CTP stimulation. Pentobarbital sodium enhanced SI and SII potentials evoked by ITP stimulation. In a large dose of 32 mg/kg, pentobarbital sodium inhibited SI and SII potentials evoked by ITP and CTP stimulations. The results suggest that SII is more closely related to the analgesia due to morphine than is SI.