Tooth pulp input to the spinal trigeminal nucleus: A comparison of inhibitions following segmental and raphe magnus stimulation

In rats and cats anaesthetized with urethane a comparison was made of the inhibitory effects of raphe magnus (NRM) and segmental (facial skin) stimulation on neurones in nucleus caudalis excited by tooth pulp stimulation. The upper and lower ipsilateral incisor teeth were used in rats (176 neurones) and the corresponding canine teeth in cats (34 neurones). The recording sites were located in all layer of nucleus caudalis and in the underlying reticular formation. Both the evoked responses and the conditioning effects were similar in the two species. Both forms of conditioning inhibited about half the neurones tested but only a small proportion was influenced from both sources. NRM stimulation had almost identical effects on neurones driven from upper teeth or from lower teeth and tended to act on those cells with longer latencies. Segmental stimulation influenced the majority of shorter latency cells and produced greater inhibitions of upper tooth pulp neurones. Diffuse noxious inhibitory controls were also observed for certain neurones.