Responses of neurons in rostral and caudal trigeminal nuclei to tooth pulp stimulation.

Using immobilized, lightly anesthetized cats, the responses of neurons in the nucleus principalis-subnucleus oralis and subnucleus caudalis regions of the sensory trigeminal complex were studied following electrical stimulation of the canine tooth pulp. Recording loci were verified histologically. Pulpal stimulation activated 122 cells in the rostral nuclei and 44 in the caudal one. Neurons in the two, spatially segregated, regions exhibited different, though overlapping distributions of response and receptive field properties. More specifically, the rostral region cells tended to have lower thresholds and to reach peak firing rates at lower stimulus intensities. Their peripheral fields were generally more restricted and more frequently homolateral. Following supra-maximal stimulation, they ordinarily had briefer initial spike latencies and their response bursts typically contained a greater number of spikes. These findings are consistent with the view that each of the regions operates in a different manner in the mediation of oro-facial pain.