Physiological Properties of neurons in different parts of the cat trigeminal sensory complex.

The following points emerge from a systematic investigation of the 4 divisions of the cat trigeminal sensory complex. (1) The subnucleus oralis receives a large representation from the oral cavity, a region also represented in the 3 other divisions of the trigeminal sensory complex. (2) Nucleus principalis cells project heavily to the contralateral and to the ipsilateral ventroposterior thalamus. Ipsilateral projections are only from the oral cavity representation. (3) Units responding to noxious mechanical stimulation have been found at two different loci: the subnucleus caudalis for the entire trigeminal area, and subnucleus oralis for the oral cavity alone. (4) The dental pulp projects to the 4 divisions of the trigeminal sensory complex, but the heaviest projection was found in the rostral part (nucleus principalis and subnucleus oralis). (5) Three distinct types of post-synaptic responses were found to be evoked by dental pulp stimulation: (a) short latency, consistent and synaptically secure, (b) strongly variable latency, inconstant and easily fatigued and (c) a class showing progressive enhancement by progressive increase in stimulus intensity and repetition.