Tooth pulp neurons in the caudal medulla oblongata of the cat

The medulla oblongata caudal to the obex was explored for neurons responsive to tooth pulp (TP) stimulation in cats. Four different subclasses of TP neurons were found. The latter included TP specific (TPS) neurons, trigeminal wide dynamic range (trigeminal WDR) neurons with TP input, trigeminal subnucleus reticularis ventralis (trigeminal SRV) neurons with TP input and convergent reticular formation (convergent RF) neurons with TP input. TPS neurons were located in the dorsal marginal rim of the trigeminal subnucleus caudalis, i.e., in the marginal layer or the outer zone of substantia gelatinosa. WDR neurons with TP input were found in the neck region of medullary dorsal horn which corresponds to the lateral part of subnucleus reticularis dorsalis (SRD). Trigeminal SRV neurons with TP input were located in the lateral part of SRV. Convergent RF neurons with TP input were found in the middle third of the caudal bulbar RF consisting of SRD and SRV. Both TPS neurons and WDR neurons with TP input included trigeminothalamic neurons as evidenced by the antidromic activation from the nucleus ventralis posteromedialis of the contralateral thalamus. A significant proportion of both trigeminal SRV and convergent RF neurons with TP input were antidromically activated by stimulation of the nucleus centralis lateralis of the contralateral thalamus. The former two subclasses may subserve the sensory-discriminative aspect of toothache, while the latter two subclasses, the emotional-motivational aspect.