Response properties of the periodontal mechanosensitive neurons in the thalamus of the cat: a comparison between the slowly adapting and rapidly adapting neurons.

Slowly adapting (SA) and rapidly adapting (RA) types of the periodontal mechanosensitive units (PM units) were recorded in the thalamus and their response properties were examined in the cat. Both types of the PM units were located in the medial area (PM area) of the nucleus ventralis posteromedialis (VPM) of the thalamus. The SA units were located in a rostro-medial part of the PM area, while the RA units were distributed in the caudo-lateral part. An incidence of the SA and RA units was 45.5 and 54.5%, respectively. The single-tooth units were found in 23.5% of the SA units and in 14.9% of the RA units, and they responded chiefly to mechanical stimulation of the contralateral canine tooth. The multi-tooth units of the SA type had smaller receptive fields than those of the RA type, because the majority of the RA units had their receptive fields at the bilateral and/or bimaxillary area. In total, the units having the contralateral receptive fields were also dominant in both adaptation types. The latency of the neuronal discharges to electrical stimulation of the receptive field was fairly shorter in the SA units than in the RA units. These findings suggest that the SA units of the thalamus receive periodontal inputs directly from the trigeminal nuclear complex (Vcomp) of the brain stem, while the RA units receive them polysynaptically from the Vcomp via other pathways.