A comparison of the response properties of periodontal mechanosensitive neurons in each relay nucleus from the trigeminal ganglion to the somatosensory cortex in the cat and rat

This is a review of the response properties of periodontal mechanosensitive (PM) neurons in each relay nucleus of the ascending pathway from the primary afferents (the trigeminal ganglion) to the primary somatosensory cortex in the cat and rat. The major characteristics are as follows: the great majority of cat and rat primary PM afferents adapt slowly to mechanical stimulation of the tooth and are sensitive to one tooth only (single-tooth neurons). The threshold intensities to tooth stimulation are less than 0.01 N. The incidence of slowly adapting and single-tooth neurons decreases and threshold intensities become higher, as PM information is relayed to higher relay nuclei of the brain. The receptive fields of PM neurons in the trigeminal ganglion and the trigeminal sensory complex are ipsilateral. However, the occurrence of thalamic PM neurons with contralateral receptive fields increases to about 50% in the cat and 100% in the rat. The difference in the projection side of thalamic neurons between the cat and rat might be related to species differences and/or specialization of mastication in each animal.