Response properties of the tooth pulp-driven neurons in the primary somatosensory cortex (SI) in the cat.

Physiological properties of the neurons responding to canine tooth pulp stimulation (tooth pulp-driven neurons : TPDNs) were studied by recording single unit activities from the primary somatosensory cortex (SI) in cats anesthetized with α-chloralose. Analysis was focused on the TPDNs receiving excitatory converging inputs from the whisker pad and/or masseteric nerve with special reference to the interaction among these inputs.The results are as follows:(1) Twenty-seven of 51 TPDNs in SI (530) were convergent type neurons.(2) Convergent type TPDNs showed the following characteristics in relation to conditioning and test stimuli applied to the tooth pulp and other peripheral sites:a) When supra- or subthreshold conditioning stimuli were applied to the whisker pad and test stimuli to the tooth pulp, the number of spikes evoked by the test stimuli was decreased. Suprathreshold conditioning stimuli produced a greater decrease than subthreshold ones. On the contrary, no effects were seen when the sites of conditioning and test stimuli were reversed.b) Suprathreshold conditioning stimuli applied to the masseteric nerve exerted no effects on the number of spikes evoked by the tooth pulp test stimuli, whereas it was decreased in the reverse combination of conditioning and test sites.These results suggest that TPDNs in SI play an important role both in the recognition of the sites being stimulated and in processing other pain information, including the referred pain.