Thalamic and mid-brain responses to dental pulp afferent messages in awake cats

1. Central projections of messages evoked by dental pulp stimulation have been searched for in awake cats and recorded at unitary level. A head-top frame screwed to the skull served to fix the animal in the stereotaxic instrument precisely and in the usual orientation. 2. Three types of responses could be distinguished, each with characteristic thalamic localization: --one was of the specific type: it occurred at short latency, followed rapid rates of stimulation, and was localized in VPM and SG; --a second type had longer latency, did not follow rapid rates of stimulation, was frequently bilateral, and was localized in VPM, CM-Pf and Posterior Group; --the third type was a complex response, exhibiting inhibitory and excitatory phases; extremely labile, it disappeared during wakefulness; it was found in LP and CM-Pf. 3. The responses elicited by dental pulp stimulation and recorded in the periaqueductal grey matter mostly originated from face muscle messages provoked by the jaw opening reflex. 4. The possible contributions to pain perception made by each of the different thalamic responses is discussed, as well as the adequacy of dental pulp stimulation for producing a purely nociceptive signal.