Central projection of tooth pulp primary afferents in the cat.

Stimulation of the tooth pulp nerve, consisting of A-delta fibers, produces field potentials in the rostal subdivision of the nucles, tractus spinalis n. trigmini. Antidromic action potentials from the A-delta fibers of the tooth pulp nerve, and increased excitability of their central terminals after a preceding volley in other trigeminal branches, can be recorded only when the stimulating microelectrode is inserted into this region. Stimulation of tooth pulp afferents produces a jaw opening reflex, but no response in the facial musculature. This is in contrast to the action evoked from the A-alpha fibers in other trigeminal branches which elicit reflexes only in the facial musculature. Cortical responses, evoked by a volley in the tooth pulp nerve, can be recorded from the lateral part of the coronal gyrus. By systematic tracking with microelectrodes, three sources of negative field potentials with superimposed unit activity were found. The first is localized in the cortex of the coronal gyrus; the second and the third in the anterior ectosylvian and orbital gyri, the cortex of which infolds into the diagonal sulcus,