Evidence for primary afferent depolarization of single tooth-pulp afferents in the cat.

1. Responses of single tooth-pulp afferents to electrical stimulation of sites in the trigeminal sensory nuclear complex were recorded from caine teeth in cats. 2. Changes in the excitability of the central terminals of a pulpal afferent after stimulation of other groups of sensory nerves were taken as evidence for changes in their polarization. 3. Electrical stimulation of nerves in other teeth resulted in raised excitability of the central terminals of pulpal afferents lasting up to 300 msec. The greatest effects were observed 30--100 msec after the conditioning stimulus. 4. Increased terminal excitability was also observed after the ipsilateral infraorbital nerve was stimulated. This occurred when only nerve fibres with conduction velocities in the A alpha range were excited. 5. Mechanical stimulation of a canine tooth produced increases in terminal excitability of pulpal afferents innervating the same tooth. 6. A similar effect was also observed after a brief pull on a group of ipsilateral mystacial vibrissae. 7. No evidence of decreases in the excitability of the central terminals of tooth-pulp afferents was obtained with any of the conditioning stimuli.