Differences between nerve terminal impulses of polymodal nociceptors and cold sensory receptors of the guinea-pig cornea

1. Extracellular recording techniques were used to stud;v nerve terminal im pulses (NTIs) recorded from single polymodal nociceptors and cold-sensitive receptors in guinea-pig cornea isolated in vitro. 2. The amplitude and time course of NTIs recorded from polymodal nociceptor s was different from those of cold-sensitive receptors. 3. Bath application of tetrodotoxin (1 muM) changed the time course of spon taneous NTIs recorded from both polymodal and cold-sensitive receptors. 4. Bath application of lignocaine (lidocaine; 1-5 mM) abolished all electri cal activity. 5. Local application of lignocaine (2.5 and 20 mM) through the recording el ectrode changed the time course of the NTIs recorded from polymodal nocicep tors hut not that of NTIs recorded from cold-sensitive nerve endings. 6. It is concluded that action potentials propagate actively in the sensory nerve endings of polymodal nociceptors. In contrast, cold-sensitive recept or nerve endings appear to he passively invaded from a point more proximal in the axon where the action potential can fail or be initiated.