C mechanical nociceptive neurons in the crotaline trigeminal ganglia.

Using 32 Crotaline snakes, Trimeresurus flavoviridis, intrasomal recordings were made from 44 neurons of the trigeminal ganglia in vivo. They were 10 C neurons from 9 snakes and 34 A-delta mechanical nociceptive neurons from 23 snakes. 5 of the 10 C neurons were identified as mechanical nociceptive neurons. The neurons were labeled with iontophoretically injected HRP. Each of the 5 C nociceptive neurons had one receptive field, on which 1 spike was elicited by pricking the skin or mucosa with a pin. They were sensitized after repeated stimulation. The fields were insensitive to thermal stimulation. No background discharge was observed. Average conduction velocity was 0.95 m/s (+/- 0.4 S.D., n = 5). Mean resting potential was -62.5 mV (+/- 6.0 S.D., n = 4), and mean action potential amplitude was 88.0 mV (+/- 10.9 S.D., n = 4). Two somata were successfully visualized with HRP (22 microns x 20 microns, 20 microns x 18 microns). Total lengths of labeled axons were 1260 and 1480 microns peripherally to the edge of the section, and 1810 and 770 microns centrally. Neither of the neurons had branching of the peripheral or central axons in the ganglion.