Conduction velocity (CV) of A- and C-fiber units recorded from the IAN. A: The antidromic spikes following 330 Hz electrical stimulation of the trigeminal spinal nucleus. Arrows indicate stimulus onset and closed circles represent antidromic spikes. B: The collision test for antidromic spikes. The open circle indicates the expected time point where antidromic spike should have appeared. C and D: Frequency histogram of CV in naive rats and IAN-transected rats, respectively. Inset figures in C and D indicate the receptive field in each unit.