Figure 3.

Amitriptyline reduces the magnitude of the nicotine effect on C-fibre excitability. Nicotine (10 µM) produces a robust increase in the electrical excitability of C-fibres as illustrated in panel Aa for three consecutive applications at 20 min intervals. There is no indication of tachyphylaxis. The inset to the right (Ab) shows an example of the C-fibre CAP recorded in response to supra-maximal stimulation. Amitriptyline (3 µM) substantially reduces the increase in excitability produced by nicotine (10 µM) as shown in the recording from a second isolated human nerve segment in B. At a concentration of 3 µM amitriptyline's action is restricted to an inhibition of the excitability increase brought about by nicotine (Ba), with only a small effect on the amplitude and latency to onset of the C-fibre response to supra-maximal stimulation (Bb, inset right).