Figure 1. Specimen recording showing the effect of loperamide on the mechanosensitivity of an unmyelinated afferent (AE49.02C) recorded from a spinal nerve lesioned animal 9 days post injury.

Vertical bars indicate occurrence of an action potential (AP). Arrows indicate von Frey hair application to determine mechanical threshold. Grey bars indicate tonic suprathreshold stimulation (5 s) with an 8 g von Frey hair. A) Responses to mechanical tests at baseline. In the two test sequences for baseline testing, the afferent responded to 2/2 trials of stimulation with a 6 g von Frey hair (but not to the next lower 4 gm von Frey hair, data not shown), and suprathreshold stimulation with 8 g von Frey hair induced a total of 15 and 14 action potentials in the first and second test sequence, respectively. Insets show occurrence of action potential recorded during suprathreshold stimulation at higher time resolution. On the right, all AP waveforms recorded during baseline testing are shown superimposed. B) Mechanical responses after injection of a cumulative 5 µg dose of loperamide (1.25 µg followed by 3.75 µg). The von Frey threshold increased to 10 g, and the afferent became unresponsive to tonic stimulation with 8 g. In the second test sequence, mechanical von Frey threshold was still 10 g. Responses to 8 g von Frey hair stimulation were not tested.