Figure 3.

Concentration- and time-related effect of various forms of tramadol to increase PPT. (A) (+)-tramadol (1 – 100 μM), (B) (-)-tramadol (1 – 100 μM), and (C) O-desmethyltramadol (0.1–100 μM) increased PPT in a concentration dependent manner. The time of administration of (+)-tramadol, (-)-tramadol and O-desmethyltramadol is indicated by an arrow. The symbols represent the mean values of PPT recorded from 6 segments at consecutive 5 min intervals; the positive error bars show the standard error of the mean (SEM).