Figure 2. Effect-time profile of the electroencephalographic effect (0.5-4.5 Hz) during and after a stepwise infusion of remifentanil (top), GR90291 (middle), or physiologic saline (bottom) in representative rats. Open circles = measured concentrations of remifentanil in the blood; filled circles = measured concentrations of GR90291 in the blood. (Note that the concentrations of remifentanil and GR90291, in the top and middle, differ by three orders of magnitude as they are given in ng/ml and [micro sign]g/ml, respectively).