Fig. 5.

PK–PD analysis of the EEG effect of alfentanil in rats following in vivo μ-opioid receptor (MOP) knockdown with β-flunaltrexamine. Pretreatment with β-flunaltrexamine resulted in an approximately 60 % reduction of functional MOP receptors at 35 min and at 24 h post administration. A parallel shift in the concentration–effect relationship without a major change in maximum effect was observed. This reduction in functional receptors is consistent with the observation that the MOP receptor functions with a high receptor reserve. Reproduced from Garrido et al. [74]