Date of Award
A placebo effect is a real and beneficial psychobiological phenomenon following the administration of a substance or procedure that has no inherent power to produce an effect. Nocebo effects, on the other hand are genuine and detrimental psychobiological phenomenon following the administration of and inert substance or procedure. These effects have been extensively studied but are not well understood. Central to the development of a placebo effect is the anticipation of benefit or the anticipation of harm. Indeed, expectancy and conditioning are thought to be the two primary mechanisms involved in the acquisition of the placebo effect. The neurotransmitter Dopamine (DA) is integral to expectancy and reward and as such has recently been considered a key player in the mechanisms of the placebo effect. Based on this line of inquiry this study sought to investigate the role DA might have in the development of the placebo effect as observed in pain using an animal (mouse) model. It was proposed that DA is involved in the acquisition and maintenance of the placebo effect. Specifically it was proposed that the DA agonist cocaine would enhance the magnitude and duration of the placebo analgesia and that the DA antagonists SCH23390 and eticlopride would together or separately block the acquisition of the placebo analgesia. These proposals were assessed by utilizing supra-spinal (hotplate) and spinal (tail flick latency) protocols. Results indicated that cocaine enhanced placebo analgesia in spinal but not supra-spinal measures and that the DA antagonists SCH23390 and eticlopride each contributed to the acquisition, rather than the blockade, of placebo analgesia in both spinal and supra-spinal models. In fact, the most profound effect was observed when both antagonists were administered together rather than separately on supra-spinal measures but not spinal measures resulting in an enduring nocebo effect contradicting all predictions. The novel results presented in this study raises more questions than they answer, warranting more detailed exploration of the mechanisms of DA and its relationship with placebo effects.
Brewer, Steve T., "The Influence of Dopamine on the Magnitude and Duration of the Placebo Effect" (2014). University of New Orleans Theses and Dissertations. 1905.