Opioid expectation modifies opioid effects

Area of Science:

• Pharmacology
• Behavioral Neuroscience
• Psychopharmacology

Background:

• Drug tolerance is a complex phenomenon influenced by both the drug itself and the context of its administration.
• Predrug cues, through association, play a critical role in the development and expression of drug tolerance.
• Drug expectancy, a cognitive factor, is central to understanding how environmental cues impact drug effects.

Purpose of the Study:

• To investigate the role of drug expectancy, mediated by environmental cues, in the development of drug tolerance.
• To examine the applicability of a Pavlovian conditioning model in explaining tolerance to pharmacological agents.
• To determine if conditioned responses (CRs) opposite to the unconditioned response (UCR) contribute to tolerance.

Main Methods:

• Utilized a Pavlovian conditioning framework to model the acquisition of tolerance.
• Administered drugs and placebos to subjects with a history of drug exposure in contexts with familiar and novel cues.
• Manipulated environmental cues (putative conditional stimuli) to assess their impact on tolerance and conditioned responding.

Main Results:

• Tolerance was maximal when drug administration was preceded by expected cues, indicating the importance of drug expectancy.
• Animals exhibited compensatory responding to placebo when presented with familiar predrug cues, supporting a conditioning model.
• Neither tolerance nor conditioned responses were observed in the context of novel environmental cues.
• Manipulations of environmental cues affected the acquisition of tolerance, consistent with Pavlovian conditioning principles.

Conclusions:

• Drug expectancy, established through Pavlovian conditioning to environmental cues, is a significant determinant of drug tolerance.
• Conditioned responses that oppose the drug's effects can attenuate the unconditioned response, contributing to tolerance.
• Environmental cues present during drug administration are critical for the development of both tolerance and conditioned drug effects.