Pavlovian conditioning of multiple opioid-like responses in mice

Department of Human Genetics, University of Chicago, 920 E. 58th Street, Chicago, IL 60637, USA.
Drug and alcohol dependence (Impact Factor: 3.42). 08/2009; 103(1-2):74-83. DOI: 10.1016/j.drugalcdep.2009.03.016
Source: PubMed


Conditional responses in rodents such as locomotion have been reported for drugs of abuse and similar to the placebo response in humans, may be associated with the expectation of reward. We examined several conditional opioid-like responses and the influence of drug expectation on conditioned place preference and concomitant conditional locomotion. Male C57BL/6J mice were conditioned with the selective mu opioid receptor agonist fentanyl (0.2mg/kg, i.p.) in a novel context and subsequently given a vehicle injection. In separate experiments, locomotor activity, Straub tail, hot plate sensitivity, and conditioned place preference (CPP) were measured. Mice exhibited multiple conditional opioid-like responses including conditional hyperlocomotion, a conditional pattern of opioid-like locomotion, Straub tail, analgesia, and place preference. Modulating drug expectation via administration of fentanyl to "demonstrator" mice in the home cage did not affect the expression of conditioned place preference or the concomitant locomotor activity in "observer" mice. In summary, Pavlovian conditioning of an opioid in a novel context induced multiple conditional opioid-like behaviors and provides a model for studying the neurobiological mechanisms of the placebo response in mice.

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    • "Following OXY training, OXY-CPP (D8-D1 time) loaded onto the same factor as change in distance and rotations for both strains (Tables 2A,B). Opioid-induced rotations (Figure 1A), or " circling " is a stereotypic behavior that is induced by opioid administration (Iwamoto and Way, 1977; Morihisa and Glick, 1977; Seidel et al., 1979; Mickley et al., 1990; Bryant et al., 2009; Hodgson et al., 2010) and its behavioral pattern can be expressed as a conditioned opioid-like placebo response (Bryant et al., 2009). Our observations indicate that mice expressing drug-free "

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    • "1977; Morihisa and Glick. 1977; Seidel et al. 1979; Mickley et al. 1990; Bryant et al. 2009; Hodgson et al. 2010) and its behavioral pattern can be expressed as a conditioned opioid-like placebo response (Bryant et al. 2009). Our observations indicate that mice expressing drug-free conditioned opioid reward behave in a manner that is similar to having received an opioid injection. "
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