Receptor Subtypes in Opioid and Stimulant Reward

Abstract

Studies of the behaviourally-reinforcing actions of opioid and stimulant drugs of abuse are reviewed in an attempt to identify their reward-related brain receptors. We focus on data generated by drug self-administration, brain stimulation reinforcement, and conditioned place preference paradigms. A consistent body of evidence supports a role for μ and δ, but not K, receptors in opioid reward. Stimulant reward apparently involves both D₁ and D₂ receptors; the data favour D₂ mediation of stimulant drug reinforcement with a permissive or modulatory role for D₁ receptors. The reward-relevant opioid and dopamine receptors, as well as the cannabinoid (marijuana) receptor, share the ability to couple G_i proteins that mediate inhibition of adenylate cyclase and stimulation of K⁺ conductance. These signal transduction mechanisms thus may be generally implicated in the reinforcing properties of diverse drugs of abuse.