Drug Cues, Conditioned Reinforcement, and Drug Seeking: The Sequelae of a Collaborative Venture With Athina Markou

REM sleep deprivation before extinction or reinstatement alters methamphetamine reward memory via D1-like dopamine receptors

We aimed to determine whether REM sleep deprivation (RSD) affects extinction and reinstatement of methamphetamine (METH) reward memory in male rats and also to evaluate the possible role of dopamine D1-like and D2-like dopamine (DA) receptors in these processes. Male rats were trained to acquire METH-induced place preference (2 mg/kg, i.p.). METH reward memory was then reinstated following a 10-day extinction period. The animals underwent a 72-hour sleep deprivation episode by multiple platforms method (in separate groups), either before the extraction or before the reinstatement of METH reward memory. The animals received SCH 23390 (0.01 or 0.05 mg/kg, i.p.) or sulpiride (20 or 60 mg/kg, i.p.) as antagonists of D1-like and D2-like DA receptors, respectively, either immediately following each daily extinction session or before the reinstatement of METH-seeking behavior. The RSD episode postponed extinction and facilitated reinstatement of METH reward memory. Administration of SCH 23390, but not sulpiride, facilitated METH extinction and decreased reinstatement of the extinguished METH-seeking behavior. Moreover, locomotor activity was not affected by METH and/or the RSD paradigm. The results would seem to suggest that the D1-like, but not the D2-like, DA receptors may be involved in the extinction and reinstatement of the extinguished METH reward memory in RSD animals. Nonetheless, more investigations are needed to elucidate the exact mechanisms involved.

A2AR-D2R Heteroreceptor Complexes in Cocaine Reward and Addiction

The concept of allosteric receptor-receptor interactions in G protein-coupled receptor homo- and heteroreceptor complexes in which they physically interact provides a new dimension to molecular integration in the brain. The receptor-receptor interactions dynamically change recognition, pharmacology, signaling, and trafficking of the participating receptors. Among the receptor complexes, disruption of the A2A receptor-dopamine D2 receptor (A2AR-D2R) complex by an A2AR agonist has been shown to fully block the inhibition of cocaine self-administration. Cocaine induced pathological A2AR-D2R-Sigma1R complexes may form a long-term memory with a strong and permanent D2R brake, leading to cocaine addiction. These heteroreceptor complexes can potentially be targeted for future pharmacotherapy of cocaine addiction by using heterobivalent compounds or A2AR-D2R receptor interface-interfering peptides that disrupt the A2AR-D2R-Sigma1R complexes.