mGluR5 upregulation and the effects of repeated methamphetamine administration and withdrawal on the rewarding efficacy of ketamine and social interaction.

Repeated, recreational ketamine (KE) or methamphetamine (MA) administration seldom produce neurotoxicity, while combining MA and KE administration have been thought to render changes in neural plasticity and motivational behavior. In this study, we sought to assess whether pre-exposure to multiple MA injections and withdrawal may affect low-dose KE-produced rewarding effects, social interaction behavior and its neurochemical underpinnings. A 10-day MA injections (2 mg/kg/day) and 10-day withdrawal regimen was found to cause reliable behavioral sensitization. While KE (1 mg/kg) induced weak conditioned place preference (CPP), pre-exposure to this MA-withdrawal regimen enhanced such KE CPP magnitude. This MA-withdrawal regimen also caused impairments in the social interaction behavior in the sociability, social novelty test. Compared with the mice undergoing the 10-day saline-withdrawal or MA regimen, mice receiving the 10-day MA-withdrawal regimen exhibited lower dopamine-releasing probability in the nucleus accumbens, inferring the MA-withdrawal regimen-primed preference for KE rewarding effects. Likewise, mice receiving the MA-withdrawal regimen had high expression in mGluR5 protein but unaltered EAAT3, Homer2 expression in hippocampal tissues. Pretreatment with MPEP, an mGluR5 antagonist, prevented the MA-withdrawal regimen-induced increment in the KE CPP magnitude and impairments in social interaction behavior. We, thus, conclude that repeated MA administration and abstinence may enhance KE rewarding effects and produce eminent deficits in social recognition and interest. And these effects correlate with the mGluR5 over-expression and modulation of the KE-stimulating effect on dopamine release.

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