The cannabinoid receptor 1 (CB1) is expressed ubiquitously throughout the central nervous system (Mackie, 2008), hence it is difficult to dissect the precise role of specific brain regions and cell-types in mediating Δ9-tetrahydrocannabinol (THC) addiction. Recently, deletion of CB1 from D1+ MSNs was found to modestly affect behavioral responses to THC, including blunted effects in THC-induced hypolocomotion, hypothermia, and analgesia (Monory et al., 2007). It would be interesting to evaluate cannabinoid receptor function in D2+ MSNs since these MSNs express endocannabinoid-mediated long-term depression (eCB-LTD), which requires dopamine D2-receptor activation (Kreitzer and Malenka, 2007).
