Cocaine-Induced Dendritic Spine Formation in D1 and D2 Dopamine Receptor-Containing Medium Spiny Neurons in Nucleus Accumbens

Psychostimulant-induced alteration of dendritic spines on dopaminoceptive neurons in nucleus accumbens (NAcc) has been hypothesized as an adaptive neuronal response that is linked to longlasting addictive behaviors. NAcc is largely composed of two distinct subpopulations of medium-sized spiny neurons expressing high levels of either dopamine D1 or D2 receptors. In the present study, we analyzed dendritic spine density after chronic cocaine treatment in distinct D1 or D2 receptor-containing medium-sized spiny neurons in NAcc. These studies made use of transgenic mice that expressed EGFP under the control of either the D1 or D2 receptor promoter (Drdl-EGFP or Drd2-EGFP). After 28 days of cocaine treatment and 2 days of withdrawal, spine density increased in both Drdl-EGFP-and Drd2-EGFP-positive neurons. However, the increase in spine density was maintained only in DrdlEGFP-positive neurons 30 days after drug withdrawal. Notably, increased ∆FosB expression also was observed in Drdl-EGFP-and Drd2-EGFP-positive neurons after 2 days of drug withdrawal but only in Drdl-EGFP-positive neurons after 30 days of drug withdrawal. These results suggest that the increased spine density observed after chronic cocaine treatment is stable only in D1receptor-containing neurons and that ∆FosB expression is associated with the formation and/or the maintenance of dendritic spines in D1 as well as D2 receptor-containing neurons in NAcc.