Recently, researchers genetically profiled the cocaine context-dependent, c-Fos activated neurons in rats using immunolabeled fluorescence activated cell sorting (FACS) and showed that the c-Fos+ neurons are enriched in a D1+ MSN gene, prodynorphin (Pdyn), but have lower levels of D2 and A2A, both D2+ MSN genes (Guez-Barber et al., 2011), suggesting that the c-Fos+ activated neurons consist primarily of D1+ MSNs. Furthermore, this group previously showed that c-Fos expressing MSNs are important for this context-dependent sensitization, as ablation of these neurons abolishes this behavioral phenotype (Koya et al., 2009). Although previous data showed that the cocaine context-dependent induction of c-Fos occurs in both D1+ and D2+ MSNs in rats, the more recent results correspond to findings in which deletion of c-Fos selectively from D1+ MSNs blunts cocaine-induced locomotor sensitization in mice (Zhang et al., 2006). Furthermore, this group found that deletion of c-Fos in D1+ MSNs blunts the dendritic spine changes normally induced by cocaine in the NAc, indicating a role for c-Fos in mediating these synaptic plasticity changes. Finally, the group observed no change in the induction of cocaine
