In our study of the hippocampal transcriptome (Zhou et al., 2011) of cocaine addicts and alcoholics, we did not observe significant expression changes for some of the genes that have previously been shown to be altered in striatum, such as CART, FOSB, CdK5, NFκB, and HOMER. These differences may be a manifestation of brain region-specific changes or may also be the result of stage-specific alterations in response to drug exposure because the rodent studies were performed following relatively short-term drug exposure. However, in the cocaine addicts, we did observe expression changes in genes important for hippocampal functions, such as LTP. Hippocampal functions related to short- and long-term memory processes involve synaptic plasticity, and drug-associated learning and memories are important in craving. The hippocampus also directly projects excitatory efferents to the NAc and can also activate dopaminergic neurons of the ventral tegmental area, further implicating its involvement in drug-induced changes of neural plasticity. The genes involved in LTP include specific ionotropic and metabotropic glutamatergic receptors, calcium signaling-related proteins such as calmodulin, calcium/calmodulin-dependent protein kinase, protein phosphotase, adenylate cyclase, protein kinase A
