In another study, Enoch and coworkers147 reported that hippocampal glutamate receptor subunit gene expression levels differed between alcoholics, cocaine addicts, and healthy controls. Specifically, Glua4, Gluk3, and mGlu4 expression was significantly higher in alcoholics, relative to both controls and cocaine addicts; Glun2b expression was higher in both alcoholics and cocaine addicts, relative to control levels; and Glun2d and mGlu3 was upregulated in alcoholics while being downregulated in cocaine addicts, relative to control levels.147 Substantial changes of glutamate receptor subunit gene expression in the hippocampal dentate gyrus and to a lesser extent orbital frontal cortex, but not the dorsal-lateral prefrontal cortex, of alcoholics versus healthy controls was confirmed in another recent postmortem study.148 In particular, the data from the dentate gyrus revealed that alcoholics had higher expression levels of Glua2, Glua3, Gluk2, Gluk3, Gluk5, Glun1, Glun2a, Glun2c, Glun2d, and Glun3a; whereas only Glun3a expression was higher than controls in the orbital frontal cortex.148
