Nature of glutamate alterations in substance dependence: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies.

Animal studies have reported the brain glutamatergic dysfunction in substance dependence. However, proton magnetic resonance spectroscopy (H-MRS) studies of glutamate in substance-dependent patients published contradicting results. In order to investigate the characteristics of brain glutamatergic alterations in substance-dependent patients, we conducted systematic reviews and meta-analyses of H-MRS studies that have investigated the glutamate, glutamine, and Glx (glutamate + glutamine) concentration in substance-dependent patients. Multiple databases were searched until Sep 10, 2020. Twenty-nine studies comprising 982 patients and 787 controls were included. There was significantly decreased glutamate level in dorsolateral prefrontal cortex in patients compared with controls. Higher glutamate levels in medial prefrontal cortex and basal ganglia region were also demonstrated in patients compared with controls. Subgroup analyses based on the substance type and abstinence period (short vs medium-term abstinence period) were performed. The results revealed Glx and glutamate concentrations in all investigated brain regions were not different in patients with any types of substance dependence compared with controls. The abstinence period had no effect on the glutamate levels. In summary, substance dependence is associated with glutamatergic dysfunction of prefrontal cortex and basal ganglia. Present findings partially support the hypothesis that addiction is associated with abnormal brain glutamatergic neurotransmission.