Elevated metabolites within dorsolateral prefrontal cortex in rapid cycling bipolar disorder

Metabolites within the left dorsolateral prefrontal cortex (DLPFC) of six inpatients with bipolar II rapid cycling (RC) during various mood states (depressed, hypomanic, and euthymic), six depressed inpatients with non-RC bipolar disorder (BIPD), and six healthy controls (HC) were assessed by proton magnetic resonance spectroscopy (MRS). We hypothesized that glutamate/glutamine levels should be altered in RC compared with HC. Patients with RC in contrast to BIPD and HC exhibited elevated levels of N-acetylaspartate (NAA), choline (Cho), creatine (Cr), and glutamate/glutamine (Glx) during all mood states. The Glx levels of BIPD compared with HC did not differ significantly; the other metabolites were increased, though less than in RC patients. Our findings of elevated metabolites in patients with RC, especially Glx as a possible marker of cortical activity, indicate that increased neuronal activity may constitute an important neurobiological feature of RC.