Decreased dorsolateral prefrontal N-acetyl aspartate in bipolar disorder

Background: N-acetyl aspartate (NAA) is an amino acid present in high concentrations in neurons and is thus a putative neuronal marker. In vivo proton magnetic resonance spectroscopy (1H MRS) studies have shown lower NAA concentrations in patients with various neurodegenerative disorders, suggesting decreased neuronal number, size, or function. Dorsolateral prefrontal (DLPF) NAA has not been extensively assessed in bipolar disorder patients, but it could be decreased in view of consistent reports of decreased DLPF cerebral blood flow and metabolism in mood disorders. We measured DLPF NAA in patients with bipolar disorder and healthy control subjects using in vivo 1H MRS. Methods: We obtained ratios of NAA, choline, and myoinositol (mI) to creatine-phosphocreatine (Cr-PCr) in bilateral DLPF 8-mL voxels of 20 bipolar patients (10 Bipolar I, 10 Bipolar II) and 20 age- and gender-matched healthy control subjects using 1H MRS. Results: DLPF NAA/Cr-PCr ratios were lower on the right hemisphere(p< .03) and the left hemisphere (p< .003) in bipolar disorder patients compared with healthy control subjects. Conclusions: These preliminary data suggest that bipolar disorder patients have decreased DLPF NAA/Cr-PCr. This finding could represent decreased neuronal density or neuronal dysfunction in the DLPF region.