Decreased dorsolateral prefrontal N-acetyl aspartate in bipolar disorder

Background: N-acetyl aspartate (NAA) is an amino acid present in high conce ntrations in neurons and is thus a putative neuronal marker. In vivo proton magnetic resonance spectroscopy (IH MRS) studies have shown lower NAA conc entrations in patients with various neurodegenerative disorders, suggesting decreased neuronal number, size, or function. Dorsolateral prefrontal (DLP F) NAA has not been extensively assessed in bipolar disorder patients, but it could be decreased in view of consistent reports of decreased DLPF cereb ral blood pow and metabolism in mood disorders. We measured DLPF NAA in pat ients with bipolar disorder and healthy control subjects using in vivo IH M RS. Methods: We obtained ratios of NAA, choline, and myoinositol (ml) to creati ne-phosphocreatine (Cr-PCr) in bilateral DLPF 8-mL voxels of 20 bipolar pat ients (10 Bipolar I, 10 Bipolar II) and 20 age- and gender-matched healthy control subjects using H-1 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 w ith healthy control subjects. Conclusions: These preliminary data suggest that bipolar disorder patients have decreased DLPF NAA/Cr-PCr. This finding could represent decreased neur onal density or neuronal dysfunction in the DLPF region. (C) 2000 Society o f Biological Psychiatry.