Reduced NAA Levels in the Dorsolateral Prefrontal Cortex of Young Bipolar Patients
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OBJECTIVE: Converging evidence implicates prefrontal circuits in the pathophysiology of bipolar disorder. Proton spectroscopy studies performed in adult bipolar patients assessing prefrontal regions have suggested decreased levels of N-acetylaspartate (NAA), a putative marker of neuronal integrity. In order to examine whether such abnormalities would also be found in younger patients, a 1H spectroscopy study was conducted that focused on the dorsolateral prefrontal cortex of children and adolescents with bipolar disorder. METHOD: The authors examined the levels of NAA, creatine plus phosphocreatine, and choline-containing molecules in the left dorsolateral prefrontal cortex of 14 bipolar disorder patients (mean age=15.5 years, SD=3, eight female) and 18 healthy comparison subjects (mean age=17.3, SD=3.7, seven female) using short echo time, single-voxel in vivo 1H spectroscopy. Absolute metabolite levels were determined using the water signal as an internal reference. RESULTS: Bipolar patients presented significantly lower NAA levels and a significant inverse correlation between choline-containing molecules and number of previous affective episodes. No differences were found for other metabolites. CONCLUSIONS: These findings suggest that young bipolar patients have decreased NAA levels in the dorsolateral prefrontal cortex, similar to what was previously reported in adult patients. Such changes may reflect an underdevelopment of dendritic arborizations and synaptic connections. These neuronal abnormalities in the dorsolateral prefrontal cortex of bipolar disorder youth are unlikely to represent long-term degenerative processes, at least in the subgroup of patients where the illness had relatively early onset.
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