THE CONTRIBUTION OF ASTROCYTES TO THE F-18 2-DEOXYGLUCOSE SIGNAL IN PET ACTIVATION STUDIES

With the development of functional brain imaging techniques such as Po sitron Emission Tomography (PET) and functional Magnetic Resonance Ima ging (fMRI) it has become possible to visualize brain areas that are a ctivated by a variety of sensory, motor or cognitive tasks, This techn ological progress has permitted a kind of in vivo functional neuroanat omy which has led to the identification of neural circuits subserving specific brain functions, Metabolic processes linked to neuronal activ ity - such as blood flow, glucose utilization and oxygen consumption - provide the signals detected with most functional brain-imaging techn iques, These metabolic indices have been examined in a variety of psyc hiatric and neurological disorders, This article focuses on the use of (F-18)fluoro-2-deoxyglucose (FDG)-PET in the study of psychiatric dis orders; it is mainly intended to bring a novel perspective, based on r ecent experimental data, on the cellular and molecular mechanisms that underlie the FDG-based PET imaging. These new observations point to a critical role of a particular glial cell type, the astrocyte, in coup ling neuronal activity to glucose utilization, Indeed it appears that in response to glutamate released by active neurons, glucose is predom inantly taken up by specialized astrocytic processes, the end-feet, wh ich surround brain capillaries; glucose is then metabolized to lactate , which provides a preferred energy substrate for neurons, These data support the notion that astrocytes markedly contribute to the FDG-PET signal, This perspective may also provide renewed insights for the int erpretation of FDG-PET studies in psychiatric disorders.