PET imaging of neurogenic activity in the adult brain: Toward in vivo imaging of human neurogenesis.

Neural stem cells are present in 2 neurogenic regions, the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG), and continue to generate new neurons throughout life. Adult hippocampal neurogenesis is linked to a variety of psychiatric disorders such as depression and anxiety, and to the therapeutic effects of antidepressants, as well as learning and memory. In vivo imaging for hippocampal neurogenic activity may be used to diagnose psychiatric disorders and evaluate the therapeutic efficacy of antidepressants. However, these imaging techniques remain to be established until now. Recently, we established a quantitative positron emission tomography (PET) imaging technique for neurogenic activity in the adult brain with 3'-deoxy-3'-[18F]fluoro-L-thymidine ([18F]FLT) and probenecid, a drug transporter inhibitor in blood-brain barrier. Moreover, we showed that this PET imaging technique can monitor alterations in neurogenic activity in the hippocampus of adult rats with depression and following treatment with an antidepressant. This PET imaging method may assist in diagnosing depression and in monitoring the therapeutic efficacy of antidepressants. In this commentary, we discuss the possibility of in vivo PET imaging for neurogenic activity in adult non-human primates and humans.