Wei Lu1, Yelin Chen2. 1. Synapse and Neural Circuit Research Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: luw4@mail.nih.gov. 2. Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 26 Qiueyue Road, B6, Pudongxinqu, Shanghai 201203, China. Electronic address: chenyelin@mail.sioc.ac.cn.