Melatonin increases proliferation of cultured neural stem cells obtained from adult mouse subventricular zone Introduction The discovery of a continuous neurogenesis in two areas of the adult brain, the subgranular zone (SGZ) in the dentate gyrus of the hippocampus [1] and the anterior part of the subventricular zone (SVZ) lining the lateral ventricle [2], changed the previous concept of the mammalian adult nervous system and led to the new theory that regeneration of neurons may occur throughout life. Adult neurogenesis is a process that leads not only to the generation of new neurons from adult neural stem cells but also functional integration of these new neurons into the mature neuronal circuit [3]. Because the proliferation and differentiation of the immature precursor cells (neural stem cells) are dynamically regulated by various hormones and growth factors under physiological and pathological conditions, the identifica- tion of signaling molecules that regulate neural stem cell activities may contribute to the understanding of neural ontogeny and to the development of new growth factor agents for the treatment of certain neurological diseases. Melatonin, or 5-methoxy-N-acetyltryptamine, is a circa- dian rhythm hormone secreted mainly by the pineal gland. In mammals, melatonin is critical for the physiological functions of the neuroimmuno-endocrine system such as sleep–wake cycle [4], pubertal development [5] and seasonal adaptation [6]. Although melatonin possesses multiple physiological functions, the antioxidant action has at- tracted much attention recently [7]. Via its free radical– scavenging mechanisms, melatonin prevents neuronal cell death induced by 6-hydroxydopamine [8], 1-methyl-4- phenylpyridinium ion (MPP+) [9], amphetamine [10, 11], b-amyloid protein [12] and kainic acid [13]. Increasing evidence suggests that melatonin might be an interesting agent in the context of neurogenesis. However, the role of melatonin in the regulation of neurogenesis is not clear. Melatonin enhances neurogenesis in embryos, but no data on adult neural precursor cells from the subven- tricular zone have been revealed [14, 15]. In addition, embryonic and adult neural stem cells have distinct properties. For example, embryonic stem cells are commit- ted to form neurons, whereas adult neural stem cells predominantly generate astrocytes [16, 17]. Melatonin signaling can regulate proliferation and neuronal differen- tiation of embryonic neural stem cells across a wide range of concentrations including pharmacological doses (10 )3 – 10 )1 mm) [14]. In this study, we examined the effects of melatonin on the proliferation and differentiation of progenitor cells from the high-level adult neurogenesis area, SVZ. Because stem cell replacement is thought to play an important therapeutic role in neurodegenerative diseases, melatonin Abstract: Melatonin, a circadian rhythm–promoting molecule secreted mainly by the pineal gland, has a variety of biological functions and neuroprotective effects including control of sleep–wake cycle, seasonal reproduction, and body temperature as well as preventing neuronal cell death induced by neurotoxic substances. Melatonin also modulates neural stem cell (NSC) function including proliferation and differentiation in embryonic brain tissue. However, the involvement of melatonin in adult neurogenesis is still not clear. Here, we report that precursor cells from adult mouse subventricular zone (SVZ) of the lateral ventricle, the main neurogenic area of the adult brain, express melatonin receptors. In addition, precursor cells derived from this area treated with melatonin exhibited increased proliferative activity. However, when cells were treated with luzindole, a competitive inhibitor of melatonin receptors, or pertussis toxin, an uncoupler of Gi from adenylate cyclase, melatonin-induced proliferation was reduced. Under these conditions, melatonin induced the differentiation of precursor cells to neuronal cells without an upregulation of the number of glia cells. Because stem cell replacement is thought to play an important therapeutic role in neurodegenerative diseases, melatonin might be beneficial for stimulating endogenous neural stem cells. Areechun Sotthibundhu 1 , Pansiri Phansuwan-Pujito 2 and Piyarat Govitrapong 1,3 1 Center for Neuroscience, Faculty of Science, Mahidol University, Bangkok, Thailand; 2 Department of Anatomy, Faculty of Medicine, Srinakharinwirot University, Bangkok, Thailand; 3 Research Center for Neuroscience, Institute of Molecular Biosciences, Mahidol University, Salaya, Nakornpathom, Thailand Key words: adult stem cell, melatonin, MT1- melatonin receptor, neurogenesis, proliferation, subventricular zone (SVZ) Address reprint requests to Piyarat Govitra- pong, Research Center for Neuroscience, Institute of Molecular Biosciences, Mahidol University, Salaya, Nakornpathom 73170, Thailand. E-mail: grpkk@mahidol.ac.th Received March 31, 2010; accepted June 4, 2010. J. Pineal Res. 2010; 49:291–300 Doi:10.1111/j.1600-079X.2010.00794.x Ó 2010 The Authors Journal of Pineal Research Ó 2010 John Wiley & Sons A/S Journal of Pineal Research 291 Molecular, Biological, Physiological and Clinical Aspects of Melatonin