Purinergic Signalling (2010) 6:429–445 to application of ATP, most probably via ionotropic P2X receptors [69, 70]. Another very recent study showed that cells of the PVZ along the lateral ventricle express functional P2X7 receptors [44]. But the present study is the first detailed functional in situ analysis of the purinergic system of a vertebrate PVZ. We found evidence that PVZ cells of larval X. laevis express a complex web of purinergic receptor subtypes, and that application of nucleotides induces characteristic [Ca2+]i transients in these cells. In various steps of the cell cycle [Ca2+]i increases are important [71] and more specifically it is also known that [Ca2+]i changes induced by P2Y receptor activation are essential for the transition from the G1 to the S and M phases of the cell cycle [72]. It might therefore be speculated that nucleotide-induced [Ca2+]i changes in neurogenic brain areas are deeply involved in the control of the proliferation of neuronal stem cells. The finding that P1, P2X as well as P2Y purinergic receptor subtypes are present in the PVZ of larval X. laevis, suggests that different nucleosides and nucleotides are likely involved in the fine-tuning of neuronal differentiation. Future detailed studies, specifically focusing on the interplay of the different purinergic receptor subtypes, but also on the interplay of the purinergic system with other regulatory systems will certainly bring more insight. As a last point, we would like to focus on the anatomical difference in the location of the telencephalic neurogenic areas between X. laevis and higher vertebrates. In embryos and adults of higher vertebrates, such as mammals, OB interneurons derive from a neuronal precursor cell pool situated at a certain distance from the OB. In embryos, interneurons migrate into the OB from the lateral ganglionic eminence. In adults, they derive from the subventricular zone and migrate to the OB following the rostral migratory stream. In some species, neuronal precursor cells have to cover distances up to several centimeters to reach the OB (for a review see [1]). In X. laevis a neuronal precursor cell pool directly borders the OB. Newborn interneurons can readily be integrated into the OB without traveling long distances. This anatomic peculiarity could certainly be of advantage for future studies dealing with basic mechanisms involved in the regulation of neurogenesis in general and the neuronal turnover in the OB in particular. In this context, it will of course be essential to investigate whether the purinergic system of the anterior telencephalon persists also in adult X. laevis, and whether in the adult system it is involved in the same physiological processes as in the larvae. Acknowledgments This work was supported by grants from the Research program, Faculty of Medicine, Georg-August-University Göttingen to I.M., and the DFG Research Center for Molecular Physiology of the Brain (CMPB, Project B1/9) to I.M. and D.S. 443 Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Lledo PM, Gheusi G, Vincent JD (2005) Information processing in the mammalian olfactory system. Physiol Rev 85:281–317 2. Hildebrand JG, Shepherd GM (1997) Mechanisms of olfactory discrimination: converging evidence for common principles across phyla. Annu Rev Neurosci 20:595–631 3. Endo T, Yoshino J, Kado K, Tochinai S (2007) Brain regeneration in anuran amphibians. Dev Growth Differ 49:121–129 4. 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