438 Purinergic Signalling (2010) 6:429–445 Fig. 6 Responsiveness of OB and PVZ cells to purinergic receptor agonists. a Mean [Ca2+]i transients (±SEM) of all clearly identifiable responsive cells of an OB (red traces) and a PVZ (green traces). Traces originate from more than one tissue slice. b The mean peak amplitude of agonist-induced responses (±SEM) of cells of the OB and the PVZ were compared (red columns OB cells, green columns PVZ cells). [adenosine (100 μM), data from 170 OB cells and 236 PVZ cells from 6 slices of the anterior telencephalon; ADP (100 μM), 245 OB cells and 154 PVZ cells from three slices; ATP (50 μM), 1566 OB cells and 1303 PVZ cells from 28 and 23 slices, respectively; 2MeSATP (100 μM), 378 OB cells and 285 PVZ cells from five [Ca2+]i transients of OB cells (Fig. 8b, b2 and b3). Figure 8c (c1–c3) summarizes the results obtained from all amino acid- responding OB cells from various nose–brain preparations treated with 2MeSATP, ATP and suramin, respectively. Discussion The purinergic system employs extracellular purines and pyrimidines as signaling molecules [9]. In the nervous system, both neurons as well as glial cells have been shown to express various subtypes of purinergic receptors [14]. The purinergic receptors of many brain regions have been thoroughly characterized, and the effects of their activation intensively studied [14, 30]. However, the information available about the purinergic system of the OB and the neurogenic PVZ is rather limited. There is evidence for P1 receptors [16], P2X receptors (P2X2: [31–33]; P2X4: [34– 36]; P2X5: [37]; P2X6: [35, 38]; P2X7: [39]) and P2Y receptors (P2Y1: [40]; P2Y2: [33]) in the murine OB and slices; BzATP (50 μM), 213 OB cells and 93 PVZ cells from four and two slices, respectively; α,β-MeATP (50 μM), 310 OB cells and 198 PVZ cells from six and three slices, respectively; β,γ-MeATP (100 μM), 387 OB cells and 318 PVZ cells from seven and six slices, respectively; uridine (100 μM), 275 OB cells and 308 PVZ cells from six slices; UTP (100 μM), 335 OB cells and 324 PVZ cells from five slices]. (*p<0.05 and **p<0.01; unpaired t test). Abbrevia- tions: ADP adenosine-5′-diphosphate, ATP adenosine-5′-triphosphate, UTP uridine-5′-triphosphate; α,β-MeATP α,β-methylene-ATP, β,γ- MeATP β,γ-methylene-ATP, 2MeSATP 2-methylthio-ATP, BzATP, 3′- O-(4-benzoyl)benzoyl ATP for P2X receptors (P2X1-6: [41]; P2X2: [32]; P2X6: [35, 38]; P2X7: [39, 42–44]) in the murine PVZ. Ectonucleoti- dases, enzymes that are located at the cell surface and hydrolyze nucleotides to the respective nucleoside, have also been found in these areas [15]. The above evidence is almost exclusively based on mRNA and protein profiles. Pharmacological studies are almost completely missing, and the physiological relevance of the purinergic system in these brain regions is still elusive. Only two studies describe functional purinergic receptors in these brain regions. Astrocytes in the murine OB have been shown to express functional A2A and P2Y1 receptors [16], and cells of the PVZ of the murine lateral ventricles have been reported to express functional P2X7 receptors [44]. Here, we set out to describe the organization of the PVZ of larval X. laevis, and to functionally characterize the purinergic system of the OB and its neurogenic PVZ. Our suggestions about the possible physiological roles of the purinergic system in these two brain areas should aid future work dealing with these topics.