Introduction 1 2 3 4 5 10 11 13 14 15 2+ i 2+ i 16 17 18 2+ 2+ i 19 20 1 Fig. 1 Purine-induced signaling pathway involves the activation of P1 adenosine and P2 purinergic receptors and purine hydrolysis by ectonucleotidases. The scheme demonstrates purinergic receptor activity present in glia-glia, neuron-glia, and neuron-neuron interaction during neurogenesis as well as in the metabolism of the adult brain  In this review article, we shall discuss the roles of purinergic signaling in neurogenesis such as cell cycle control during neural progenitor proliferation and differentiation as well as in maintaining physiology of neurons and glial cells and the involvement of purinergic receptors in pathophysiology. In addition, we shall outline state-of-the-art approaches used in investigation of P2 receptor function in physiological processes such as the use of antisense oligonucleotides, generation of knockout animals, and identification of new purinergic receptor subtype-selective drugs. Study of purinergic receptor function during in vitro differentiation 21 2+ 22 23 2+ i 24 25 26 29 30 31 32 33 3 4 1 2 34 35 36 37 38 1 2 4 2 6 38 39 1 2 2 40 42 40 43 44 3 7 2+ i 41 45 46 1 2+ i 2 1 2+ i 1 47 1 48 1 2 47 49 Expression of purinergic receptors during development of the central nervous system 2+ i 50 51 2+ 1 2+ 25 52 53 54 55 56 59 3 7 58 2 56 2/3 3 56 60 3 61 7 7 62 63 7 7 2+ 64 5 65 3 4 5 7 1 6 58 66 25 2+ i 1 67 68 1 69 1 57 1 2 57 Functional interactions between neurons and glia: a physiological overview 70 71 72 73 74 75 76 77 71 78 79 81 71 82 85 ATP release and degradation, connecting adenosinergic and purinergic systems 86 87 88 89 22 90 91 1 92 93 94 95 96 97 7 98 101 102 91 103 1 104 105 20 ATP-mediated neuron-glia signaling 91 2+ 106 107 1–6 7 108 109 110 111 112 2+ 113 114 2+ 115 2+ i 2+ 1 116 117 1 4 7 59 4 5 118 119 120 121 122 123 124 53 3 3 12 Neuroprotection 7 125 126 127 1 128 Neuroimmune interactions 7 7 129 130 131 7 132 133 134 7 135 136 135 7 109 Neurological disorders Epilepsy 2+ 2+ i 137 138 2 4 139 A 2 4 139 7 B 7 140 B 140 A 141 142 139 Pain 2 3 143 145 3 146 147 3 148 3 2 3 148 149 3 4 4 150 4 150 4 Alzheimer’s disease 151 152 7 153 7 154 1 155 1 1 1 156 Ischemia/hypoxia 157 157 160 2 4 161 7 162 163 7 163 7 7 164 1 165 2,4,7 1 Trauma and axotomy 166 3 167 3 167 168 7 2+ i 168 1 2 169 166 2 1 170 2 2 171 172 D ATP-induced effects on cell cycle progression 173 174 175 176 177 2+ 178 179 180 181 182 183 184 c-fos c-jun 185 186 187 188 189 190 191 192 193 49 2+ i Pharmacological approaches 1 2 2 38 One possible approach towards a subtype-specific inhibitor would be based on results from P2 receptor structure determination. Using site-directed mutagenesis it has been possible to understand which amino acids are involved in ATP binding and to identify allosteric sites in purinergic receptors. The knowledge obtained on location and structural features of ligand and inhibitor binding sites is used in rational based drug design of selective purinergic subtype antagonists. Alternatively, combinatorial libraries formed by vast amounts of possible ligands can be employed for discovery of subtype-specific inhibitors. 2 3 3 3 2 3 3 2 3 149 N 6 1 194 1 195 196 2 O 32 197 2 198 Conclusion P2 receptor function is involved in most physiological processes and participates in neurotransmission in the CNS. Results obtained with mouse ES and P19 EC and neural progenitor cells suggest an important role of purinergic signaling in early embryogenesis, especially in cell proliferation, migration, and differentiation, with different subtypes of receptors participating in these processes. Our understanding of the biological functions of specific P2 receptor subtypes during CNS development and in the adult brain has increased due to the availability of knockout animals and specific inhibition of gene expression or activity of purinergic receptor subtypes. The importance of P2 receptor signaling in neuroprotection, neuroimmunity, and guiding neuronal differentiation, especially in glial and microglial cells, has been related to purinergic receptor expression. Most importantly, specific agonists and antagonists for individual P2 receptor subtypes are both needed for studying their involvement in biological processes. The discovery of such selective compounds will elucidate yet unknown biological functions of P2 receptor subtypes as well as open new avenues for therapeutic approaches to disease states in which purinergic receptor activity is involved.