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The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the ionotropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R is known to regulate crucial aspects of neuronal cell biology, including axonal elongation, path-finding, synapse formation and neuroprotection. Moreover, P2X7R modulates neuroinflammation and is posed as a therapeutic target in inflammatory, oncogenic and degenerative disorders. However, the lack of reliable technical and pharmacological approaches to detect this receptor represents a major hurdle in its study. Here, we took advantage of the P2rx7-EGFP reporter mouse, which expresses enhanced green fluorescence protein (EGFP) immediately downstream of the P2rx7 proximal promoter, to conduct a detailed study of its distribution. We performed a comprehensive analysis of the pattern of P2X7R expression in the brain of E18.5 mouse embryos revealing interesting areas within the CNS. Particularly, strong labelling was found in the septum, as well as along the entire neural roof plate zone of the brain, except chorioidal roof areas, but including specialized circumventricular roof formations, such as the subfornical and subcommissural organs (SFO; SCO). Moreover, our results reveal what seems a novel circumventricular organ, named by us postarcuate organ (PArcO). Furthermore, this study sheds light on the ongoing debate regarding the specific presence of P2X7R in neurons and may be of interest for the elucidation of additional roles of P2X7R in the idiosyncratic histologic development of the CNS and related systemic functions. ; This work was supported by grants "Red de Excelencia Consolider-Ingenio Spanish Ion Channel Initiative" (BFU2015-70067REDC) from the Ministry of Economy and Competitiveness (BFU2014-53654-P), BRADE-Comunidad de Madrid (S2013/ICE-2958), UCM-Santander (PR26/16-18B-3; PR75/18) and Fundación Ramón Areces Grant program (PR2018/16–02). Maria Benito Leon is recipient of a contract from the "Fondo de Garantía Juvenil, Comunidad de Madrid" CAM PEJD-2016/BMD-2572. Felipe Ortega acknowledges support from the Ramon y Cajal Program of the Spanish Ministry of Economy and Competitiveness (MEC: RYC-2013–13290). This work has been also supported by Comunidad de Madrid, project "S2017/BMD-3867 (RENIM-CM)", co-funded by European Structural and Investment Fund. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015–0505). MVG has been supported by Ministerio de Ciencia, Innovación y Universidades, ISCIII-FIS grants PI18/00462 co-financed by ERDF, European Union (FEDER) Funds from the European Commission, European Union, "A way of making Europe".

The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the ionotropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R is known to regulate crucial aspects of neuronal cell biology, including axonal elongation, path-finding, synapse formation and neuroprotection. Moreover, P2X7R modulates neuroinflammation and is posed as a therapeutic target in inflammatory, oncogenic and degenerative disorders. However, the lack of reliable technical and pharmacological approaches to detect this receptor represents a major hurdle in its study. Here, we took advantage of the P2rx7-EGFP reporter mouse, which expresses enhanced green fluorescence protein (EGFP) immediately downstream of the P2rx7 proximal promoter, to conduct a detailed study of its distribution. We performed a comprehensive analysis of the pattern of P2X7R expression in the brain of E18.5 mouse embryos revealing interesting areas within the CNS. Particularly, strong labelling was found in the septum, as well as along the entire neural roof plate zone of the brain, except chorioidal roof areas, but including specialized circumventricular roof formations, such as the subfornical and subcommissural organs (SFO; SCO). Moreover, our results reveal what seems a novel circumventricular organ, named by us postarcuate organ (PArcO). Furthermore, this study sheds light on the ongoing debate regarding the specific presence of P2X7R in neurons and may be of interest for the elucidation of additional roles of P2X7R in the idiosyncratic histologic development of the CNS and related systemic functions. ; This work was supported by grants "Red de Excelencia Consolider-Ingenio Spanish Ion Channel Initiative" (BFU2015-70067REDC) from the Ministry of Economy and Competitiveness (BFU2014-53654-P), BRADE-Comunidad de Madrid (S2013/ICE-2958), UCM-Santander (PR26/16-18B-3; PR75/18) and Fundación Ramón Areces Grant program (PR2018/16–02). Maria Benito Leon is recipient of a contract from the "Fondo de Garantía Juvenil, Comunidad de Madrid" CAM PEJD-2016/BMD-2572. Felipe Ortega acknowledges support from the Ramon y Cajal Program of the Spanish Ministry of Economy and Competitiveness (MEC: RYC-2013–13290). This work has been also supported by Comunidad de Madrid, project "S2017/BMD-3867 (RENIM-CM)", co-funded by European Structural and Investment Fund. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015–0505). MVG has been supported by Ministerio de Ciencia, Innovación y Universidades, ISCIII-FIS grants PI18/00462 co-financed by ERDF, European Union (FEDER) Funds from the European Commission, European Union, "A way of making Europe". ; Sí

The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the ionotropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R is known to regulate crucial aspects of neuronal cell biology, including axonal elongation, path-finding, synapse formation and neuroprotection. Moreover, P2X7R modulates neuroinflammation and is posed as a therapeutic target in inflammatory, oncogenic and degenerative disorders. However, the lack of reliable technical and pharmacological approaches to detect this receptor represents a major hurdle in its study. Here, we took advantage of the P2rx7-EGFP reporter mouse, which expresses enhanced green fluorescence protein (EGFP) immediately downstream of the P2rx7 proximal promoter, to conduct a detailed study of its distribution. We performed a comprehensive analysis of the pattern of P2X7R expression in the brain of E18.5 mouse embryos revealing interesting areas within the CNS. Particularly, strong labelling was found in the septum, as well as along the entire neural roof plate zone of the brain, except chorioidal roof areas, but including specialized circumventricular roof formations, such as the subfornical and subcommissural organs (SFO; SCO). Moreover, our results reveal what seems a novel circumventricular organ, named by us postarcuate organ (PArcO). Furthermore, this study sheds light on the ongoing debate regarding the specific presence of P2X7R in neurons and may be of interest for the elucidation of additional roles of P2X7R in the idiosyncratic histologic development of the CNS and related systemic functions. ; We thank Dr C. Ofderoad for his critical comments. This work was supported by grants "Red de Excelencia Consolider-Ingenio Spanish Ion Channel Initiative" (BFU2015-70067REDC) from the Ministry of Economy and Competitiveness (BFU2014-53654-P), BRADE-Comunidad de Madrid (S2013/ICE-2958), UCM-Santander (PR26/16-18B-3; PR75/18) and Fundación Ramón Areces Grant program (PR2018/16–02). Maria Benito Leon is recipient of a contract from the "Fondo de Garantía Juvenil, Comunidad de Madrid" CAM PEJD-2016/BMD-2572. Felipe Ortega acknowledges support from the Ramon y Cajal Program of the Spanish Ministry of Economy and Competitiveness (MEC: RYC-2013–13290). This work has been also supported by Comunidad de Madrid, project "S2017/BMD-3867 (RENIM-CM)", co-funded by European Structural and Investment Fund. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015–0505). MVG has been supported by Ministerio de Ciencia, Innovación y Universidades, ISCIII-FIS grants PI18/00462 co-financed by ERDF, European Union (FEDER) Funds from the European Commission, European Union, "A way of making Europe".

Downstream Regulatory Element Antagonist Modulator (DREAM)/KChIP3/calsenilin is a neuronal calcium sensor (NCS) with multiple functions, including the regulation of A-type outward potassium currents (I A). This effect is mediated by the interaction between DREAM and KV4 potassium channels and it has been shown that small molecules that bind to DREAM modify channel function. A-type outward potassium current (I A) is responsible of the fast repolarization of neuron action potentials and frequency of firing. Using surface plasmon resonance (SPR) assays and electrophysiological recordings of KV4.3/DREAM channels, we have identified IQM-266 as a DREAM ligand. IQM-266 inhibited the KV4.3/DREAM current in a concentration-, voltage-, and time-dependent-manner. By decreasing the peak current and slowing the inactivation kinetics, IQM-266 led to an increase in the transmembrane charge ( QKV4.3/DREAM ) at a certain range of concentrations. The slowing of the recovery process and the increase of the inactivation from the closed-state inactivation degree are consistent with a preferential binding of IQM-266 to a pre-activated closed state of KV4.3/DREAM channels. Finally, in rat dorsal root ganglion neurons, IQM-266 inhibited the peak amplitude and slowed the inactivation of I A. Overall, the results presented here identify IQM-266 as a new chemical tool that might allow a better understanding of DREAM physiological role as well as modulation of neuronal I A in pathological processes. ; PC was the recipient of a postgraduate FPI fellowship from the Spanish Ministry of Economy, Industry and Competitivity (MINECO). This work was funded by the Spanish Ministry of Economy, Industry and Competitivity (Ministerio de Economía y Competitividad; AEI-FEDER, EU grants): SAF2012-32209 and BFU2015-67284-R (to MG-R), SAF2014-53412-R and SAF2017- 89554-R (to JN), SAF2013-45800-R, SAF2016-75021-R (to CV) and SAF2015-66275-C2-2-R (to MM-M); Universidad Complutense de Madrid (UCM) grant: PR75/18-21593 (to AA); the Instituto de Salud Carlos III CIBERNED and CIBERCV programs (to JN and to CV, respectively) and the Madrid regional government/Neurodegmodels (to JN); Consejo Superior de Investigaciones Científicas (CSIC) grants: PIE 201820E104 (to CV) and 201880E109 (to MG-R and MM-M). ; We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

Prolonged seizures (status epilepticus, SE) may drive hippocampal dysfunction and epileptogenesis, at least partly, through an elevation in neurogenesis, dysregulation of migration and aberrant dendritic arborization of newly-formed neurons. MicroRNA-22 was recently found to protect against the development of epileptic foci, but the mechanisms remain incompletely understood. Here, we investigated the contribution of microRNA-22 to SE-induced aberrant adult neurogenesis. SE was induced by intraamygdala microinjection of kainic acid (KA) to model unilateral hippocampal neuropathology in mice. MicroRNA-22 expression was suppressed using specific oligonucleotide inhibitors (antagomir-22) and newly-formed neurons were visualized using the thymidine analog iodo-deoxyuridine (IdU) and a green fluorescent protein (GFP)-expressing retrovirus to visualize the dendritic tree and synaptic spines. Using this approach, we quantified differences in the rate of neurogenesis and migration, the structure of the apical dendritic tree and density and morphology of dendritic spines in newly-formed neurons.SE resulted in an increased rate of hippocampal neurogenesis, including within the undamaged contralateral dentate gyrus (DG). Newly-formed neurons underwent aberrant migration, both within the granule cell layer and into ectopic sites. Inhibition of microRNA-22 exacerbated these changes. The dendritic diameter and the density and average volume of dendritic spines were unaffected by SE, but these parameters were all elevated in mice in which microRNA-22 was suppressed. MicroRNA-22 inhibition also reduced the length and complexity of the dendritic tree, independently of SE. These data indicate that microRNA-22 is an important regulator of morphogenesis of newly-formed neurons in adults and plays a role in supressing aberrant neurogenesis associated with SE ; This work was supported by funding from Science Foundation Ireland (13/SIRG/2098, 17/CDA/4708 and 16/TIDA/4059 to TE, 13/SIRG/2114 to EJ-M, 17/TIDA/5002 to CR, 13/IA/1891 and 16/RC/3948 to DH and co-funded under the European Regional Development Fund and by FutureNeuro Industry partners) from the Health Research Board (HRA-POR-2015-1243 to TE), from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement n◦ 602130 (to DH), from the H2020 Marie Skłowdowksa-Curie Actions Individual Fellowship (753527 to EB), from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement (No 766124 to TE), S2013/ICE-2958 from Comunidad de Madrid to MM-P, from Fundación ''La Caixa'' to JM-R and from Areces Foundation C-XVIII and the Minister of Science and Universities of Spain BFU2014-53654-P to MM-P