P2X7 receptor: an emerging target in central nervous system diseases.

The ATP-sensitive homomeric P2X7 receptor (P2X7R) has received particular attention as a potential drug target because of its widespread involvement in inflammatory diseases as a key regulatory element of the inflammasome complex. However, it has only recently become evident that P2X7Rs also play a pivotal role in central nervous system (CNS) pathology. There is an explosion of data indicating that genetic deletion and pharmacological blockade of P2X7Rs alter responsiveness in animal models of neurological disorders, such as stroke, neurotrauma, epilepsy, neuropathic pain, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease, and Huntington's disease. Moreover, recent studies suggest that P2X7Rs regulate the pathophysiology of psychiatric disorders, including mood disorders, implicating P2X7Rs as drug targets in a variety of CNS pathology

The Role of Extracellular Adenosine in Chemical Neurotransmission in the Hippocampus and Basal Ganglia: Pharmacological and Clinical Aspects

Now there is general agreement that the purine nucleoside adenosine is an important neuromodulator in the central nervous system, playing a crucial role in neuronal excitability and synaptic/non-synaptic transmission in the hippocampus and basal ganglia. Adenosine is derived from the breakdown of extra- or intracellular ATP and is released upon a variety of physiological and pathological stimuli from neuronal and non-neuronal sources, i.e. from glial cells and exerts effects diffusing far away from release sites. The resultant elevation of adenosine levels in the extracellular space reaches micromolar level, and leads to the activation A1, A2A, A2B and A3 receptors, localized to pre- and postsynaptic as well as extrasynaptic sites. Activation of presynaptic A1 receptors inhibits the release of the majority of transmitters including glutamate, acetylcholine, noradrenaline, 5-HT and dopamine, whilst the stimulation of A2A receptors facilitates the release of glutamate and acetylcholine and inhibits the release of GABA. These actions underlie modulation of neuronal excitability, synaptic plasticity and coordination of neural networks and provide intriguing target sites for pharmacological intervention in ischemia and Parkinson’s disease. However, despite that adenosine is also released during ischemia, A1 adenosine receptors do not participate in the modulation of excitotoxic glutamate release, which is nonsynaptic and is due to the reverse operation of transporters. Instead, extrasynaptic A1 receptors might be responsible for the neuroprotection afforded by A1 receptor activation

P2 receptor-mediated signaling in the physiological and pathological brain: From development to aging and disease

The purinergic pathway mediates both pro-inflammatory and anti-inflammatory responses, whereas the breakdown of adenosine triphosphate (ATP) is in a critical equilibrium. Under physiological conditions, extracellular ATP is maintained at a nanomolar concentration. Whether released into the medium following tissue damage, inflammation, or hypoxia, ATP is considered a clear indicator of cell damage and a marker of pathological conditions. In this overview, we provide an update on the participation of P2 receptor-mediated purinergic signaling in normal and pathological brain development, with special emphasis on neurodevelopmental psychiatric disorders. Since purinergic signaling is ubiquitous, it is not surprising that it plays a prominent role in developmental processes and pathological alterations. The main aim of this review is to conceptualize the time-dependent dynamic changes in the participation of different players in the purinome in shaping the normal and aberrant developmental patterns and diseases of the central nervous system over one's lifespan

Purinerg receptorok által közvetített hatások komplex vizsgálata: új neuroprotektív terápiás lehetőségek elméleti alapjai = Complex studies on purinergic receptor-mediated actions: a theoretical basis for neuroprotection

Vizsgálataink fő célja a neurotranszmitter felszabadulást serkentő P2 nukleotid receptorok szerepének tisztázása volt fiziológiás és patológiás állapotokban. Feltérképeztük a P2X7 receptort kódoló mRNS eloszlását a központi idegrendszer számos területén. Elsőként azonosítottunk a GABA és glutamát felszabadulás szabályozásában résztvevő, serkentő P2X7 receptorokat a hippokampuszban. Feltártuk a P2X7 receptorok celluláris és szubcelluláris eloszlását ezen agyterületen, igazoltuk a P2X7 receptor részvételét az ATP GABA és glutamát felszabadító hatásában farmakológiai analízis, valamint transzgenikus technológia igénybevételével. Neurokémiai és elektrofizológiai módszerekkel igazoltuk, hogy a P2X7 receptorok funkcionális válaszkészsége fokozódik energiadepriváció hatására. Kimutattuk, hogy a noradrenalin felszabadulást a hippokampuszban serkentő P2X1 és/vagy P2X3 receptorok szabályozzák. Megállapítottuk, hogy az ATP és egyéb purinok képesek önerősítő módon saját felszabadulásukat fokozni a homo- illetve heteroexchange által. Tisztáztuk a mitokondriális inhibitorok és az oxidatív stressz szupraadditív kölcsönhatását a noradrenalin/dopamin felszabadulás kiváltásában a hippokampuszban, illetve a rotenon indukált Parkinson modellben. Feltártuk az IL-1béta purin felszabadulást előidéző hatását. Eredményeink alátámasztották a pályázatban felállított hipotézist, mely szerint a P2X7 vagy egyéb P2X receptorok befolyásolása ígéretes terápiás célpont lehet neurodegeneratív betegségekben. | The main objective of the studies was to identify the role of the facilitatory P2 nucleotide receptors under physiological and pathological conditions. We explored the mRNA expression of P2X7 receptors in several areas of the CNS. We demonstrated for the first time that the activation of P2X7 receptors facilitate the release of GABA and glutamate in the hippocampus, and the cell-type specific distribution of this receptor was also explored. The involvement of P2X7 receptor in the GABA and glutamate releasing effect of ATP was proved by pharmacological analysis and by the utilization of transgenic technology. We also demonstrated by electrophysiological and neurochemical techniques that the functional responsiveness of P2X7 receptors is increased during energy deprivation. On the other hand, the release of noradrenaline is subject to facilitation by P2X1 and /or P2X3 receptors. We identified the homo-and heteroexchange, as a new mechanism, whereby purines could promote the release of each other and themselves. We revealed the supraadditive impact of mitochondrial inhibitors and oxidative stress on noradrenaline release in the hippocampus and on dopamine release in the rotenon induced Parkinson model. In addition the effect of IL-1beta on the release of purines from the hippocampus was also described. In conclusion our findings support our initial hypothesis that P2X7 or other P2X receptors could be attractive therapeutic targets in neurodegenerative diseases

Lack of neuroprotection in the absence of P2X7 receptors in toxin-induced animal models of Parkinson's disease

<p>Abstract</p> <p>Background</p> <p>Previous studies indicate a role of P2X₇receptors in processes that lead to neuronal death. The main objective of our study was to examine whether genetic deletion or pharmacological blockade of P2X₇receptors influenced dopaminergic cell death in various models of Parkinson's disease (PD).</p> <p>Results</p> <p>mRNA encoding P2X₇and P2X₄receptors was up-regulated after treatment of PC12 cells with 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP). P2X₇antagonists protected against MPTP and rotenone induced toxicity in the LDH assay, but failed to protect after rotenone treatment in the MTT assay in PC12 cells and in primary midbrain culture. <it>In vivo </it>MPTP and <it>in vitro </it>rotenone pretreatments increased the mRNA expression of P2X₇receptors in the striatum and substantia nigra of wild-type mice. Basal mRNA expression of P2X₄receptors was higher in P2X₇knockout mice and was further up-regulated by MPTP treatment. Genetic deletion or pharmacological inhibition of P2X₇receptors did not change survival rate or depletion of striatal endogenous dopamine (DA) content after <it>in vivo </it>MPTP or <it>in vitro </it>rotenone treatment. However, depletion of norepinephrine was significant after MPTP treatment only in P2X₇knockout mice. The basal ATP content was higher in the substantia nigra of wild-type mice, but the ADP level was lower. Rotenone treatment elicited a similar reduction in ATP content in the substantia nigra of both genotypes, whereas reduction of ATP was more pronounced after rotenone treatment in striatal slices of P2X₇deficient mice. Although the endogenous amino acid content remained unchanged, the level of the endocannabinoid, 2-AG, was elevated by rotenone in the striatum of wild-type mice, an effect that was absent in mice deficient in P2X₇receptors.</p> <p>Conclusions</p> <p>We conclude that P2X₇receptor deficiency or inhibition does not support the survival of dopaminergic neurons in an <it>in vivo </it>or <it>in vitro </it>models of PD.</p

Purinergic mechanisms in neuroinflammation: An update from molecules to behavior.

The principle functions of neuroinflammation are to limit tissue damage and promote tissue repair in response to pathogens or injury. While neuroinflammation has utility, pathophysiological inflammatory responses, to some extent, underlie almost all neuropathology. Understanding the mechanisms that control the three stages of inflammation (initiation, propagation and resolution) is therefore of critical importance for developing treatments for diseases of the central nervous system. The purinergic signaling system, involving adenosine, ATP and other purines, plus a host of P1 and P2 receptor subtypes, controls inflammatory responses in complex ways. Activation of the inflammasome, leading to release of pro-inflammatory cytokines, activation and migration of microglia and altered astroglial function are key regulators of the neuroinflammatory response. Here, we review the role of P1 and P2 receptors in mediating these processes and examine their contribution to disorders of the nervous system. Firstly, we give an overview of the concept of neuroinflammation. We then discuss the contribution of P2X, P2Y and P1 receptors to the underlying processes, including a discussion of cross-talk between these different pathways. Finally, we give an overview of the current understanding of purinergic contributions to neuroinflammation in the context of specific disorders of the central nervous system, with special emphasis on neuropsychiatric disorders, characterized by chronic low grade inflammation or maternal inflammation. An understanding of the important purinergic contribution to neuroinflammation underlying neuropathology is likely to be a necessary step towards the development of effective interventions

Roles Played by the Na+/Ca2+ Exchanger and Hypothermia in the Prevention of Ischemia-Induced Carrier-Mediated Efflux of Catecholamines into the Extracellular Space: Implications for Stroke Therapy

The release of [3H]dopamine ([3H]DA) and [3H]noradrenaline ([3H]NA) in acutely perfused rat striatal and cortical slice preparations was measured at 37 °C and 17 °C under ischemic conditions. The ischemia was simulated by the removal of oxygen and glucose from the Krebs solution. At 37 °C, resting release rates in response to ischemia were increased; in contrast, at 17 °C, resting release rates were significantly reduced, or resting release was completely prevented. The removal of extracellular Ca2+ further increased the release rates of [3H]DA and [3H]NA induced by ischemic conditions. This finding indicated that the Na+/Ca2+ exchanger (NCX), working in reverse in the absence of extracellular Ca2+, fails to trigger the influx of Ca2+ in exchange for Na+ and fails to counteract ischemia by further increasing the intracellular Na+ concentration ([Na+]i). KB-R7943, an inhibitor of NCX, significantly reduced the cytoplasmic resting release rate of catecholamines under ischemic conditions and under conditions where Ca2+ was removed. Hypothermia inhibited the excessive release of [3H]DA in response to ischemia, even in the absence of Ca2+. These findings further indicate that the NCX plays an important role in maintaining a high [Na+]i, a condition that may lead to the reversal of monoamine transporter functions; this effect consequently leads to the excessive cytoplasmic tonic release of monoamines and the reversal of the NCX. Using HPLC combined with scintillation spectrometry, hypothermia, which enhances the stimulation-evoked release of DA, was found to inhibit the efflux of toxic DA metabolites, such as 3,4-dihydroxyphenylacetaldehyde (DOPAL). In slices prepared from human cortical brain tissue removed during elective neurosurgery, the uptake and release values for [3H]NA did not differ from those measured at 37 °C in slices that were previously maintained under hypoxic conditions at 8 °C for 20 h. This result indicates that hypothermia preserves the functions of the transport and release mechanisms, even under hypoxic conditions. Oxidative stress (H2O2), a mediator of ischemic brain injury enhanced the striatal resting release of [3H]DA and its toxic metabolites (DOPAL, quinone). The study supports our earlier findings that during ischemia transmitters are released from the cytoplasm. In addition, the major findings of this study that hypothermia of brain slice preparations prevents the extracellular calcium concentration ([Ca2+]o)-independent non-vesicular transmitter release induced by ischemic insults, inhibiting Na+/Cl--dependent membrane transport of monoamines and their toxic metabolites into the extracellular space, where they can exert toxic effects