GABAB receptor-mediated presynaptic potentiation of ATP ionotropic receptors in rat midbrain synaptosomes

Chemical Stimulation of Rodent and Human Cortical Synaptosomes: Implications in Neurodegeneration

Synaptic plasticity events, including long-term potentiation (LTP), are often regarded as correlates of brain functions of memory and cognition. One of the central players in these plasticity-related phenomena is the α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR). Increased levels of AMPARs on postsynaptic membranes thus constitute a biochemical measure of LTP. Isolated synaptic terminals (synaptosomes) are an excellent ex vivo tool to monitor synaptic physiology in healthy and diseased brains, particularly in human research. We herein describe three protocols for chemically-induced LTP (cLTP) in synaptosomes from both rodent and human brain tissues. Two of these chemical stimulation protocols are described for the first time in synaptosomes. A pharmacological block of synaptosomal actin dynamics confirmed the efficiency of the cLTP protocols. Furthermore, the study prototypically evaluated the deficiency of cLTP in cortical synaptosomes obtained from human cases of early-onset Alzheimer’s disease (EOAD) and frontotemporal lobar degeneration (FLTD), as well as an animal model that mimics FLTD.

Geoffrey Burnstock, our friend and magister: the diadenosine polyphosphate connection

Development of science needs the cooperation of many creative brains. Sometimes, ideas on a specific area get suddenly exhausted and then it is the time for a privileged mind to think in a different way and reach the turning point to introduce a new paradigm. This happened to Geoffrey Burnstock, a heterodox thinker and nonconformist scientist that has been the paladin of purinergic signalling since 1972, opening neuroscience to the understanding of organs and tissues functioning and development of a new pharmacology. This review summarizes the contribution of our group to the understanding of the role of the diadenosine polyphosphates, Ap_nA, as signalling molecules, describing their tissue and organ distribution, their transport and storage in secretory vesicles and their release and interaction with purinergic receptors. We also have to acknowledge the friendly and kindly support of Professor Burnstock that showed a great interest in the field from our initial findings and actively stimulated our efforts to establish the extracellular roles and biological significance of these dinucleotides.

The Neurotoxic Role of Extracellular Tau Protein

Tauopathies are a class of neurodegenerative diseases associated with the microtubule-associated protein tau, with Alzheimer’s disease (AD) being the most prevalent related disorder. Neurofibrillary tangles (NFTs) are one of the neuropathological hallmarks present in the brains of AD patients. Because NFTs are aberrant intracellular inclusions formed by hyperphosphorylated tau, it was initially proposed that phosphorylated and/or aggregated intracellular tau protein was causative of neuronal death. However, recent studies suggest a toxic role for non-phosphorylated and non-aggregated tau when it is located in the brain extracellular space. In this work, we will discuss the neurotoxic role of extracellular tau as well its involvement in the spreading of tau pathologies.

TNAP Plays a Key Role in Neural Differentiation as well as in Neurodegenerative Disorders

New evidences have been reported that point to the ecto-enzyme, tissue-nonspecific alkaline phosphatase (TNAP), as a key element at the origin of two opposite phenomena, neuronal differentiation and neuronal degeneration. During brain development, TNAP plays an essential role for establishing neuronal circuits. The pro-neuritic effect induced by TNAP, which results in axonal length increase, is due to its enzymatic hydrolysis of extracellular ATP at the surrounding area of the axonal growth cone . In this way, the activation of P2X7 receptor is prevented and as a consequence there is no inhibition of axonal growth. The existence of a close functional interrelation between both purinergic elements is finally supported by the fact that both elements may control, in a reciprocal way, the expression level of the other. On the opposite stage, recent evidences indicate that TNAP plays a key role in spreading the neurotoxicity effect induced by extracellular hyperphosphorylated tau protein, the main component of intracellular neurofibrillary tangles present in the brain of Alzheimer disease patients. TNAP exhibits a broad substrate specificity and in addition to nucleotides it is able to dephosphorylate extracellular proteins, such as the hyperphosphorylated tau protein once it is released to the extracellular medium. Dephosphorylated tau protein behaves as an agonist of muscarinic M1 and M3 receptors, provoking a robust and sustained intracellular calcium increase that finally triggering neuronal death. Besides, activation of muscarinic receptors by dephosphorylated tau increases the expression of TNAP, which could explain the increase in TNAP activity and protein levels detected in Alzheimer disease.

Tissue-nonspecific Alkaline Phosphatase Regulates Purinergic Transmission in the Central Nervous System During Development and Disease

Tissue-nonspecific alkaline phosphatase (TNAP) is one of the four isozymes in humans and mice that have the capacity to hydrolyze phosphate groups from a wide spectrum of physiological substrates. Among these, TNAP degrades substrates implicated in neurotransmission. Transgenic mice lacking TNAP activity display the characteristic skeletal and dental phenotype of infantile hypophosphatasia, as well as spontaneous epileptic seizures and die around 10 days after birth. This physiopathology, linked to the expression pattern of TNAP in the central nervous system (CNS) during embryonic stages, suggests an important role for TNAP in neuronal development and synaptic function, situating it as a good target to be explored for the treatment of neurological diseases. In this review, we will focus mainly on the role that TNAP plays as an ectonucleotidase in CNS regulating the levels of extracellular ATP and consequently purinergic signaling.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

The co-treatments of vigabatrin and P2X receptor antagonists protect ischemic neuronal cell death in the gerbil hippocampus

During transient global ischemia, the excessive accumulation of intracellular Ca2+ induced by several episodes triggers delayed neuronal death within the vulnerable CA1 region of the hippocampus after ischemia-reperfusion insults. Although P2X receptors provide an additional source of Ca2+ entry, little data are available that these receptors could modulate the performance of the ischemic neuronal death. Therefore, we investigated the roles of the P2X receptor in the ischemic neuronal damage associated with various sequelae of transient ischemia, and the effects of their antagonist on the ischemic insults. As the results, ischemic insults increased P2X receptor expression in the gerbil hippocampus. Neither vigabatrin (VGB) nor P2X receptor antagonists (suramin, pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid) protected against the delayed neuronal death in the CA1 region of the hippocampus after ischemia. However, the co-treatments of VGB and P2X receptor antagonists effectively prevent ischemia-induced neurodegeneration. Therefore, these findings suggest that blockade of the P2X receptor accompanied by activation of GABAergic inhibition may play an important role in the neuroprotection against ischemic insults.

P2 receptor web: Complexity and fine-tuning

The present review offers a new perspective on a family of receptors, termed P2 receptors, specific for nucleoside tri- and diphosphates of purines/pyrimidines. We emphasize here that while decoding the inputs of various related extracellular ligands, P2 receptors are a clear example of increasing biological complexity. They are represented by 7 ionotropic P2X and 8 metabotropic P2Y receptors; they have very heterogeneous ligands and binding characteristics, molecular properties, transduction mechanisms, cellular localization and protein-protein interactions. While the reason for this sophistication is unknown, a few compelling issues emerge while looking at such a rich variety. We ask, for instance, why so many different receptor subtypes are necessary for triggering biological properties and functions, and if these receptors are more than the sum of their single entities. A first possibility is that newly synthesized P2 proteins are casually located on the cell surface (stochastic hypothesis). Alternatively, distinct subunits are engaged on different cell phenotypes by genetic control (genetic determinism) and/or selective recruitment under physiopathological conditions and epigenetic stimuli (epigenetic determinism). Nevertheless, an appropriate way to both dissect the vast biological scenario and molecular complexity among P2 receptors and to integrate and upgrade their assortment is to regard them as a "combinatorial receptor web", that is, a dynamic architecture of P2 proteins demonstrating economic efficiency and involving a process of "fine-tuning", a mechanism which endorses the dynamic nature of all biological reactions. In the present analysis, we stimulate a scientific query about what contributes to such a vast P2 receptor sophistication.

P2Y1and P2X7receptors induce calcium/calmodulin-dependent protein kinase II phosphorylation in cerebellar granule neurons

The activation of nucleotide receptors-- both ionotropic, P2X, and most of metabotropic, P2Y-- increases intracellular calcium concentration, resulting in calcium/calmodulin-dependent protein kinase II (CaMKII) activation. Stimulation of cerebellar granule neurons in culture-- with different P2X and P2Y agonists and their effect on CaMKII phosphorylation-- was studied using immunocytochemical and microfluorimetrical techniques. P2X agonist: 2'-3'-o-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-meATP) and diadenosine pentaphosphate (Ap(5)A); and P2Y agonists: 2-(methylthyo)-adenosine diphosphate (2MeSADP) and uridine 5'-bisphosphate (UDP); tested induced a CaMKII phosphorylation but with a different immunostaining pattern in each group. Stimulation with 2MeSADP induced a Ca(2+) release from intracellular stores and a significant CaMKII phosphorylation in cell somas and neurites. This agrees with the subcellular distribution of P2Y(1). MRS 2179, a specific P2Y(1) inhibitor, antagonized the 2MeSADP effect. On the other hand, cerebellar granule neuron stimulation with BzATP, in Mg(2+)-free conditions, produced extracellular calcium entrance and, as a result, a significant increase in CaMKII phosphorylation mostly in fibres, which correspond with P2X(7) subdistribution. Immunocytochemical and microfluorimetrical experiments, using Zn(2+) and Brilliant Blue G (BBG), as a specific P2X(7) antagonist, confirmed that BzATP was acting through the P2X(7) receptor. These results indicate that P2Y(1) and P2X(7) produce a significant increase in CaMKII phosphorylation, but show important differences in subcellular distribution and in effect duration. P2X(7) activation in granule neurons is not associated with pore formation, according to the absence of YO-PRO-1 fluorescence. The abundant presence of P2X(7) at the synaptic structures suggests a relevant role played by this receptor in synaptic plasticity.

Presence of diverse functional P2X receptors in rat cerebellar synaptic terminals

Studies in individual synaptic terminals have demonstrated the presence of diverse functional P2X receptors in rat cerebellum. No immunolabelling for P2X1, P2X4, P2X5 and P2X6, and scarce presence of P2X2 were found at the cerebellar synaptic terminals. P2X3 immunolabelling was present in 28% of isolated synaptosomes. At these synaptic terminals, nucleotides as ATP or alpha,beta-meATP induced Ca2+ transients in the presence of extracellular Ca2+, showing homologous and heterologous receptor desensitization in 60% of cases. Ip5I 10 nM did not block responses to alpha,beta-meATP, but inhibition occurred when antagonist concentrations were equal or higher than 100 nM. These data agree with the presence of abundant P2X3 homomeric receptors. P2X7 immunolabelling was present in 60% of terminals and P2X7 receptor hallmarks in Ca2+ responses have been found. BzATP was more potent than ATP and responses were potentiated when assayed in Mg2+-free medium. EC50 values were, respectively, 39.4+/-0.4 and 0.3+/-0.1 microM for ATP in the presence or absence of Mg2+. Maximal values of synaptosomal calcium transients, in the presence or absence of Mg2+, were, respectively, 91.6+/-11.9 and 132.9+/-12.9 nM for ATP; and 104.3+/-9.4 and 169.7+/-17.1 nM for BzATP. In addition, Zn2+ inhibited ATP responses in the absence of Mg2+ and the P2X7 specific antagonist Brilliant Blue G completely blocked these responses in one half of synaptosomes. This study reports the presence of functional P2X3 and P2X7 receptors at synaptic sites, which provides complexity and regulatory possibilities to the cerebellar neurotransmission.

Molecular physiology of P2 receptors in the central nervous system

Neurons of the central nervous system (CNS) are endowed with ATP-sensitive receptors belonging to the P2X (ligand-gated cationic channels) and P2Y (G protein-coupled receptors) types. Whereas a number of P2X receptors mediate fast synaptic responses to the transmitter ATP, P2Y receptors mediate either slow changes of the membrane potential in response to non-synaptically released ATP or the interaction with receptors for other transmitters. To date seven P2X and seven P2Y receptors of human origin have been molecularly identified and functionally characterized. P2X subunits may occur as homooligomers or as heterooligomeric assemblies of more than one subunit. P2X(7) subunits do not form heterooligomeric assemblies and are unique in mediating apoptosis and necrosis of glial cells and possibly also of neurons. The P2X(2), P2X(4), P2X(4)/P2X(6) and P2Y(1) receptors appear to be the predominant neuronal types. The localisation of these receptors may be at the somato-dendritic region (postsynaptic) or at the nerve terminals (presynaptic). Postsynaptic P2 receptors appear to be mostly excitatory, while presynaptic P2 receptors may be either excitatory (P2X) or inhibitory (P2Y). Since in the CNS the stimulation of a single neuron may activate multiple networks, a concomitant stimulation of facilitatory and inhibitory circuits as a result of ATP release is also possible. Finally, the enzymatic degradation of ATP may lead to the local generation of adenosine which can modulate via A(1) or A(2A) receptor-activation the ATP effect.

Molecular structure and physiological functions of GABA(B) receptors

GABA(B) receptors are broadly expressed in the nervous system and have been implicated in a wide variety of neurological and psychiatric disorders. The cloning of the first GABA(B) receptor cDNAs in 1997 revived interest in these receptors and their potential as therapeutic targets. With the availability of molecular tools, rapid progress was made in our understanding of the GABA(B) system. This led to the surprising discovery that GABA(B) receptors need to assemble from distinct subunits to function and provided exciting new insights into the structure of G protein-coupled receptors (GPCRs) in general. As a consequence of this discovery, it is now widely accepted that GPCRs can exist as heterodimers. The cloning of GABA(B) receptors allowed some important questions in the field to be answered. It is now clear that molecular studies do not support the existence of pharmacologically distinct GABA(B) receptors, as predicted by work on native receptors. Advances were also made in clarifying the relationship between GABA(B) receptors and the receptors for gamma-hydroxybutyrate, an emerging drug of abuse. There are now the first indications linking GABA(B) receptor polymorphisms to epilepsy. Significantly, the cloning of GABA(B) receptors enabled identification of the first allosteric GABA(B) receptor compounds, which is expected to broaden the spectrum of therapeutic applications. Here we review current concepts on the molecular composition and function of GABA(B) receptors and discuss ongoing drug-discovery efforts.

Interaction between dinucleotide and nicotinic receptors in individual cholinergic terminals

Functional ionotropic nucleotidic receptors responding to diadenosine pentaphospate and nicotinic receptors responding to epibatidine coexpress in 19% of the total rat midbrain cholinergic terminals, as determined by the combination of immunological and microfluorimetric techniques. Activation of each independent receptor induces the intrasynaptosomal [Ca2+]i and acetylcholine (ACh) release in a dose-dependent way. The responses are inhibited by antagonists of the dinucleotide receptor and nicotinic receptors, thus confirming the involvement of specific receptors in both functions. Stimulation of single cholinergic terminal with both agonists altogether results in a significant decrease of the [Ca2+]i signaling compared with responses of each independent agonist. Inhibitory interaction between both receptors is reverted when one of them is blocked by specific antagonists, both in [Ca2+]i, and subsequent ACh release. The receptor's inhibitory cross talk confirm the involvement of calcium/calmodulin-dependent protein kinase II, CaMKII, as the inhibitory effects are reverted in the presence of the specific inhibitors KN-62 (2-[N-(4'-methoxybenzenesulfonyl)]-amino-N-(4'-chlorophenyl)-2-propenyl-N-methylbenzylamine phosphate) and KN-93 (N-(2-[N-[4-chlorocinnamyl]-N-methylaminomethyl]phenyl)-N-(2-hydroxyethyl)-4-methoxybenzenesulphonamide). These results demonstrate the existence of an efficient interaction between these two channel populations, opening a new understanding of the functioning of the cholinergic synaptic terminals or terminals containing other neurotransmitters but exhibiting these receptor types or ones that are similar.

P2X3receptor localizes into lipid rafts in neuronal cells

P2X receptors are a family of seven (P2X(1-7)) cation channels gated by extracellular ATP, widely expressed in neurons and nonneuronal cells. Lipid rafts are cholesterol/sphingolipid-rich membrane domains, involved in many cellular processes, including transmembrane receptor signaling, vesicle traffic, and protein sorting. We provide direct biochemical evidence that P2X3 receptor localizes into lipid rafts, in primary cultures of cerebellar granule neurons as well as in brain and dorsal root ganglia extracts. We show that P2X3 exhibits all the characteristics distinctive of a protein associated with lipid rafts. These characteristics include resistance to detergent extraction at 4 degrees C, solubility after extraction of cholesterol from membranes with either saponin or methyl-beta-cyclodextrin, and partitioning to low buoyant density fractions after sucrose gradient centrifugation in both detergent-containing and detergent-free conditions. Furthermore, P2X3 localizes in raft-containing fractions in transiently transfected SH-SY5Y neuroblastoma cells. The present finding contributes to the characterization of the functional localization of P2X3 in neurons and provides a novel potential mechanism for correct targeting and dynamic activation of this receptor.

GABA(B) receptor-mediated regulation of P2X7 receptor expression in the gerbil hippocampus

In the present study, the P(2)X(7) receptor expression in the gerbil hippocampus and GABA-mediated responses of its expression was investigated in order to identify the roles of the P(2)X(7) receptor on seizure activity and recovery mechanisms. P(2)X(7) receptor immunoreactivity in seizure-resistant (SR) gerbils was similar to that in pre-seizure group of seizure-sensitive (SS) gerbils. The administration of baclofen, a GABA(B) receptor agonist, P(2)X(7) receptor immunoreactivity was decreased in the mossy fiber, compared with that of non-treated gerbils, whereas treatment with phaclofen, a GABA(B) receptor antagonist, elevated P(2)X(7) receptor expression. Neither the treatments with GABA(A) receptor agonist nor antagonist affected P(2)X(7) receptor expression in the hippocampus. These findings suggest that altered P(2)X(7) receptor expression may not be involved in the epileptogenesis or seizure activity in gerbils, and presynaptic GABA(B) receptor-mediated actions may be closely related with the regulation of P(2)X(7) receptor expression in the gerbil hippocampus.

GABA modulates presynaptic signalling mediated by dinucleotides on rat synaptic terminals

Diadenosine pentaphosphate (Ap(5)A) elicits Ca(2+) transients in isolated rat midbrain synaptic terminals acting through specific ionotropic dinucleotide receptors. The activation of GABA(B) receptors by baclofen changes the sigmoidal concentration-response curve for Ap(5)A (EC(50) = 44 microM) into biphasic curves. Thus, when GABA(B) receptors are activated, the curve shows a high-affinity component in the picomolar range (EC(50) = 77 pM) and a low-affinity component in the micromolar range (EC(50) = 17 microM). In addition, in the presence of GABA or baclofen, Ap(5)A calcium responses are increased up to 50% over the control values. Saclofen, a specific antagonist of GABA(B) receptors, blocks the potentiatory effect of baclofen. As occurs with Ap(5)A, GABA(B) receptors are also capable to modulate diguanosine pentaphosphate (Gp(5)G)-induced calcium responses. The combination of immunocytochemical and microfluorimetric techniques carried out on single synaptic terminals have shown that in the presence of baclofen, 64% of the terminals responding to 100 microM Ap(5)A are also able to respond to 100 nM Ap(5)A. This value is close to the percentage of synaptic terminals responding to Ap(5)A and labeled with the anti-GABA(B) receptor antibody (69%). The activity of cyclic AMP-dependent protein kinase (PKA) seems to be involved in the potentiatory effect of GABA(B) receptors on Ap(5)A calcium responses, because PKA activation by forskolin or dibutiryl cyclic AMP blocks the potentiatory effect of baclofen, whereas PKA inhibition facilitates calcium signaling mediated by Ap(5)A. These results demonstrate that the activation of presynaptic GABA(B) receptors is able to modulate dinucleotide responses in synaptic terminals.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Dehydroepiandrosterone potentiates native ionotropic ATP receptors containing the P2X2 subunit in rat sensory neurones

We have studied the modulatory effect of dehydroepiandrosterone (DHEA), the most abundant neurosteroid produced by glial cells and neurones, on membrane currents induced by the activation of ionotropic ATP (P2X) receptors in neonatal rat dorsal root ganglion neurones. ATP (1 microM) induced three types of currents/responses termed F (fast and transient), S (slowly desensitizing) and M (mixed, sum of F- and S-type responses). DHEA (10 nM to 100 microM) concentration-dependently increased the amplitude of plateau-like currents of S- and M-type responses evoked by submaximal (1 microM) but not saturating (100 microM or 1 mM) concentrations of ATP. Alphabeta-methylene ATP (alphabetame-ATP, 5 microM) also evoked F-, S- and M-type responses, the plateau phases of which were potentiated by lowering external pH (6.3) and by ivermectin (IVM, 3 microM), indicating the presence heteromeric P2X2-containing receptors and possibly of functional native P2X4/6 receptors. There was a strict correlation between the potentiating effects of low pH and DHEA on alphabetame-ATP responses but not between that of IVM and DHEA, suggesting that DHEA selectively modulated P2X2-containing receptors. DHEA also potentiated putative homomeric P2X2 receptor responses recorded in the continuous presence of 1 microM 2'-(or 3')-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP). Our results constitute the first demonstration of a fast potentiation of P2X receptors by a neurosteroid and suggest that DHEA could be an endogenous modulator of P2X2-containing receptors thereby contributing to the facilitation of the detection and/or the transmission of nociceptive messages, particularly under conditions of inflammatory pain where the P2X receptor signalling pathway appears to be upregulated.

Coexpression of functional P2X and P2Y nucleotide receptors in single cerebellar granule cells

The present study describes the presence and expression of functional nucleotide receptors, both ionotropic and metabotropic, in highly purified cultures of cerebellar granule neurons. Microfluorimetric experiments have been carried out to record specific [Ca(2+)](i) transients in individual granule neurons after challenge with diverse nucleotides. Although great heterogeneity was found in nucleotide responses in single cells, these responses all became modified during the course of granule cell differentiation, not only at the level of the number of responding cells, but also in the magnitude of the response to nucleotides. These in vitro developmental changes were more significant in metabotropic responses to pyrimidine nucleotides, UTP and UDP, which were down- and upregulated, respectively, during the time in culture. At least two types of ADP-specific receptors seem expressed in different granule cell subpopulations responding to 2MeSADP, as the specific P2Y(1) antagonist MRS-2179 inhibited Ca(2+) responses in only one of these populations. The great diversity of metabotropic responses observed was confirmed by the RT-PCR expression of different types of P2Y receptors in granule cell cultures: P2Y(1), P2Y(4), P2Y(6), and P2Y(12). Similarly, ionotropic nucleotide responses were confirmed by the presence of specific messengers for different P2X subunits, and by immunolabeling studies (P2X(1), P2X(2), P2X(3), P2X(4) and P2X(7)). Immunolabeling reflected great variety in the P2X subunit distribution along the granule neuron cytoarchitecture, with P2X(2), P2X(3) and P2X(4) present at somatodendritic locations, and P2X(1), P2X(7), and P2X(3), located at the axodendritic prolongations. The punctuated labeling pattern obtained for P2X(3) and P2X(7) subunits is particularly notable, as it presents a high degree of colocalization with synaptophysin, a specific marker of synaptic vesicles, suggesting specialized localization and function in granule neurons.