P2X Receptor Immunoreactivity Research Articles

Chemical phenotypes of P2X2 purinoreceptor immunoreactive cell bodies in the area postrema

Purines such as adenosine 5'-triphosphate (ATP) act as extracellular messengers through specific purinergic receptors. Three different classes of purinergic receptors have been identified and termed P1, P2X, and P2Y. The purinergic receptor subunit P2X2 is a ligand-gated ion channel that is widely expressed by neurons in the CNS. In the brainstem medulla oblongata, the ionotropic P2X2 receptor (P2X2R) is enriched in the area postrema (AP). Two different antisera to P2X2R were used to determine the chemical nature of P2X2R immunoreactive cell bodies in the rat AP, an area lacking a blood-brain barrier. Subcellularly, P2X2R immunoreactivity was located to the periphery of individual cell bodies. The majority of P2X2R-immunoreactive cells were shown to contain tyrosine hydroxylase (TH) (63.5 ± 7.7%) and dopamine β-hydroxylase (61.5 ± 5.1%). Phenylethanolamine N-methyltransferase (PNMT)-containing cells were not detected in the AP, supporting a noradrenergic nature of P2X2R cells in the AP. There were no P2X2R-immunoreactive cells in the AP that contained the GABA-synthesizing enzyme glutamic acid decarboxylase 65. Only single vesicular glutamate transporter 2-immunoreactive cell bodies that were not P2X2R-positive were demonstrated in the AP. Some P2X2R-positive cells in the AP were immunoreactive for the neuropeptides substance P and pituitary adenylate cyclase-activating polypeptide, whereas dynorphin-, enkephalin-, or cholecystokinin-positive cells were not P2X2R-immunoreactive. Presence of P2X2R in a majority of noradrenergic cells of the AP implies that ATP may have a regulatory action on neuronal noradrenaline release from the AP, a circumventricular organ with a strategic position enabling interactions between circulating substances and the central nervous system.

Effects of Ischemia and Reperfusion on P2X2 Receptor Expressing Neurons of the Rat Ileum Enteric Nervous System

We investigated the effects of ischemia/reperfusion in the intestine (I/R-i) on purine receptor P2X2-immunoreactive (IR) neurons of the rat ileum. The superior mesenteric artery was occluded for 45 min with an atraumatic vascular clamp and animals were sacrificed 4 h later. Neurons of the myenteric and submucosal plexuses were evaluated for immunoreactivity against the P2X2 receptor, nitric oxide synthase (NOS), choline acetyl transferase (ChAT), calbindin, and calretinin. Following I/R-i, we observed a decrease in P2X2 receptor immunoreactivity in the cytoplasm and surface membranes of neurons of the myenteric and submucosal plexuses. These studies also revealed an absence of calbindin-positive neurons in the I/R-i group. In addition, the colocalization of the P2X2 receptor with NOS, ChAT, and calretinin immunoreactivity in the myenteric plexus was decreased following I/R-i. Likewise, the colocalization between P2X2 and calretinin in neurons of the submucosal plexus was also reduced. In the I/R-i group, there was a 55.8% decrease in the density of neurons immunoreactive (IR) for the P2X2 receptor, a 26.4% reduction in NOS-IR neuron, a 25% reduction in ChAT-IR neuron, and a 47% reduction in calretinin-IR neuron. The density of P2X2 receptor and calretinin-IR neurons also decreased in the submucosal plexus of the I/R-i group. In the myenteric plexus, P2X2-IR, NOS-IR, ChAT-IR and calretinin-IR neurons were reduced in size by 50%, 49.7%, 42%, and 33%, respectively, in the I/R-i group; in the submucosal plexus, P2X2-IR and calretinin-IR neurons were reduced in size by 56% and 72.6%, respectively. These data demonstrate that ischemia/reperfusion of the intestine affects the expression of the P2X2 receptor in neurons of the myenteric and submucosal plexus, as well as density and size of neurons in this population. Our findings indicate that I/R-i induces changes in P2X2-IR enteric neurons that could result in alterations in intestinal motility.

P2X2 purinoreceptor protein in hypothalamic neurons associated with the regulation of food intake

Purines such as ATP act as extracellular messengers through specific purinergic receptors. Three different classes of purinergic receptors have been identified and termed P1, P2X and P2Y. The purinergic receptor subunit P2X2 is a ligand-gated ion channel that is widely expressed by neurons in the central nervous system. The aim of this study was to study the cellular localization and to identify the chemical phenotypes of ionotropic P2X2 receptor (P2X2R)-containing neurons in the rat mediobasal hypothalamus by immunohistochemistry using three different P2X2R antisera, with special reference to neurons that influence food intake and body weight. P2X2R immunoreactivity was mainly observed in cell bodies and neural extensions located in the ventromedial part of the hypothalamic arcuate nucleus, a subregion of the nucleus with a weak blood–brain barrier (BBB). At the subcellular level, P2X2R immunoreactivity was located to the periphery of individual cells, likely representing the plasma membrane. Many P2X2R-immunoreactive cell bodies in the arcuate nucleus contained the orexigenic peptides neuropeptide Y (NPY) and agouti-related protein (AgRP), and the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD). In contrast, P2X2R immunoreactive cell bodies of the arcuate nucles only occasionally contained the anorexigenic peptides α-melanocyte-stimulating hormone (α-MSH) or cocaine- and amphetamine-regulated transcript (CART), or the opioid peptide dynorphin (DYN). There was no evidence for colocalization of P2X2R with somatostatin or neuronal nitric oxide synthase (nNOS) in neurons of the arcuate nucleus. In the parvocellular part of the paraventricular nucleus, P2X2R was demonstrated in some corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH) and CART-containing neurons. In some cell bodies of the lateral hypothalamic area P2X2R was colocalized with DYN. The presence of P2X2R immunoreactivity in primarily orexigenic NPY/AgRP/GABA-containing neurons of the arcuate nucleus suggests that extracellular ATP has a regulatory action on this neuronal population located in a strategic position of the brain.

Changes in P2X receptor responses of sensory neurons from P2X3-deficient mice.

Dorsal root ganglion (DRG) neurons respond to ATP with transient, persistent or biphasic inward currents. In contrast, the ATP responses in nodose neurons are persistent. These sustained currents are also heterogeneous, with one component being accounted for by P2X2/3 receptors, and the residual response probably mediated by P2X2 receptors, although the direct evidence for this has been lacking. In the present study, we examined the P2X receptors on DRG and nodose neurons from P2X3-deficient (P2X3-/-) mice, using whole cell voltage-clamp recording and immunohistochemistry. We found that all P2X3-/- DRG neurons lacked rapidly desensitizing response to ATP, and both DRG and nodose neurons from P2X3-null mutant mice no longer responded to alpha,beta-methylene ATP (alphabetameATP). In contrast, ATP evoked persistent inward current in 12% of DRG neurons and 84% of nodose neurons from P2X3-/- mice. This retained persistent response to ATP on nodose neurons had an EC50 for ATP of 77 microm, was antagonized by Cibacron blue and pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid, potentiated by Zn2+ and acidification, but not enhanced by ivermectin or diinosine pentaphosphate. 2',3'-O-Trinitrophenyl-ATP antagonized this response with an IC50 of 8 microm. All these properties are consistent with those of recombinant P2X2 homomeric receptors. Furthermore, specific P2X2 receptor immunoreactivity detected in wild-type sensory neurons was unaltered in null mutant mice. Therefore, the alphabetameATP-insensitive persistent responses on nodose neurons are likely to be mediated by P2X2 homomers, which contribute to 60% of currents evoked by 100 microm ATP in the wild type.

P2X Receptor Immunoreactivity in Different Arteries from the Femoral, Pulmonary, Cerebral, Coronary and Renal Circulations

The expression of the seven P2X receptor subunits (P2X_1–7) in the rat vascular system was determined using subtype-selective antibodies. Arteries of different sizes (from arterioles to conduit vessels) from a range of vascular beds were used to give an overview of receptor expression. P2X₁ receptor immunoreactivity was detected in the smooth muscle layer of arteries. The relative level of P2X₁ receptor immunoreactivity was dependent on the size of the artery and the vascular bed; expression was highest in small and medium arteries. P2X₄ receptors were detected in all arteries; once again, the relative level of expression was dependent on the size of the artery and the vascular bed. P2X₅ receptor immunoreactivity was barely detectable in most arteries studied. P2X₇ receptor immunoreactivity was generally punctate and associated with the outer adventitial layer. Immunoreactivity for P2X₂, P2X₃ and P2X₆ receptors was not detected in arteries. These results demonstrate that arteries express multiple P2X receptor subunits and that there is a heterogeneity in the level of expression. The properties of artery P2X receptors correspond to homomeric P2X₁ receptors, and the function of P2X₄ and P2X₅ receptor subunits in arteries is unclear.

P2X receptor immunoreactivity in the male genital organs of the rat.

The distribution of ATP ionotropic P2X receptors in the genital organs of the male rat has been investigated with immunohistochemical techniques using specific antibodies to P2X1-7 receptors. In the excretory ducts of the testis (ductus epididymidis, vas deferens and its associated seminal vesicles), the major signals were seen with antibodies to P2X1 and P2X2 in the membranes of the smooth muscle layer, suggesting that these receptors are involved in the process of sperm transport and ejaculation. In the penis body, strong P2X1 and weaker P2X2 immunoreactivity was seen in the smooth muscle of blood vessels and the corpus cavernosum, suggesting a participation in the detumescence process. P2X5 immunoreactivity, a marker for differentiating cells in stratified squamous epithelia, was observed in the epithelia of the terminal urethra, the "horny spur" (spine-studded epithelium of the glans) and the inner surface of the prepuce. Antibodies to P2X3 reacted with nerve fibres in the adventitia of vas deferens, and the P2X6 receptor was localised in the basal lamina of the epithelium. In the prostate, there was immunostaining of the smooth muscle between the tubules with antibody for P2X1, but not with P2X2; P2X3 immunostaining of nerves and strong P2X7 immunostaining of the glandular epithelium of the prostate were also present.

Localization of ATP-gated P2X2 and P2X3 receptor immunoreactive nerves in rat taste buds.

P2X receptors have been suggested to play a role in the transduction of sensory signals such as pain and sound. In the present study, polyclonal antibodies against P2X1 to P2X6 receptors were used to localize P2X receptors in circumvallate and fungiform papillae of rats. Nerve fibres innervating the taste buds stained intensely with P2X3 receptor antibodies. P2X3 receptor-positive nerves were observed in the intra- and subgemmal regions. The nerve fibres were also stained with P2X2 receptor antibodies, but the intensity was much lower. The distribution of P2X2 receptor immunoreactivity overlaps with that of P2X3. These results suggest that ATP might be a neurotransmitter in taste reception cells in the taste buds, where it transducts the taste signals to the afferent taste nerves by activating P2X receptors at the synapses. This is the first experiment indicating such a role for ATP, although supplementary functional studies are required.

Distribution of the P2X2 receptor subunit of the ATP-gated ion channels in the rat central nervous system

The distribution of the P2X2 receptor subunit of the adenosine 5'-triphosphate (ATP)-gated ion channels was examined in the adult rat central nervous system (CNS) by using P2X2 receptor-specific antisera and riboprobe-based in situ hybridisation. P2X2 receptor mRNA expression matched the P2X2 receptor protein localisation. An extensive expression pattern was observed, including: olfactory bulb, cerebral cortex, hippocampus, habenula, thalamic and subthalamic nuclei, caudate putamen, posteromedial amygdalo-hippocampal and amygdalo-cortical nuclei, substantia nigra pars compacta, ventromedial and arcuate hypothalamic nuclei, supraoptic nucleus, tuberomammillary nucleus, mesencephalic trigeminal nucleus, dorsal raphe, locus coeruleus, medial parabrachial nucleus, tegmental areas, pontine nuclei, red nucleus, lateral superior olive, cochlear nuclei, spinal trigeminal nuclei, cranial motor nuclei, ventrolateral medulla, area postrema, nucleus of solitary tract, and cerebellar cortex. In the spinal cord, P2X2 receptor expression was highest in the dorsal horn, with significant neuronal labeling in the ventral horn and intermediolateral cell column. The identification of extensive P2X2 receptor immunoreactivity and mRNA distribution within the CNS demonstrated here provides a basis for the P2X receptor antagonist pharmacology reported in electrophysiological studies. These data support the role for extracellular ATP acting as a fast neurotransmitter at pre- and postsynaptic sites in processes such as sensory transmission, sensory-motor integration, motor and autonomic control, and in neuronal phenomena such as long-term potentiation (LTP) and depression (LTD). Additionally, labelling of neuroglia and fibre tracts supports a diverse role for extracellular ATP in CNS homeostasis.

P2X receptor immunoreactivity in the rat cochlea, vestibular ganglion and cochlear nucleus

P2X receptors have been reported to be involved in neurotransmission in both central and peripheral nerves. In the present study, polyclonal antibodies against P2X 1, P2X 2, P2X 3, P2X 4, P2X 5, and P2X 6 were used to study the distribution of P2X receptors in rat cochlea and vestibulocochlear nerve pathways. It was found that in the vestibular ganglion all six types of antibodies stained the neurons to different intensities. The strongest signal was obtained with the P2X 2 antibodies, followed by P2X 3 antibodies. The other four antibodies produced weak signals, of approximately the same intensity. In the spiral ganglion, the six types of antibodies also stained almost all neurons. However, the rank order of intensity was different from that in the vestibular ganglion: the strongest signal was still obtained with P2X 2 antibodies, followed by P2X 4, P2X 1, and P2X 3 antibodies. The immunolabelling was much weaker with P2X 5 and P2X 6 antibodies compared with the other four types of antibodies. In the cochlea, besides the spiral ganglion neurons, other tissues such as stria vascularis, the organ of Corti and the tectorial membrane were labelled intensively with P2X 2 antibodies only. High density P2X 2 immunoreactivity was also observed in the vestibulocochlear nerve fibres. In the cochlear nucleus, neurons and nerve fibres were stained with the P2X 2 antibodies, as were the neurons in the trapezoid body. These results suggested that P2 receptors, especially the P2X 2 receptors, may play important roles in the signal transduction involved in the perception of sound and balance.

Ultrastructural localisation of ATP-gated P2X2 receptor immunoreactivity in the rat hypothalamo-neurohypophysial system.

The distribution of the P2X(2) subtype of the purine receptor associated with the extracellular signalling activities of ATP was studied in the rat hypothalamo-neurohypophysial system at the electron microscope level. Receptors were labelled with ExtrAvidin-horseradish peroxidase preembedding immunocytochemistry using a polyclonal antibody against a fragment of an intracellular domain of the receptor. Immunoreactivity to P2X(2) receptors was localised in: (i) paraventricular and supraoptic nuclei-in subpopulations of endocrine neurones, neurosecretory and non-neurosecretory axons and dendrites; and (ii) the neurohypophysis-in pituicytes and subpopulation of neurosecretory axons. In both the hypothalamic nuclei examined, labelled asymmetric axo-dendritic synapses were commonly observed. These synapses involved either P2X(2)-labelled axon terminals (synaptic buttons) and unlabelled dendrites or labelled dendrites and unlabelled axon terminals. Axo-somatic synapses established by P2X(2)-positive axons on P2X(2)-positive endocrine cell bodies as well as on P2X(2)-negative somata were also observed. The functional significance of these findings is discussed.