ATP P2X receptors and sensory synaptic transmission between primary afferent fibers and spinal dorsal horn neurons in rats (original) (raw)
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000
The superficial layers of the spinal cord dorsal horn (DH) express P2X2, P2X4, and P2X6 subunits entering into the formation of ionotropic (P2X) receptors for ATP. Using a culture system of laminae I-III from neonatal rat DH, we show that ATP induced a fast nonselective cation current in 38% of the neurons (postsynaptic effect). ATP also increased the frequency of miniature IPSCs (mIPSCs) mediated by GABA(A) receptors or by glycine receptors in 22 and 9%, respectively, of the neurons tested (presynaptic effect) but had no effect on glutamatergic transmission. The presynaptic effect of ATP on GABAergic transmission was not significantly affected by thapsigargin (1 microM) but was completely dependent on Ca(2+) influx. Presynaptic and postsynaptic effects were inhibited by suramin, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, and reactive blue and were not reproduced by uridine 5'-triphosphate (UTP) or adenosine 5'-O-(2-thiodiphosphate) (ADP-beta-S), suggestin...
Pharmacological properties of P2X 3 -receptors present in neurones of the rat dorsal root ganglia
British Journal of Pharmacology, 1998
The electrophysiological actions of several agonists which may dierentiate between P2X 1-and P2X 3receptors were studied under concentration and voltage-clamp conditions in dissociated neurones of 1 ± 4 day old rat dorsal root ganglia. 2 b,g-Methylene-D-ATP (b,g-me-D-ATP) (1 ± 300 mM), diadenosine 5',5'''-P 1 ,P 5-pentaphosphate (AP5A) (100 nM ± 300 mM), diadenosine 5',5'''-P 1 ,P 4-tetraphosphate (AP4A) (300 nM ± 300 mM) and uridine 5'triphosphate (UTP) (1 mM ± 1 mM) all activated concentration-dependent inward currents with a latency to onset of a few ms. 3 The concentration-response curves for b,g-me-D-ATP and AP5A and ATP had similar maximum values, while that for AP4A had a lower maximum. The concentration-response curve to UTP was shallow and did not reach a maximum. b,g-Methylene-L-ATP was virtually inactive. The rank order of agonist potency was ATP4AP5A&AP4A4b,g-me-D-ATP4UTP44b,g-methylene-L-ATP. 4 The inward currents were inhibited by the P2-receptor antagonists suramin (100 mM) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (10 mM). PPADS also inhibited responses to ATP (800 nM) and a,b-methylene ATP (2 mM) in a concentration-dependent manner. 5 This study shows that b,g-me-D-ATP, AP5A, AP4A and UTP all act via a suramin-and PPADSsensitive P2X-receptor to evoke rapid, transient inward currents in dissociated neurones of rat dorsal root ganglia. The very low activity of b,g-methylene-L-ATP suggests that the agonists were acting at the P2X 3-subtype to produce these eects.
Neuroscience Letters, 2001
Adenosine 5 H -triphosphate (ATP) stimulates a [Ca 21 ] i increase via speci®c ionotropic receptors, termed P2X receptors, in rat midbrain presynaptic terminals. A micro¯uorimetric technique enabled study of the [Ca 21 ] i increase in isolated single synaptic terminals, showing that 33.4^2.5% of them responded to ATP. Immunological studies carried out, after functional studies, with speci®c anti-P2X receptor subunit antibodies showed only positive labelling with anti-P2X 3 antibodies in 23.5^1.7% of the terminals. All positively P2X 3 labelled synaptic terminals responded to ATP. Nevertheless, not all of them responded to a,b-meATP, these representing 6.7^1.5% of the total. In addition, 9.8^2.3% of the terminals responded to ATP but exhibit negative P2X 3 -labelling. These results demonstrate the existence of a heterogeneous population of ionotropic ATP receptors at the presynaptic level. q
Distinct Localization of P2X Receptors at Excitatory Postsynaptic Specializations
The Journal of Neuroscience, 2001
ATP mediates fast excitatory synaptic transmission in some regions of the central nervous system through activation of P2X receptors. Nonetheless, the functional significance of ATP-mediated neurotransmission is not yet understood. Using postembedding immunocytochemistry, we describe the distribution of P2X2, P2X4, and P2X6subunits in cerebellum and in the CA1 region of the hippocampus. Dendritic spines of cerebellar Purkinje cells showed immunogold labeling for all three subunits when apposed to parallel fiber (PF) terminals. In contrast, no immunogold labeling was observed on dendritic spines or cell bodies receiving inputs from climbing fibers and basket cells, respectively. In CA1 pyramidal cells, postsynaptic membranes apposed to terminals of Schaffer collaterals were immunogold-labeled for P2X2, P2X4, and P2X6subunits. Immunolabeling was also observed perisynaptically and intracellularly in relation to membranes of the endoplasmic reticulum. The analysis of the tangential dist...
Journal of Neurophysiology, 2003
TNP-ATP-resistant P2X ionic current on the central terminals and somata of rat primary sensory neurons. J Neurophysiol 89: 3235-3242, 2003; 10.1152/jn.01171.2002. P2X receptors have been suggested to be expressed on the central terminals of A␦-afferent fibers innervating dorsal horn lamina V and play a role in modulating sensory synaptic transmission. These P2X receptors have been widely thought to be P2X 2ϩ3 receptors. However, we have recently found that P2X receptor-mediated modulation of sensory transmission in lamina V is not inhibited by trinitrophenyl-adenosine triphosphate (TNP-ATP), a potent antagonist of P2X 1 , P2X 3 homomers, and P2X 2ϩ3 heteromers. To provide direct evidence for the presence of TNP-ATP-resistant P2X receptors on primary afferent fibers, we examined ␣,-methylene-ATP (␣meATP)-evoked currents and their sensitivity to TNP-ATP in rat dorsal root ganglion (DRG) neurons. ␣meATP evoked fast currents, slow currents, and mixed currents that contained both fast and slow current-components. Fast currents and fast current components in the mixed currents were both completely inhibited by 0.1 M TNP-ATP (n ϭ 14). Both slow currents and slow-current components in the mixed currents showed broad spectrum of sensitivity to 1 M TNP-ATP, ranging from complete block (TNP-ATP-sensitive) to little block (TNP-ATP-resistant). TNP-ATP-resistant currents evoked by 10 M ␣meATP could be largely inhibited by 10 M iso-pyridoxalphosphate-6-azophenyl-2Ј,4Ј-disulphonic acid. Cells with P2X currents that were highly resistant to TNP-ATP were found to be insensitive to capsaicin. These results suggest that TNP-ATP-resistant P2X receptor subtypes are expressed on capsaicin-insensitive A␦-afferent fibers and play a role in modulating sensory transmission to lamina V neurons.
Journal of Comparative Neurology, 1999
The distribution of the P2X 2 receptor subunit of the adenosine 5Ј-triphosphate (ATP)gated ion channels was examined in the adult rat central nervous system (CNS) by using P2X 2 receptor-specific antisera and riboprobe-based in situ hybridisation. P2X 2 receptor mRNA expression matched the P2X 2 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, P2X 2 receptor expression was highest in the dorsal horn, with significant neuronal labeling in the ventral horn and intermediolateral cell column. The identification of extensive P2X 2 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.