Neuronal P2X₇Receptors Are Targeted to Presynaptic Terminals in the Central and Peripheral Nervous Systems

Abstract

The ionotropic ATP receptor subunits P2X(1-6) receptors play important roles in synaptic transmission, yet the P2X(7) receptor has been reported as absent from neurons in the normal adult brain. Here we use RT-PCR to demonstrate that transcripts for the P2X(7) receptor are present in extracts from the medulla oblongata, spinal cord, and nodose ganglion. Using in situ hybridization mRNA encoding, the P2X(7) receptor was detected in numerous neurons throughout the medulla oblongata and spinal cord. Localizing the P2X(7) receptor protein with immunohistochemistry and electron microscopy revealed that it is targeted to presynaptic terminals in the CNS. Anterograde labeling of vagal afferent terminals before immunohistochemistry confirmed the presence of the receptor in excitatory terminals. Pharmacological activation of the receptor in spinal cord slices by addition of 2'- and 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP; 30 microm) resulted in glutamate mediated excitation of recorded neurons, blocked by P2X(7) receptor antagonists oxidized ATP (100 microm) and Brilliant Blue G (2 microm). At the neuromuscular junction (NMJ) immunohistochemistry revealed that the P2X(7) receptor was present in motor nerve terminals. Furthermore, motor nerve terminals loaded with the vital dye FM1-43 in isolated NMJ preparations destained after application of BzATP (30 microm). This BzATP evoked destaining is blocked by oxidized ATP (100 microm) and Brilliant Blue G (1 microm). This indicates that activation of the P2X(7) receptor promotes release of vesicular contents from presynaptic terminals. Such a widespread distribution and functional role suggests that the receptor may be involved in the fundamental regulation of synaptic transmission at the presynaptic site.

Ecto-Nucleotidases and Nucleoside Transporters Mediate Activation of Adenosine Receptors on Hippocampal Mossy Fibers by P2X7Receptor Agonist 2′-3′-O-(4-Benzoylbenzoyl)-ATP

“…On the other hand, on the basis of our data, we cannot completely exclude that in addition to some P2X 7 -like antigen there are some "true" P2X 7 receptors present on mossy fiber terminals that act exclusively on targets that are not involved in synaptic transmission; however, we consider this very unlikely, because in a former study (Kukley et al, 2001) we used another antibody directed against P2X 7 and detected no labeling of the mossy fiber projection at all (our unpublished observation). Because all studies that reported presynaptic P2X 7 used the same antibody (raised against residues 576 -595 of rat P2X 7 ; Alomone Labs, Chemicon, Temecula, CA), it will be interesting to see whether future studies can confirm the presence of presynaptic P2X 7 at other nerve terminals (Deuchars et al, 2001;Miras-Portugal et al, 2003;Atkinson et al, 2004;Puthussery and Fletcher, 2004).…”

“…It was reported recently, however, that P2X 7 subunits are localized on presynaptic terminals and modulate transmitter release onto hippocampal and spinal cord neurons (Deuchars et al, 2001;Armstrong et al, 2002;Sperlagh et al, 2002). The presence of Ca 2ϩ -permeable P2X 7 receptors on hippocampal mossy fiber terminals (Armstrong et al, 2002;Sperlagh et al, 2002) would be particularly intriguing, because mossy fiber synapses display several forms of short and long-term synaptic plasticity that depend on the accumulation of presynaptic Ca 2ϩ (Castillo et al, 1994;Regehr et al, 1994;Salin et al, 1996;Dietrich et al, 2003).…”

The role of P2X7 receptors in tissue fibrosis: a brief review

“…The stoichiometry of P2X 7 R involves a trimeric pore that consists of homomultimers [23]. The P2X 7 R is predominantly expressed on cells of hematopoietic origin such as monocytes [24], dendritic cells, T and B lymphocytes, eosinophils, mast cells, but also on various types of glia within the peripheral and central nervous system including microglia, astrocytes, oligodendrocytes, and Schwann cells [25,26]. Moreover, P2X 7 R protein is expressed on epithelial cells, osteoblasts, synoviocytes, and fibroblasts [27][28][29][30].…”

Input-Specific Modulation of Neurotransmitter Release in the Lateral Horn of the Spinal Cord via Adenosine Receptors

“…This is pertinent because in this region, the source of adenosine and the conditions under which it is released are unresolved. In other autonomic regions, a major source of adenosine may be attributable to the extracellular metabolism of ATP (St. Lambert et al, 1997), and because SPNs are excited by activation of the P2X 7 receptor, whose endogenous ligand is ATP (Deuchars et al, 2001c), it is likely that this is the case in the IML.…”