Expression of adenosine A 2A receptors in the rat lumbar spinal cord and implications in the modulation of N-methyl-d-aspartate receptor currents.
BACKGROUND
The presence of A(2A) receptors in the dorsal horn of the spinal cord remains controversial. At this level, activation of N-methyl-d-aspartate (NMDA) receptors induces wind-up, which is clinically expressed as hyperalgesia. Inhibition of NMDA receptor currents after activation of A(2A) receptors has been shown in rat neostriatal neurons. In this study, we sought to establish the presence of adenosine A(2A) receptors in the lamina II of the rat lumbar dorsal horn neurons and investigated whether the activation of A(2A) receptors is able to modulate NMDA receptor currents.


METHODS
Experiments were conducted in the rat lumbar spinal cord. The presence of adenosine A(2A) receptor transcripts inside the lumbar spinal cord is assessed with the reverse transcriptase polymerase chain reaction (RT-PCR) technique. Western blot experiments are performed at the same level. The RT-PCR technique is also performed specifically in the lamina II, and the presence of adenosine A(2A) receptor transcripts is assessed in neurons from the lamina II with the single-cell RT-PCR technique. The effect of adenosine A(2A) receptor activation on NMDA receptor currents is studied by the whole-cell configuration of the patch clamp technique.


RESULTS
RT-PCR performed on the lumbar spinal cord revealed the presence of adenosine A(2A) receptor transcripts. Western blot experiments revealed the presence of A(2A) receptors in the lumbar spinal cord. RT-PCR performed on the substantia gelatinosa also revealed the presence of adenosine A(2A) receptor transcripts. Finally, single cell RT-PCR revealed the presence of adenosine A(2A) receptor transcripts in a sample of lamina II neurons. Patch clamp recordings showed an inhibition of NMDA currents during the application of a selective A(2A) agonist.


CONCLUSIONS
These results demonstrate the presence of A(2A) receptor on neurons from the substantia gelatinosa of the rat lumbar dorsal horn and the inhibition of NMDA-induced currents by the application of a selective A(2A) receptor agonist. Therefore, A(2A) receptor ligands could modulate pain processing at the spinal cord level.
Guntz
Emmanuel
E
Department of Anesthesiology, Hôpital Universitaire Saint-Pierre, Université Libre de Bruxelles, Brussels, Belgium. eguntz@ulb.ac.be
Dumont
Hélène
H
Pastijn
Els
E
d'Exaerde
Alban de Kerchove
Ade K
Azdad
Karima
K
Sosnowski
Maurice
M
Schiffmann
Serge N
SN
Gall
David
D
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists; D000818:Animals; D015153:Blotting, Western; D005998:Glycine / Q000378:metabolism; D008161:Lumbosacral Region; D008564:Membrane Potentials; D016202:N-Methylaspartate / Q000378:metabolism; D010146:Pain / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010627:Phenethylamines / Q000494:pharmacology; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D043705:Receptor, Adenosine A2A / Q000235:genetics / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013376:Substantia Gelatinosa / Q000378:metabolism
D058908:Adenosine A2 Receptor Agonists; D010627:Phenethylamines; D012333:RNA, Messenger; D043705:Receptor, Adenosine A2A; D016194:Receptors, N-Methyl-D-Aspartate; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D016202:N-Methylaspartate; D000241:Adenosine; D005998:Glycine