Expression of Adenosine A2A Receptors in the Rat Lumbar Spinal Cord and Implications in the Modulation of N-Methyl-d-Aspartate Receptor Currents

Abstract

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.

How does adenosine control neuronal dysfunction and neurodegeneration?

“…Thus, A 2A R are selective controllers of adaptive changes of synaptic efficiency. This is in accordance with the ability of A 2A R to enhance the evoked release of glutamate in different brain areas (Lopes et al 2002;Marchi et al 2002;Rodrigues et al 2005;Ciruela et al 2006a;Shen et al 2013;Matsumoto et al 2014;Machado et al 2016) and the function of ionotropic glutamate receptors (Wirkner et al 2004;Guntz et al 2008;Rebola et al 2008;Azdad et al 2009;Higley and Sabatini 2010;Dias et al 2012;Scianni et al 2013;Di Angelantonio et al 2015;Sarantis et al 2015). A 2A R also act as fine-tuners of other neuromodulation systems (Ribeiro 1999;Ribeiro 2000, 2009), since A 2A R activation is required to observe synaptic effects of growth factors (Di ogenes et al 2004;Flajolet et al 2008;Gomes et al 2009) or neuropeptides (Sebastião et al 2000a;Cunha-Reis et al 2007).…”

Genetic deletion of the adenosine A2A receptor in mice reduces the changes in spinal cord NMDA receptor binding and glucose uptake caused by a nociceptive stimulus

“…In addition to these behavioural changes, we found a large reduction in the level of Conflicting results have been obtained from binding studies and autoradiography [3,7,8], and functional studies have reported some inconsistent effects of A 2A receptor ligands [1,5,15,16,25,28,36]. mRNA for the A 2A receptor has been reported to be expressed in the dorsal root ganglion but not in the spinal cord [20,21] suggesting that A 2A receptors could be present on the peripheral terminals of the sensory nerves but not to any significant extent in the spinal cord, as suggested by Sawynok [32].…”

“…More recent studies have however detected mRNA for the A 2A receptor in rat and mouse spinal cord [6,16], and it has been suggested that these may on be on …”

The therapeutic potential of interleukin-10 in neuroimmune diseases

“…A2ARs are found on both glial cells (Gyoneva et al, 2009) and neurons (Guntz et al, 2008) and activation following inflammation has been shown to increase IL-10 and decrease proinflammatory molecules released from a variety of different inflammatory cell types in culture (Grinberg et al, 2009; Hasko et al, 1996; Khoa et al, 2001; Link et al, 2000; Perez-Aso et al, 2013; Vincenzi et al, 2013a, 2013b). Interestingly, the A2AR is upregulated on macrophages and microglia following inflammatory signals such as LPS, CpG, lipoteichoic acid, or TNF, and on lymphocytes from MS and ALS patients, providing a unique pharmacological target for immune cells and glia exclusively activated by prior proinflammatory signals (Grinberg et al, 2009; Gyoneva et al, 2009; Vincenzi et al, 2013a, 2013b).…”