Role of spinal P2Y6 and P2Y11 receptors in neuropathic pain in rats: possible involvement of glial cells

Background: The participation of spinal P2X receptors in neuropathic pain is well recognized. However, the role of P2Y receptors has been less studied. The purpose of this study was to investigate the contribution of spinal P2Y(6,11) receptors following peripheral nerve damage induced by spinal nerve ligation. In addition, we determined the expression of P2Y(6,11) receptors in the dorsal spinal cord in presence of the selective P2Y(6,11) receptors antagonists. Furthermore, we evaluated the participation of spinal microglia and astrocytes in the pronociceptive role of P2Y(6,11) receptors. Results: Spinal administration of the selective P2Y(6) (MRS2578, 10-100 mu M) and P2Y(11) (NF340, 0.3-30 mu M) receptor antagonists reduced tactile allodynia in spinal nerve ligated rats. Nerve injury increased the expression of P2Y6,11 receptors at 7, 14 and 21 days after injury. Furthermore, intrathecal administration of MRS2578 (100 mu M/day) and NF340 (30 mu M/day) for 3 days significantly reduced spinal nerve injury-induced increase in P2Y(6,11) receptors expression, respectively. Spinal treatment (on day 14 after injury) with minocycline (100 mu g/day) or fluorocitrate (1 nmol/day) for 7 days reduced tactile allodynia and spinal nerve injury-induced up-regulation in Iba-1 and GFAP, respectively. In addition, minocycline reduced nerve injury-induced up-regulation in P2Y(6,11) receptors whereas that fluorocitrate diminished P2Y(11), but not P2Y(6), receptors up-regulation. Intrathecal treatment (on day 21 after injury) with the selective P2Y(6) (PSB0474, 3-30 mu M) and P2Y11 (NF546, 1-10 mu M) receptor agonists produced remarkable tactile allodynia in nerve ligated rats previously treated with minocycline or fluorocitrate for 7 days. Conclusions: Our data suggest that spinal P2Y(6) is present in spinal microglia while P2Y(11) receptors are present in both spinal microglia and astrocytes, and both receptors are up-regulated in rats subjected to spinal nerve injury. In addition, our data suggest that the spinal P2Y6 and P2Y(11) receptors participate in the maintenance of neuropathic pain.