Participation of peripheral P2Y1, P2Y6 and P2Y11 receptors in formalin-induced inflammatory pain in rats

• Peripheral P2Y1, 6, 11 agonists increased formalin-induced pain.
• Peripheral P2Y1, 6, 11 selective antagonists reduced formalin-induced pain.
• P2Y1, 6, 11 antagonists prevented the pronociceptive effect of their agonists.
• P2Y1, 6, 11 receptor proteins are expressed in the primary afferent fibers.
• Peripheral P2Y1, 6, 11 receptors play a pronociceptive role in the formalin test.

Metabotropic P2Y receptors subfamily consists of eight functional mammalian receptors. Specifically, P2Y1, P2Y6 and P2Y11 receptors have been described in the sensory nervous system, but their participation, at peripheral level, in behavioral pain models is scarcely understood. This study assessed the role of peripheral P2Y1, P2Y6 and P2Y11 receptors in formalin-induced inflammatory pain. Ipsilateral, but not contralateral peripheral pre-treatment with the endogenous P2Y1 (ADP, 100–1000 nmol/paw), P2Y6 (UDP, 180–300 nmol/paw) and P2Y11 (ATP, 100–1000 nmol/paw), or selective P2Y1 (MRS2365, 0.1–10 nmol/paw), P2Y6 (PSB0474, 0.1–0.10 pmol/paw) and P2Y11 (NF546, 0.3–3 nmol/paw) receptor agonists increased 0.5% formalin-induced flinching behavior. Concordantly, peripheral pre-treatment with the selective P2Y1 (MRS2500, 0.01–10 pmol/paw), P2Y6 (MRS2578, 3–30 nmol/paw) and P2Y11 (NF340, 1–10 nmol/paw) receptor antagonists significantly decreased 1% formalin-induced flinching behavior. Furthermore, the pronociceptive effect of ADP (100 nmol/paw) or MRS2365 (10 nmol/paw), UDP (300 nmol/paw) or PSB0474 (10 pmol/paw) and ATP (1000 nmol/paw) or NF546 (3 nmol/paw) was blocked by the selective P2Y1 (MRS2500, 0.01 nmol/paw), P2Y6 (MRS2578, 3 nmol/paw), and P2Y11 (NF340, 1 nmol/paw) receptor antagonists, respectively. Western blot analysis confirmed the presence of P2Y1 (66 kDa), P2Y6 (36 kDa) and P2Y11 (75 kDa) receptors in dorsal root ganglia (DRG) and sciatic nerve. Results suggest that peripheral activation of P2Y1, P2Y6 and P2Y11 receptors plays a pronociceptive role in formalin-induced pain.