Peripheral inflammation upregulates P2X receptor expression in satellite glial cells of mouse trigeminal ganglia: A calcium imaging study Raya Kushnir, Pavel S. Cherkas, Menachem Hanani * Laboratory of Experimental Surgery, Hadassah-Hebrew University Medical Center, Mount Scopus, Jerusalem 91240, Israel article info Article history: Received 20 December 2010 Received in revised form 13 May 2011 Accepted 17 May 2011 Keywords: Adenosine triphosphate (ATP) Pain Sensory ganglia Inflammation Purinergic receptors abstract Satellite glial cells (SGCs) in sensory ganglia are altered structurally and biochemically as a result of nerve injury. Whereas there is ample evidence that P2 purinergic receptors in central glial cells are altered after injury, there is very little information on similar changes in SGCs, although it is well established that SGCs are endowed with P2 receptors. Using calcium imaging, we characterized changes in P2 receptors in SGCs from mouse trigeminal ganglia in short-term cultures. Seven days after the induction of submandibular inflammation with complete Freund’s adjuvant, there was a marked increase in the sensitivity of SGCs to ATP, with the threshold of activation decreasing from 5 mM to 10 nM. A similar observation was made in the intact trigeminal ganglion after infra-orbital nerve axotomy. Using phar- macological tools, we investigated the receptor mechanisms underlying these changes in cultured SGCs. We found that in control tissues response to ATP was mediated by P2Y (metabotropic) receptors, whereas after inflammation the response was mediated predominantly by P2X (ionotropic) receptors. As the contribution of P2X1,3,6 receptors was excluded, and the sensitivity to a P2X7 agonist did not change after inflammation, it appears that after inflammation the responses to ATP are largely due to P2X2 and/ or 5 receptors, with a possible contribution of P2X4 receptors. We conclude that inflammation induced a large increase in the sensitivity of SGCs to ATP, which involved a switch from P2Y to P2X receptors. We propose that the over 100-fold augmented sensitivity of SGCs to ATP after injury may contribute to chronic pain states. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Receptors for ATP and related nucleotides were identified in central and peripheral neurons, and there is ample evidence that signaling via nucleotide P2 receptors (P2Rs) is an important mode of neuronal communication (for reviews see Illes and Ribeiro, 2004; North and Verkhratsky, 2006; Burnstock, 2007; Abbracchio et al., 2009). Two main receptor types mediate the effects of P2R agonists: P2X receptors (P2XRs), which are ligand-gated ion chan- nels, and P2YRs, which are G protein-coupled (Abbracchio et al., 2009). Each of these receptor types has several subtypes with a variety of actions and distributions in the nervous system (Burnstock, 2007). P2Rs play a role in synaptic transmission (Halassa et al., 2009) and in mediating trophic actions of nucleotides on glial cells and neurons (Neary and Zimmermann, 2009). In recent years there has been a growing interest in P2Rs in glial cells, and it appears that ATP that is released from neurons and also from glia may act on P2Rs in glial cells (for review see Fields and Burnstock, 2006). Activation of these receptors may increase intracellular Ca 2þ concentration ([Ca 2þ ] in ) in glia, and contribute to Ca 2þ wave generation, which in turn can alter neuronal excitability (Scemes and Giaume, 2006). ATP is thus established as a signaling mole- cule among glial cells and between neurons and glial cells. It is becoming clear that glial cells participate in various patho- logical changes in the nervous system, and one aspect that attracted considerable attention is that microglia in the spinal cord are closely involved in mechanisms of chronic pain. Tsuda et al. (2003) have found that P2X4Rs in microglia are upregulated following axotomy and that this change is essential for the generation and maintenance of chronic pain. It thus appears that glial activation (gliosis) in the CNS is part of the changes underlying chronic pain. Further studies largely supported these observations (Guo et al., 2005), for reviews see Inoue and Tsuda (2009) and Jarvis (2010). In recent years there has been an increasing interest in glial cells in sensory ganglia, in particular those that form an envelope around sensory neurons. These cells, termed ’satellite glial cells’ (SGCs) are greatly altered by peripheral damage, and undergo changes consistent with activation, as observed in the CNS glia (for reviews * Corresponding author. Tel.: þ972 2 5844721; fax: þ972 2 5844080. E-mail address: hananim@cc.huji.ac.il (M. Hanani). Contents lists available at ScienceDirect Neuropharmacology journal homepage: www.elsevier.com/locate/neuropharm 0028-3908/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropharm.2011.05.019 Neuropharmacology 61 (2011) 739e746