Topical Seminar: GLUTAMATE RECEPTORS AND THEIR PROTEIN–PROTEIN INTERACTIONS IN PAIN PROCESSING 121 SPINAL CORD INJURY, NEUROPATHIC PAIN AND MICROGLIA S.B. McMahon ° . UK Abstract not available at time of printing. 122 OPIOID PRODUCING IMMUNE CELLS IN INFLAMMATION C. Stein ° . Anesthesiology, Charit´e Campus Benjamin Franklin, Berlin, Germany Opioid receptors are present and upregulated on peripheral sensory nerves, and opioid peptides are expressed in immune cells within peripheral inﬂamed tissue (Nat Med. 9:1003–8, 2003). Environmental stimuli (stress) and releasing agents (corticotropin releasing factor, cytokines, catecholamines) can liberate these peptides to elicit local analgesia, while suppression of the immune system abolishes these effects (J Clin Invest. 100:142−8, 1997; Eur J Neurosci 20:92–100, 2004). These ﬁndings have led to the concept that opioid peptides can be secreted from immunocytes, occupy opioid receptors on sensory nerves and produce analgesia by inhibiting the excitability of these nerves and/or the release of proinﬂammatory neuropeptides. Recent investigations have examined opioid receptor upregulation and G-protein coupling in sensory neurons innervating injured tissue (Mol Pharmacol. 64:202−10, 2003; J Pharmacol Exp Ther. 308:712−8, 2004; Neuroscience 129:473–479, 2004), subcellular pathways of opioid peptide processing and release in immune cells (Endocrinology. 145:1331−41, 2004) and adhesion molecules, chemokines and growth factors governing the migration of opioid containing immune cells to injured tissue (Nat Med. 4:1425−8, 1998; J Neurosci. 22:5588−96, 2002; Br J Pharmacol 142:772–780, 2004; Anesthesiology. 100:149−57, 2004; Pain. 108:67−75, 2004; 112:229–238, 2004). Clinical studies have now shown that small doses of opioids (e.g. morphine) applied into the inﬂamed knee joint can not only produce long lasting pain relief but also decrease synovial inﬂammation (Nat Med. 9:1003−8, 2003; Pain. 83:525−32., 1999). 123 NEUROIMMUNE INTERACTIONS AND NERVE INJURY IN YOUNG RATS: A DEVELOPMENTAL APPROACH TO NEUROPATHIC PAIN M. Fitzgerald ° . Anatomy & Developmental Biology, London Pain Consortium, University College London, London, UK Neuropathic pain occurs in children but the incidence is lower than in adults and tactile allodynia is not observed in rat pup models of nerve injury until 4 weeks of age (Howard et al. 2005). Considerable postnatal development occurs within nociceptive pathways, marked by anatomical, pharmacological and physiological ‘ﬁne-tuning’ over the ﬁrst postnatal weeks (Fitzgerald 2005) and central mechanisms that underlie neuropathic pain in the adult are unlikely to be fully functional in the juvenile animal. Since activated spinal microglia are known to play a key role in the development of tactile allodynia in adult neuropathic pain models, we have examined the microglial response to nerve injury in young rat pups (Moss et al, 2006). Immunohistochemical analysis shows that the dorsal horn microglial response to spared nerve injury (SNI) in postnatal day (P) 10 rat pups is signiﬁcantly less than that observed in adults, 7 days following surgery. To test whether spinal cord microglial responses are generally reduced in young animals, we have compared the effect of spinal lipopolysaccharide (LPS) and N-methyl-D-aspartate (NMDA) application in P10 and adult dorsal horn and concluded that the microglial response to an immune challenge and excitotoxic injury is fully established in the young rat. Furthermore P10 rats develop mechanical allodynia in response to intrathecal lipopolysaccharide. Intrathecal injection of cultured ATPactivated microglia, on the other hand, which is known to cause tactile allodynia after 3 hours in adults (Tsuda et al., 2003), has no behavioural effect at P10. Tactile allodynia following intrathecal injection of ATPstimulated microglia is only observed from P16. These ﬁndings suggest that the unique microglial response and accompanying neuronal sensitivity
triggered by nerve injury is absent in the ﬁrst postnatal weeks and that this may explain the ﬁnding that young rats do not develop tactile allodynia following SNI. We are currently examining the expression proﬁle of several key neuroimmune signalling molecules throughout development and also exploring the developmental regulation of nerve injury induced astrocytic activity. This developmental approach will provide important insights into neuroimmune interactions and neuropathic pain. References Howard RF, Walker SM, Mota PM, Fitzgerald M. The ontogeny of neuropathic pain: postnatal onset of mechanical allodynia in rat spared nerve injury (SNI) and chronic constriction injury (CCI) models. Pain 2005;115:382–389; Fitzgerald M. The development of nociceptive circuits. Nat Rev Neurosci 2005;6:507–520; Tsuda M, Shigemoto-Mogami Y, Koizumi S, Mizokoshi A, Kohsaka S, Salter MW, Inoue K. P2X4 receptors induced in spinal microglia gate tactile allodynia after nerve injury. Nature 2003;424:778–783; Moss A, Beggs S, Vega-Avelaira D, Hathway GJ, Salter MW & Fitzgerald M Spinal microglia and neuropathic pain in young rats: selective lack of nerve injury evoked microglial activation and responses to exogenous ATP-activated microglia (under review).
Topical Seminar: AMPA- & NMDA-TYPE GLUTAMATE RECEPTORS AND THEIR PROTEIN–PROTEIN INTERACTIONS IN PAIN PROCESSING 124 Topical Seminar Summary: AMPA- & NMDA-TYPE GLUTAMATE RECEPTORS AND THEIR PROTEIN–PROTEIN INTERACTIONS IN PAIN PROCESSING S.M. Fleetwood-Walker ° . UK Glutamate plays a key role in pain processing at the spinal cord level. Recent evidence indicates that in addition to NMDA-type glutamate receptors, AMPA-type receptors play a particular role in neuronal plasticity in chronic pain states. This symposium will target key ﬁndings, made using multidisciplinary approaches that deﬁne new roles of NMDA and AMPA receptor subunits together with their molecular interactions in pain processing. 125 ROLES OF NMDA AND AMPA RECEPTORS TOGETHER WITH THEIR INTERACTING PROTEINS IN CHRONIC PAIN STATES S.M. Fleetwood-Walker1 ° , E.M. Garry1 , C. Torsney1 , A.B. MacDermott2 . 1 Centre for Neuroscience Research, Division of Veterinary Biomedical Sciences, Royal (Dick) School of Veterinary Studies, University of Edinburgh, UK, 2 Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, USA Spinal cord pathways that may mediate chronic pain are revealed when spinal inhibition is blocked (Yaksh 1989, Pain 37: 111–123). Superﬁcial NK1 receptor-expressing (NK1R+) dorsal horn neurons are likely to be a component of such circuits. To study these pathways under normal conditions, whole cell patch clamp recordings were made from superﬁcial NK1R+ neurons in the spinal cord slice preparation with attached dorsal root (Torsney and MacDermott 2006, J Neurosci 26: 1833–1843). Lamina I NK1R+ neurons were shown to receive high threshold (Adelta/C ﬁber) monosynaptic input. Blockade of spinal inhibition revealed a novel NMDA receptor-dependent polysynaptic low threshold (Abeta ﬁber) input onto these neurons that may contribute to allodynia in chronic pain states. NMDA receptors are well-established mediators of chronic pain states, and although AMPA receptors are known to participate in basal nociceptive and non-nociceptive transmission, it is becoming clear that they too are involved in sensitised states. New evidence has shed light on how these glutamate receptors may mediate spinal plasticity. The intracellular C-terminal regions of NMDA and AMPA type glutamate receptors associate with