Recent studies of cytokine actions in the spinal cord and dorsal root ganglia suggest that neuron-glia interactions are important in initiating and maintaining chronic pain states. How this is accomplished remains unclear. Disorders of the orofacial complex often produce intense chronic pain in patients and results in devastating consequences in their well being. The long-term goal of this research is to understand neuron-glia interactions in the trigeminal ganglion (TG), the primary afferent structure for the orofacial region. Our focus will be to understand the critical role that transmitters released from neuronal somata (cell bodies) of TGs play in neuron- satellite glial cell communication. We hypothesize that excessive firing in TG neurons elicits somatic release of ATP from neuronal somata. ATP activates satellite cells and evokes cytokine release from these cells. Cytokines in turn sensitize the neuronal somata and further increase their activity. In vitro and in vivo approaches will be used to test this hypothesis of positive feedback loop. We will (1) identify the transmitters released from neuronal somata of TGs (2) examine the communication between neuron and satellite cells (3) determine the effects of cytokines on P2X and TRPV receptor-mediated responses, (4) examine the action of cytokines on nociceptive responses in rats and determine the possibility of using siRNA to down-regulate receptors involved in neuron-glia communication and thus to relieve orofacial nociception. Normal, inflamed and nerve-ligated rats will be used. Transmitter release and membrane currents will be measured with patch pipettes;intracellular Ca2+ concentrations will be monitored with Ca2+ dyes;expression of P2X and TRPV receptors will be examined with immunocytochemistry and Western analyses. These studies should provide a better understanding of the mechanisms underlying neuron-glia interactions in TGs. The knowledge will be critical for designing better therapies for the treatment of orofacial pain.
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