This NIH-supported research program has the long-term objective of elucidating the central mechanisms and neuroplastic processes underlying acute and chronic dental and orofacial pain conditions and their control. Recent data indicate that stimulation of the tooth pulp with an inflammatory irritant induces a 'central sensitization' of nociceptive neurons in the rat brainstem and thalamus and that the brainstem subnucleus caudalis ('medullary dorsal horn') is strategically involved. NMDA receptors (NMDAR) are also involved in this process that has been implicated in the allodynia, hyperalgesia and spread and referral of pain that may occur after injury and inflammation. Purinergic receptor (P2XR) mechanisms have been recently identified as another modulatory process in spinal nociceptive transmission that may function through a powerful presynaptic regulation of glutamate release in the spinal dorsal horn. There has been no study of purinergic mechanisms in central nociceptive processing in the orofacial region, other than some recent preliminary data from our laboratory that indirectly suggests these mechanisms may operate in caudalis. We therefore propose in vivo and in vitro experiments to determine (i) if the pulp-induced central sensitization in caudalis nociceptive neurons involves endogenous purinergic mechanisms; if so, (ii) whether these mechanisms are presynaptic; and (iii) whether they are NMDA receptor dependent. Our experimental design will allow us to test in vivo the involvement of endogenous purinergic mechanisms in pulp-induced central sensitization in functionally identified single neurons in Vc and their potential for regulation of glutamate release and NMDAR activation. The in vivo experiments will be supplemented by in vitro experiments that will provide important additional insights into the P2XR subtype involved and whether the purinergic receptor mechanisms are operating presynaptically. These studies will provide new information on a novel chemical mediator of nociceptive transmission, and new insights will be gained of the central processing of sensory information from the tooth pulp. These insights could be important in the development of improved therapeutic approaches for the prevention of pain associated with pulpal inflammation and for the relief of pain once it has been initiated.
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