Localized protein synthesis provides a means for the distal processes of the neuron to rapidly and autonomously respond to its environment. Although best characterized in the dendritic compartment, work over the past 5 years has proven that axons are capable of locally generating new proteins. In dendrites, activity-dependent local protein synthesis plays a role in synaptic plasticity. There is also evidence for activity-dependent protein synthesis in axons. Given the complex population of proteins synthesized in axons, it is likely that axonally synthesized proteins also play a role in the function of mature axons. The central hypothesis of this proposal is that changes in local protein synthesis in sensory axons alter the neuron's capacity for propagating noxious stimuli. The objective of this proposal is to understand how axonal transport and local protein synthesis contribute to hyperexcitability exhibited by damaged neurons leading to neuropathic pain states. We will use in vitro and in vivo methods to determine if the transport and sub-axonal localization of ion channel and neurotpeptide mRNAs are altered in neuropathic pain, and whether locally synthesized ion channels are functionally inserted into axoplasmic membranes and if this translation and trafficking are altered by neuropathic pain-associated stimuli. We will utilized chimeric mRNA reporter constructs to address axonal localization of these transcripts, both in cultured primary sensory neurons and in transgenic mice. GFP-tagged fusion proteins of locally synthesized ion channel proteins will be used to determine the functional relevance of axonally synthesized ion channels, with the ultimate goal of understanding how axonal trafficking and local synthesis of these proteins contributes to neuropathic pain. Neuropathic pain, the chronic pain experienced following injury, infection, or inflammation of peripheral nerves, sharply contrasts with normal pain, both is the molecular mechanisms which cause it and in their responses to conventional pain treatments. Current animal models of nerve trauma have provided some insights into the neuronal changes that occur in response to peripheral nerve damage - revealing a remarkable degree of plasticity in both the sensory neurons and spinal cord. Understanding how axonal transport and local protein synthesis contribute to increased hyperexcitability of these damaged sensory neurons may point to alternative methods of treating pathological pain states.
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