Clinically peripheral nerve injury and regeneration is a common occurrence. Normal regeneration results in faulty localization of stimuli, increased two point discrimination thresholds and general hypersensitivity, ranging from relativity innocuous hyperesthesia often described as unusual or vivid sensations to allodynia or causalgia which are debilitating painful sensations often elicited by innocuous cutaneous stimuli. Although most of these symptoms show improvement with time others, most notably the pain syndromes, can last for years and greatly affect an individual's quality of life. Our major goal in this proposal is to understand the cellular processes that underlie plasticity in sensory neurons following peripheral nerve injury. Specifically, we will look at the effects of target-derived trophic factor signaling induced plasticity of primary sensory neurons re-innervating the skin. We have now shown that many types of regenerated cutaneous afferent fibers show increased sensitivity following regeneration. In another series of studies we examined the effects of overexpression of trophic factors in the skin. Depending on the factor expressed we found that different types of cutaneous sensory neurons were sensitized to mechanical and thermal stimuli. In addition we found that there was an increase in specific combinations of receptors/channels that are believed to be involved in the transduction of peripheral stimuli by sensory neurons (e.g. TRP and ASIC channels). Finally, we found that the expression of these same trophic factors and receptors/channels is increased in the DRG and skin respectively following nerve injury. We hypothesize that the increase in trophic signaling results in the increased expression of several TRP and ASIC channels in regenerating cutaneous fibers resulting in an increased sensitivity to peripheral stimuli. Here we propose to use a novel in vivo siRNA procedure which allows us to knock down the expression of individual receptors/channels specifically in the regenerating cutaneous fibers and an ex vivo recording preparation to directly test this hypothesis. Evaluation of our hypotheses and the determination of the specific signaling events receptors/channels responsible for sensitization of these fibers will provide new insights to these processes and more importantly could provide potential targets for the development of pharmaceutical therapies. These new therapies could provide for improved functional recovery following regeneration as well as alleviation of the adverse symptoms and potential chronic pain syndromes.
Peripheral nerve injury and subsequent regeneration often leads to a variety of sensory deficits including chronic pain syndromes. In this application we are proposing to determine specific cellular and molecular changes in sensory neurons that could lead to these symptoms. Determination of these mechanisms could provide targets for new pharmaceutical therapies that could provide for improved functional recovery following regeneration as well as alleviation of the adverse syndromes.
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