The morphology, neurochemistry, and consequences of sympathosensory plexuses
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The development, maintenance, and survival of neurons depend on the function of neurotrophins such as nerve growth factor (NGF). One population of neurons that rely heavily on NGF for axonal growth and survival is the postganglionic sympathetic neurons. Trauma or disease resulting in injury to the peripheral nervous system causes an increase in the levels of this neurotrophin. This augmentation promotes the collateral sprouting of postganglionic sympathetic axons into those tissues having elevated levels of NGF. Often, NGF-induced sympathetic sprouting occurs in tissues that are normally innervated by these fibers however, high levels of NGF can also promote sprouting of axons into tissues that are normally devoid of sympathetic fibers, such as the sensory ganglia. When postganglionic sympathetic axons grow into the environment of sensory ganglia, they can converge and wrap around a subset of somata (i.e., cell bodies) belonging to primary sensory neurons. This phenomenon, referred to as sympathosensory plexuses is observed in adult mice and rats following peripheral nerve injury, and is also seen in adult transgenic mice that ectopically over express NGF. The overall aim for this project is to examine the morphological and neurochemical features, as well as the overall consequence of sympathosensory plexuses in nerve-injured adult mice and in adult transgenic mice that over express NGF. We hope that this novel information will add to our understanding of the underlying mechanisms associated with the formation of sympathosensory plexuses that occur following injury.