We employed experimental degeneration, tract-tracing with wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP) and electron microscopy to explore the postganglionic sympathetic fibers in the hypoglossal nerve of hamsters. Quantitative results of normal untreated animals at the electron microscopic level showed the existence of unmyelinated fibers, which made up about 20% of the total fibers in the nerve, being more numerous on the left side. The nerve fibers were preferentially distributed at the periphery of the nerve. Following superior cervical ganglionectomy, most of the unmyelinated fibers underwent degenerative changes. Tract-tracing studies showed that some of the unmyelinated fibers were labeled by WGA-HRP injected into the superior cervical ganglion (SCG). It is suggested that the unmyelinated fibers represent the postganglionic sympathetic fibers originated from the SCG.
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