ABSTRACT
The localizations of efferent and afferent neurons were observed following injection of neural tracers, cholera toxin B subunit (CTB) and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the rat thymus with ages. Thirty Sprague-Dawley rats were examined at 3 weeks, 5~6 and 20 months of age. After survival times of 48~96 hours following injection of neural tracers, the rats were perfused and their brain, spinal cord, sympathetic ganglia, dorsal root ganglia and vagal ganglia were frozen sectioned (40 mm). These sections were stained by CTB immunohistochemical and HRP histochemical staining methods, and observed with polarized dark and light microscope. The results were as follows: 1. WGA-HRP and CTB labeled parasympathetic neurons were bilaterally seen in the nucleus ambiguus and medullary reticular formation of medulla with all ages. 2. WGA-HRP labeled sympathetic neurons were bilaterally labeled in superior cervical ganglia, middle cervical ganglia, stellate ganglia and T4-8 sympathetic chain ganglia. The number of labeled sympathetic neurons was increased in the thymus at 20 months of age. According to the aging, sympathetic neuronal processes were more developed, and the nerve fibers were coarse and more branched. 3. WGA-HRP labeled sensory neurons were bilaterally observed within the vagal and C1-6 dorsal root ganglia. The number of labeled sensory neurons was decreased in the thymus at 20 months of age.