Thymic innervation in the rat: a light and electron microscopical study.
The innervation of the rat thymus was studied by light and electron microscopy in juvenile and aged rats. By light microscopy numerous fine nerves were found in the connective tissue septa penetrating between the thymic lobules. These septa were clearly delineated in the juvenile animals, but indistinct in the aged rats, thus creating the spurious impression that thymic parenchyma contains nerves. In the aged animals the nerves are thicker, tortuous, and more branched than in juvenile animals. Electron microscopy confirms the light microscopic observations: no nerves were found within the thymic parenchyma. The thymic capsule and larger connective tissue septa contain bundles of myelinated and unmyelinated axons, surrounded by a perineural sheath. Within the extraparenchymal compartment, which is greatly enlarged in aged animals, efferent and sensory nerves, devoid of perineurium, were found to contact mainly reticular cells, and in rare instances plasma cells and lymphocytes. The majority of axonal varicosities are not closely related to cellular elements, and, in general, vesicles are relatively infrequent. The possible functional significance of these observations is discussed.
Novotny
G E
GE
Abt. Neuroanatomie, Zentrum für Anatomie und Hirnforschung, Universität Düsseldorf, Federal Republic of Germany.
Sommerfeld
H
H
Zirbes
T
T
D000375:Aging; D000818:Animals; D001369:Axons / Q000648:ultrastructure; D004848:Epithelium / Q000648:ultrastructure; D008214:Lymphocytes / Q000648:ultrastructure; D008854:Microscopy, Electron; D009474:Neurons / Q000166:cytology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D013950:Thymus Gland / Q000254:growth & development / Q000294:innervation* / Q000648:ultrastructure