Ultrastructural analysis of lymph node innervation in the rat.

The morphological analysis of nerves in axillary lymph nodes of the rat revealed the presence of two types of axon possessing either a more or a less electron-lucent matrix. The more electron-lucent axons enter the node finely myelinated, do not contain synaptic vesicles and quickly divide to form branches approaching the basement membranes of blood vessels, as well as cellular elements. They may be interpreted as sensory axons. The less electron-lucent axons are unmyelinated, and contain three distinct populations of synaptic vesicles. These may all be present in one axonal varicosity, so that the existence of cotransmitters is highly probable.