Quantitative analysis of the cervical sympathetic trunk in young adult and aged rats.

The cervical sympathetic trunk of rats aged 4 and 24 months was examined quantitatively with particular reference to the predominating population of unmyelinated axons by using electron microscope photomontages of transverse sections of the entire nerve trunk. No obvious neuropathological or degenerative changes were observed in animals of either age. At 24 months the mean diameter of unmyelinated axons, the mean number of axons/100 microns2 and the mean number of axons associated with individual Schwann cell units was significantly greater than in the young adult animals. With regard to the small population of myelinated axons in the nerve trunk, the thickness of the myelin sheath did not change with age. The numbers of endoneurial blood vessels in the trunk was not significantly different. This analysis of the cervical sympathetic trunk is consistent with other morphological, histochemical and biochemical evidence which suggests that elements of the cervical sympathetic system are well preserved in aged rats.