Morphological evidence for the maintenance of the cervical sympathetic system in aged rats.

Elements of the cervical part of the sympathetic nervous system have been examined quantitatively in four and twenty-four month Wistar rats. The number of unmyelinated axons in the cervical trunk had significantly (P less than 0.002) increased in the old animals and the number of myelinated axons comprised less than 4% of the total number at both ages. The number of neurons in the superior cervical ganglion and the density of noradrenergic innervation of two of its target organs, the iris and the submandibular gland, were insignificantly different at the two ages. These results are consistent with other evidence which suggests that the cervical sympathetic system is maintained throughout the adult lifespan in rats.