Journal of Neuroscience, Vol 14, 3048-3058, Copyright © 1994 by Society for Neuroscience
In vivo infusion of NGF induces the organotypic regrowth of perivascular nerves following their atrophy in aged rats
TJ Andrews and T Cowen
Department of Anatomy and Developmental Biology, Royal Free Hospital School of Medicine, London, United Kingdom.
The aim of this study was to investigate whether NGF could reverse the
nerve fiber atrophy exhibited by some neurons in old age. We used
quantitative immunohistochemical techniques to investigate how the
autonomic nerves that supply different blood vessels are affected by aging.
Age changes in the nerve plexus were not widespread but were specific to
particular vascular targets. Furthermore, where nerve fiber atrophy did
occur, it affected different populations of nerves; specifically,
sympathetic nerve fibers were lost from the middle cerebral artery while
nonsympathetic nerves were lost from the tail vein. Peripheral target
tissues have been shown to have a trophic influence on the pattern and
density of their innervation, which declines in old age (Gavazzi et al.,
1992), possibly as a result of decreased availability of neurotrophic
factors such as NGF. Consequently, in an attempt to reverse nerve fiber
atrophy, we used miniosmotic pumps to infuse NGF for 2 weeks over
involuting nerve fibers in the middle cerebral artery of freely moving aged
rats. Our results show that exogenous NGF can induce organotypic neurite
outgrowth from aged neurons undergoing nerve fiber atrophy. Moreover, NGF
can induce a change in the pattern of the old nerve plexus to one similar
to that seen in young animals. NGF had different effects on the extent and
manner of neurite outgrowth in young and aged nerves. NGF induced greater
nerve growth in old compared to young nerves, causing old nerves to grow
within existing nerve bundles and to sprout new nerve fibers, in contrast
to young nerves, which tended to grow only within existing nerve bundles.
In conclusion, this study shows the potential of exogenous NGF to reverse
age-related changes in neuronal morphology.