Crutcher, K. A. (1990). Age-related decrease in sympathetic sprouting is primarily due to decreased target receptivity: implications for understanding brain aging. Neurobiology of Aging, 11(3):175-83.
Abstract
Aging of the nervous system is characterized by reduced anatomical
plasticity. The cause of this decreased plasticity is not known
because it is usually not possible to distinguish between extrinsic
and intrinsic factors that affect neuronal growth. One example of
age-related reduced neuronal plasticity that is amendable to such
analysis is the growth of sympathetic axons into the rat hippocampal
formation following septal denervation. This sprouting response can
be elicited throughout the lifespan of the rat but is drastically
reduced in aged animals. The age-related reduction in ingrowth could
theoretically be due to decreased receptivity of the target (reduced
trophic support or increased inhibition of growth), decreased
responsivity of the sympathetic neurons or a combination of both
factors. In order to test the relative contributions of the age of
the target tissue and the age of the sympathetic neurons to the
reduced growth observed in aged animals, superior cervical ganglia
were transplanted from young animals into old animals (y/o) and from
old animals into young animals (o/y) as well as autologously within
the same animals (y/y and o/o). The extent of sympathetic ingrowth
and the survival of transplanted neurons were assessed with
fluorescence histochemical methods. The extent of ingrowth was
significantly greater in young hosts compared with old hosts
regardless of the age of the donor. In addition, the survival of
transplanted neurons was greater in younger hosts than in aged hosts
regardless of donor age. These results indicate that sympathetic
ingrowth is reduced in aging primarily because of decreased
receptivity of the hippocampal target tissue.
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