Patterns of neurotrophin protein levels in male and female Fischer 344 rats from adulthood to senescence: how young is "young" and how old is "old"?

The current study assessed neurotrophin protein levels in male and female rat brain tissues at four different ages ranging from postpuberty to senescence. In both sexes nerve growth factor (NGF) increased, and brain-derived neurotrophic factor (BDNF) decreased, from 4 to 24 months of age. Using a slightly older age for the young group, or a slightly younger age for the aged group, had profound effects on whether age effects were realized. There were no sex differences in the pattern of change in neurotrophin levels across age, and neurotrophin levels did not correlate with estrogen levels in females or estrogen or testosterone levels in males. The current findings suggest that profound changes in neurotrophin protein levels can occur within only a few months time, and that these changes influence whether age-related neurotrophin alterations are realized.