Age-related changes of sodium-dependent D-[H-3]aspartate and [H-3]FK506 binding in rat brain

We investigated age-related changes in excitatory amino acid transport sites and FK506 binding protein (FKBP) in 3-week-, and 6-, 12-, 18- and 24-month-old Fischer 344 rat brains using receptor autoradiography. Sodium-dependent D-[H-3]aspartate and [H-3]FK506 were used to label excitatory amino acid transport sites and immunophilin (FKBP), respectively. In immature rats (3-week-old), sodium-dependent D-[H-3]aspartate binding was lower in the frontal cortex, parietal cortex, striatum, nucleus accumbens, whole hippocampus, thalamus and cerebellum as compared to adult animals (6-month-old), whereas [H-3]FK506 binding was significantly lower only in the hippocampus, thalamus and cerebellum. [H-3]FK506 binding exhibited no significant change in the brain regions examined during aging. However, sodium-dependent D-[H-3]aspartate binding showed a conspicuous reduction in the substantia nigra in 18-month-old rats. Thereafter, a significant reduction in sodium-dependent D-[H-3]aspartate binding was found in the thalamus, substantia nigra and cerebellum in 24-month-old rats. Other regions also showed about 10-25% reduction in sodium-dependent D-[H-3]aspartate binding. The results indicate that excitatory amino acid transport sites are more susceptible to aging process than immunophilin. Further, our findings demonstrate the conspicuous differences in the developmental pattern between excitatory amino acid transport sites and immunophilin in immature rat brain.