Age-related levels of GABA/benzodiazepine binding sites in cerebrum of F-344 rats: effects of exercise.

We examined gamma-aminobutyric acid (GABA), benzodiazepine and convulsant sites of postsynaptic GABA/benzodiazepine receptors (GBZR) in cerebral membranes of inbred Fischer 344 male rats as a function of age. In aged rats (23 to 24 months), the benzodiazepine binding site as determined by [3H]flunitrazepam was 47% and 43% lower than corresponding values in young adult (3 to 4 months) and mature (10 to 12 months) rats, respectively. The decrease was due to the loss of binding density rather than a change in affinity. No statistically significant age-related changes in [3H]muscimol binding were observed when 5 nM or 40 nM labeled muscimol were used. GABA produced a dose-dependent stimulation of flunitrazepam binding in all age groups, but the maximum stimulation in aged animals was significantly higher (24%) than in young and mature animals. The [35S]TBPS binding site, the convulsant site of GABA/benzodiazepine receptors, was unaffected with age. We also studied the effects of exercise on GBZR binding sites of aged rats. The decline of flunitrazepam binding sites and the high sensitivity of flunitrazepam binding to regulation by GABA in aged animals were reversed by 8 to 10 weeks of endurance exercise. Endurance exercise did not have any significant effect on muscimol or TBPS binding sites. Results suggest that there are aged-related alterations of GBZR binding sites and that these modifications can be reversed by exercise.