Effects of chronic treatment with a cyclic AMP-selective phosphodiesterase inhibitor, rolipram, on excitatory amino acid neurotransmission systems in young and aged rat brains.

Rolipram selectively inhibits cyclic AMP-specific phosphodiesterase, and leads to an increase in cyclic AMP levels in the brain. In this study, we investigated the effects of chronic rolipram treatment on excitatory and inhibitory amino acid neurotransmission systems in young and aged Wistar rat brains. We used in vitro autoradiography with [3H]MK-801, [3H]glycine, D[3H]aspartate, and [3H]muscimol to label N-methyl-D-aspartate (NMDA) receptors, glycine modulatory sites, glutamate transport sites, and gamma-aminobutyric acid-A (GABA) receptors, respectively. Rolipram (0.01 or 0.1 mg/kg, per os) or its vehicle (distilled water) was administered once a day for 4 weeks. The highest binding of [3H]MK-801, [3H]glycine, and D-[3H]aspartate was seen in the hippocampus in vehicle-treated rats. No significant differences in these binding activities were seen between young and aged rat brains. [3H]Muscimol binding was the highest in the cerebellum, and decreased in many brain regions in aged rats. The chronic rolipram treatment resulted in (1) an increase in [3H]MK-801 binding in the dentate gyrus in both young and aged rats, (2) remarkable reductions in D-[3H]aspartate binding in many regions of both young and aged rats, and (3) no or minimal changes in [3H]glycine and [3H]muscimol binding. These results suggest that the chronic rolipram treatment modifies the excitatory amino acid neurotransmission system.