Age-induced differentiation of morphine's effect on cyclic nucleotide metabolism

Male ICR mice, immature (25 days old), mature adult (3 months old) and aged (22 months old), were injected with morphine sulfate (10 mg/kg, SC) or were implanted with morphine pellets (75 mg). Age-matched controls received saline injections or placebo pellets. One hour after injections and 72 hours after pellet implantation (when tolerance to morphine had occurred), the mice were decapitated and the frontal cortex and cerebellum were removed. Basal activities of adenylate cyclase, guanylate cyclase, cyclic AMP phosphodiesterase and cyclic GMP phosphodiesterase were determined in both brain regions. Results showed that there are age- and region-differentiated effects of morphine on these enzymes.