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Pharmacological enhancement of long-term memory retention in old mice.

This study examined memory retention deficits in 24-month-old mice as compared to 4-month-old mice and if they were related to an altered functional state of neurotransmitters or hormones that modulate memory. We administered to 24-month-old C57BL/6Nnia mice pharmacological compounds known to improve retention in young mice. Eleven of the pharmacological agents improved retention in old mice at the dose previously shown to be optimal in young mice. Clonidine and ST 587, the two alpha noradrenergic agonists tested, failed to enhance retention at the optimum dose for young mice. A dose response study with clonidine found that a lower dose (1 mg/kg) improved retention in old mice rather than the optimal dose (3 mg/kg) for young mice. These data suggest that memory retention in old C57BL/6Nnia mice is similar to that of young mice, with the exception of alpha noradrenergic receptors.