Differential improvement in memory-related task performance with nicotine by aged male and female rhesus monkeys

Central nicotine acetylcholine receptors have been targeted for the development of novel treatments for memory deficits in Alzheimer's disease (AD) and other neurodegenerative disorders. Nicotine itself has been shown to improve memory related task performance in aged animals and in AD patients. Administration of nicotinic receptor agonists to laboratory animals, and the effects of cigarette smoking in humans attributed to nicotine, have in many instances been shown to exert sexually dimorphic actions. Low doses (2.5-20 μg/kg, intramuscularly) of nicotine have been shown to improve the performance of an automated delayed matching-to-sample (DMTS) task in aged rhesus monkeys. The purpose of this study was to determine whether aged females receive the same level of benefit to the positive mnemonic action of nicotine as do males. In this study six male (21.7 ± 1.2 years) and seven female (22.5 ± 0.9 years) rhesus monkeys each received an ascending series of four doses of nicotine over 5 weeks. Most control parameters were similar between the two sexes, although task latencies were longer and more variable in the female subjects. The males maintained a significant improvement in task performance over the entire nicotine dose range. This level of improvement extended to 24 h after nicotine administration. Task accuracy by females appeared to improve only after they received the two higher doses of nicotine, and their responses exhibited considerable variability over the entire dose range. However, in calculating an individualized 'Best Dose', males and females exhibited a similar level of task improvement (15-30% above baseline). Therefore, aged female subjects may require a greater level of individualized treatment and perhaps higher doses of nicotinic agonists to achieve the maximal mnemonic benefit.