The effects of aging and dopaminergic inhibition on large scale maze learning in rhesus monkeys

Abstract

Studies have shown that both aging and dopaminergic dysfunction affected spatial learning and memory. Systematic dopaminergic inhibition, by dopamine receptor (DR) antagonist treatment, impaired spatial delayed-response (SDR) performance, which mostly requires self/body centered egocentric reference frame, in rhesus monkeys. However, the influence of DR blocking on large scale maze learning, which mainly involves world centered allocentric reference frame, remains unclear. Moreover, the effects of aging on the process also remain unknown. Present study investigated the issues, using large scale mazes composed of 8 maze units. Maze No. 1 was used for adaptation and training. Mazes No. 2-4 were used to investigate influence of aging, by comparing learning performance between young and aged rhesus monkeys. Mazes No. 5-8 were used to investigate the effects of DR antagonist treatment, SKF-83566 (0.02, 0.2\u2009mg/kg) and haloperidol (0.001, 0.01\u2009mg/kg). The result showed similar learning performance between young and aged monkeys in mazes No. 2-4. In mazes No. 5-8, we also found similar learning performance after acute DR antagonist injection, compared with pre-treatment baseline performance in mazes No. 2-4, in both young and aged groups. The result showed similar maze learning performance between young and aged monkeys in mazes (No. 2-4), suggesting no significant influence of aging on allocentric spatial learning. We also found similar maze performance in both groups, after dopamine receptor antagonist treatment in mazes (No. 5-8) compared with pre-treatment baseline performance in mazes (No. 2-4), suggesting no significant influence of dopaminergic inhibition on allocentric spatial learning. Together, the present study potentially suggested insensitivity of allocentric spatial learning to cognitive aging and acute systematic dopaminergic inhibition.