Effects of the partial glycine agonist D-cycloserine on cognitive functioning in chronic low dose MPTP-treated monkeys.

D-Cycloserine, a partial agonist at the glycine recognition site of the N-methyl-D-aspartate (NMDA) receptor complex, has been shown to facilitate certain forms of memory formation and to improve visual recognition memory in normal monkeys. In the present study, the effects of D-cycloserine on spatial short-term memory deficits in monkeys induced by chronic low-dose 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) administration were examined. Chronic low-dose MPTP administration resulted in deficits in the performance of a variable delayed-response task (VDR). Single administration of D-cycloserine (320 or 1000 microgram/kg) significantly improved the performance on this task. High-dose D-cycloserine (8000 microgram/kg) or MK-801 (10-32 microgram/kg) administration had no effects on delayed-response performance but impaired performance on a visual discrimination (VD) task that was not adversely affected by MPTP administration. These results show that at low doses, D-cycloserine has cognition-enhancing properties in this model of early Parkinsonism.