Chronic effects of monoamine oxidase-B inhibitors on the behaviour of aged mice

In order to measure the chronic effects of monoamine oxidase-B (MAO-B) inhibitors on the physical and cognitive condition of 60 aged male mice, l-deprenyl or N-methyl-N-(2-pentyl)-propargylamine (M-2-PP) were administered in drinking water (10 μg/ml/day) for 37 weeks. The spontaneous open-field locomotion, balancing ability and weight gain of the mice were assessed continuously. At the end of the study the spatial learning ability of all surviving mice was assessed in a Morris water maze. Both drug groups exhibited a reduction in spontaneous locomotion at the same rate as the control group, while there were no changes in balancing ability. The mice receiving l-deprenyl, however, performed the water maze task less well than the control group. The mice receiving l-deprenyl also gained weight at a significantly reduced rate compared to both the M-2-PP and water treated groups. A brain MAO assay indicated that MAO-B was completely inhibited by both drugs while MAO-A remained unchanged. The implications of these data on longevity studies using l-deprenyl and other MAO-B inhibitors are discussed.