Chronic L-deprenyl or L-amphetamine: Equal cognitive enhancement, unequal MAO inhibition

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Abstract

The effect of chronic (4 month), subcutaneous injections of saline, L-deprenyl (0.25 mg/kg), or L-amphetamine (0.25 mg/kg) on the acquisition of a learned spatial habit in a modified Morris Water Maze investigated in middle aged rats. Injections, given three times weekly starting at 6 months of age, were continued during behavioral testing, which occurred at 10 months of age. The cognitive performance of the middle aged rats was compared to that of 2-month-old control rats. Twenty-four hours after the last behavioral test, the rats were sacrificed and their brains were removed, dissected, and frozen in liquid nitrogen. The activities of MAO-A and MAO-B in the lateral cortex were determined. Results indicate that rats in the L-deprenyl group, the L-amphetamine group, and the young control group all learned the water maze task equally rapidly and significantly faster than rats in the saline group. MAO-A did not differ among the saline, amphetamine, and young control rats, but MAO-B was significantly higher in the middle aged saline and L-amphetamine rats than in the young controls. Both MAO-B and MAO-B activities were significantly lower in the L-deprenyl group than in the other three groups. This indicates that low-dose L-deprenyl can also inhibit MAO-A following chronic SC adminitration. Moreover, the improved cognitive performance produced by L-deprenyl may not be due to its ability to inhibit MAO-B, but rather to some other effect such as the activation of growth factors. It remains to be determined whether this mechanism is produced by, shared with, or independent from deprenyl's amphetamine metabolites.

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