Effects of selective monoamine oxidase (MAO) inhibitors on conditioned avoidance responses (CAR) of rats

Dopamine (DA) insufficiency in the ipsilateral corpus striatum produced by unilateral electrolytic lesion of the substantia nigra (SN) resulted in an impairment in rats' behavior as tested by one-way and two-way avoidance techniques. Selective MAO-A inhibitor, clorgyline (1 mg/kg sc daily for 7 days), improved the reduced learning capacity of SN lesioned animals, restored the decreased DA content in the corpus striatum, and caused significant hyperactivity as tested in the open field. At the same time the selective MAO-B inhibitor (-)deprenyl (injected the same way) proved to be ineffective. J-508, a selective MAO-B inhibitor, used in a non-selective dose (1 mg/kg), acted like clorgyline. The results support the hypothesis that in the rat nigrostriated system (but not in human beings) DA is preferentially deaminated by the A form of MAO.