Tranylcypromine Stereoisomers, Monoaminergic Neurotransmission and Behavior. A Minireview

Studies on the effects of the d- and l-stereoisomers of tranylcypromine on locomotor activity, aggressive behavior, hindlimb reflexes, head twitches and behaviors produced by reserpine in rats are reviewed. The d-isomer is found to produce stereotypic behavior and head twitches, to enhance extensor hindlimb reflexes, and to alter effects of reserpine on locomotor activity. The l-isomer is shown to enhance vertical and horizontal locomotor activity and to cause aggressive behavior, but failed to influence hindlimb reflexes, effects of reserpine, or to produce head twitches. Biochemical and pharmacological studies suggest that the d-isomer influences mainly tryptaminergic neurotransmission while the l-isomer affects primarily catecholaminergic neurotransmission. It is concluded that tranylcypromine stereoisomers have stereoselective effects on behavior and monoaminergic neurotransmission. The implications of the findings for the notion that the antidepressant effects of tranylcypromine are due to inhibition of MAO are briefly discussed.