Effect of monoamineoxidase inhibitors on 5‐hydroxytryptamine output from perfused cerebral ventricles of anaesthetized cats

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Abstract
1 . In cats anaesthetized with pentobarbitone sodium, intraperitoneal injections of four inhibitors of monoamine oxidase (MAO) were shown to increase the 5-hydroxytryptamine (5-HT) in the effluent from the perfused cerebral ventricles. 2 . Weight for weight, tranylcypromine was found to be about twice as potent as pheniprazine, eight times as potent as nialamide and sixty times as potent as pargyline. 3 . The effect of tranylcypromine was also examined after reserpine had been injected into the cerebral ventricles or after p-chlorophenylalanine, given intraperitoneally. In both conditions tranylcypromine retained its ability to increase the 5-HT output from the perfused cerebral ventricle, but the effect was attenuated, more after p-chlorophenylalanine than after reserpine. 4 . Evidence is put forward that in both conditions the brain is not completely depleted of its 5-HT, but that the 5-HT is only reduced, more after p-chlorophenylalanine than after reserpine.