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Acquisition of a behavioral response motivated by shock was enhanced in rats chronically treated with yeast ribonucleic acid, and resistance to extinction was greater in rats so treated than in controls. This extends the role of ribonucleic acid to include a behavioral effect in laboratory mammals treated with a purified preparation from yeast.

Monoamine oxidase inhibitors markedly enhance the oral pressor potency of tyramine by preventing it from being destroyed by the monoamine oxidase normally present in liver and intestine. Since certain types of cheese contain high concentrations of tyramine, they should not be eaten by patients during treatment with a monoamine oxidase inhibitor.

Tranylcypromine was compared to trifluoperazine in a number of pharmacological test procedures. Both compounds were effective in producing catalepsy, a selective blockade of the conditioned stimulus, and potentiation of hexobarbital-induced sleep. Unlike trifluoperazine, tranylcypromine was very effective as a tryptamine potentiator, a reflection of its activity as an in vivo inhibitor of the enzyme monoamine oxidase. Tranylcypromine was ineffective in producing any appreciable decrease in spontaneous motor activity at doses up to 20 mg/kg, whereas the DD50 for trifluoperazine was 1.1 mg/kg.

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