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The contribution of tryptamine to the behavioural effects of l-tryptophan in tranylcypromine-treated rats

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Abstract

Rats pretreated with the monoamine oxidase inhibitor tranylcypromine and given l-tryptophan develop a characteristic behavioural syndrome. A comparison of the behavioural effects of tranylcypromine plus l-tryptophan (50 and 100 mg/kg) showed a small increase in locomotor activity and a greater increase in the behavioural score with the higher dose. This was associated with a proportionately smaller increase in brain 5-hydroxytryptamine (5-HT) than in brain tryptamine and no change in spinal cord 5-HT. Tryptamine (1–5 mg/kg) in the presence of tranylcypromine produced behavioural effects very similar to those occurring when l-tryptophan is given to tranylcypromine-pretreated rats. Increasing brain tryptamine, by the injection of tryptamine (0.75 mg/kg), enhanced the behavioural effects of tranylcypromine plus l-tryptophan (50 mg/kg) without altering brain 5-HT. Para-chlorophenylalanine pretreatment, which reduced brain 5-HT, prevented the behavioural effects of tryptamine. Inhibition of peripheral decarboxylase with R04-4602 (50 mg/kg) reduced brain tryptamine and did not alter brain 5-HT, but reduced the locomotor activity and the behavioural score of rats given tranylcypromine and l-tryptophan (100 mg/kg). The results suggest that brain tryptamine changes are partly responsible for the behavioural effects of tranylcypromine plus l-tryptophan and that some of this tryptamine is of extracerebral origin.

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Authors and Affiliations

  1. Deparment of Neurochemistry, Institute of Neurology, Queen Square, WC1N 3BG, London, UK

    C. A. Marsden & G. Curzon

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  1. C. A. Marsden
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  2. G. Curzon
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Marsden, C.A., Curzon, G. The contribution of tryptamine to the behavioural effects of l-tryptophan in tranylcypromine-treated rats. Psychopharmacology 57, 71–76 (1978). https://doi.org/10.1007/BF00426960

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  • DOI: https://doi.org/10.1007/BF00426960

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