Backward walking induced by L-5-hydroxytryptophan in mice.

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Abstract
An i.p. administration of large doses of L-5-hydroxytryptophan (L-5HTP) induced dose-dependently a behavior characterized by backward walking in mice. D-5-hydroxytryptophan (D-5HTP) and L-DOPA in the same doses failed to induce such behavior. The backward walking induced by L-5HTP was blocked by a decarboxylase inhibitor, DL-.alpha.-methyldopa, but was potentiated by a monoamine oxidase inhibitor (MAOI), tranylcypromine or pargyline. An intracerebral injection of L-5-hydroxytryptamine (5-HT) induced a similar backward walking which was potentiated by a MAOI. The backward walking induced by L-5HTP was completely inhibited by 5-HT and dopamine (DA) receptor blockers, but was not inhibited by .alpha.- or .beta.-adrenergic blocker, antihistamine or anticholinergic drug. Zimelidine and clomipramine, 5-HT uptake inhibitors, potentiated the backward walking, while desipramine had no effect. Excess amounts of 5-HT formed from L-5HTP produced the backward walking by directly stimulating the central 5-HT receptors, and DA is involved in the behavior. This behavior may serve as a good model to assess the central serotonergic activity of drugs.

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