Behavioral effects of 5-hydroxy-N-acetyltryptophan, a putative synthetic precursor of N-acetylserotonin

1. Adult male rats were injected with either 5-hydroxy-N-acetyltryptophan (5-OHNAT), a synthetic putative precursor of N-acetylserotonin, or 5-hydroxytryptophan (5-HTP), the serotonin precursor, and behavioral effects were observed. Pretreatment consisted of carbidopa and nialamide. 2. The behavioral effects of systemic injections of 5-OHNAT and 5-HTP were qualitatively similar i.e. head weaving, forepaw treading, etc., but the effect of 5-OHNAT was appreciably delayed in onset. 3. 5-OHNAT loading may cause an increase in central nervous system 5-HT via initial deacetylation to 5-HTP. Alternatively, 5-OHNAT may cause a delayed increase in brain NAS and the "serotonin syndrome" may reflect increased conversion of 5-HT to NAS.