Conditioned taste aversion and conditioned drinking: two independent and opposing effects of 5-hydroxytryptophan?

Four experiments were carried out to examine the effects of 5-HTP in a conditioned taste aversion (CTA) paradigm. Using two-choice tests to measure the CTA, administration of 5-HTP following consumption of a novel flavour caused aversions to saline and saccharin solutions. In single-choice tests 5-HTP reduced consumption of saccharin, sugar cubes and beef-flavoured stock cubes, but only reduced saline consumption if animals had been pretreated with the 5-HTP decarboxylase inhibitor benserazide or the 5-HT receptor antagonist xylamidine, both of which act peripherally. Benserazide did not attenuate the CTA in any experiment. The results are interpreted in terms of two competing behavioural effects of 5-HTP: a centrally-mediated CTA and a peripherally-mediated conditioned drinking response.