Acute administration of a tryptophan-free amino-acid mixture
decreases 5-ht release in rat hippocampus in vivo.
Stancampiano, Roberto, Franco Melis, Laura Sarais, Stefania Cocco,
Carla Cugusi, and Fabio Fadda.
Institute of Human Physiology, University of Cagliari, Via Porcell
4, I-09124 Cagliari, Italy
APStracts 3:0430R, 1996.
The effect of oral administration of a tryptophan-free amino-acid
mixture or the same mixture containing tryptophan (TRP) on
hippocampal serotonin (5-HT) extracellular levels was studied using
in vivo brain microdialysis of freely moving rats. During chloral
hydrate anaesthesia rats were implanted with dialysis probes in the
dorsal hippocampus, and experiments were performed 24 h later. In
vehicle treated rats the extracellular levels of 5-hydroxyindolacetic
acid (5-HIAA) and 5-HT did not change during 240 min after ingestion.
Oral administration of the TRP-free amino-acid mixture significantly
decreased basal 5-HT and 5-HIAA output 100 min after ingestion (65%
and 81% of basal value, respectively) and remained at this level for
another 140 min. The amino-acid mixture containing TRP failed to
significantly change basal extracellular levels of 5-HT, but enhanced
that of 5-HIAA by about 134%. Moreover, in rats receiving the TRP
-free amino-acid mixture the increase of hippocampal 5-HT release
induced by d-fenfluramine (206%) was smaller than that released by
the same drug in rats receiving the B mixture (271%). Thus, these
results show that removal of TRP from the balanced amino-acid mixture
decreases spontaneous and d-fenfluramine-induced release of 5-HT in
the hippocampus. In conclusion, our study supports the hypothesis
that the mood-lowering effect observed in man after ingestion of the
TRP-free amino-acid mixture is associated with diminished 5-HT
release in the brain.
Received 21 November 1995; accepted in final form 3 September
1996.
APS Manuscript Number R730-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996