Effects of tryptophan and/or acute running on extracellular 5-HT and 5-HIAA levels in the hippocampus of food-deprived rats.
The present microdialysis study has examined whether exercise-elicited increases in brain tryptophan availability (and in turn 5-HT synthesis) alter 5-HT release in the hippocampus of food-deprived rats. To this end, we compared the respective effects of acute exercise, administration of tryptophan, and the combination of both treatments, upon extracellular 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels. All rats were trained to run on a treadmill before implantation of the microdialysis probe and 24 h of food deprivation. Acute exercise (12 m/min for 1 h) increased in a time-dependent manner extracellular 5-HT levels (maximal increase: 47%), these levels returning to their baseline levels within the first hour of the recovery period. Besides, exercise-induced increases in extracellular 5-HIAA levels did not reach significance. Acute administration of a tryptophan dose (50 mg/kg i.p.) that increased extracellular 5-HIAA (but not 5-HT) levels in fed rats, increased within 60 min extracellular 5-HT levels (maximal increase: 55%) in food-deprived rats. Whereas 5-HT levels returned toward their baseline levels within the 160 min that followed tryptophan administration, extracellular 5-HIAA levels rose throughout the experiment (maximal increase: 75%). Lastly, treatment with tryptophan (60 min beforehand) before acute exercise led to marked increases in extracellular 5-HT and 5-HIAA levels (maximal increases: 100% and 83%, respectively) throughout the 240 min that followed tryptophan administration. This study indicates that exercise stimulates 5-HT release in the hippocampus of fasted rats, and that a pretreatment with tryptophan (at a dose increasing extracellular 5-HT levels) amplifies exercise-induced 5-HT release.
Meeusen
R
R
Department of Human Physiology, Vrije Universiteit Brussel, Belgium.
Thorré
K
K
Chaouloff
F
F
Sarre
S
S
De Meirleir
K
K
Ebinger
G
G
Michotte
Y
Y
D000818:Animals; D005508:Food Deprivation / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000494:pharmacology*
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan