Extracellular hypothalamic serotonin and plasma amino acids in response to sequential carbohydrate and protein meals

Nutr Neurosci. 2003 Apr;6(2):117-24. doi: 10.1080/1028415031000079676.


In previous studies, we showed that carbohydrate and protein ingestion, respectively, increased and decreased hypothalamic extracellular serotonin and the plasma ratio tryptophan over its competitor amino acids (Trp/LNAAs), reflecting serotonin synthesis. Serotonin levels returned towards baseline 2 h after either meal while the ratio remained altered. The question addressed is the ability of serotonin to respond expectedly to a second meal of the alternate nutrient. Rats were fed with sequential meals of either carbohydrates first and then casein 2 h later or in reverse order. Hypothalamic serotonin was measured using microdialysis. Permanent blood sampling allowed to track in parallel plasma amino acids. A carbohydrate meal increased hypothalamic serotonin, so did a subsequent casein meal. Conversely, following a casein meal that reduced serotonin, a carbohydrate meal also decreased it. The plasma ratio Trp/LNAAs was enhanced by a carbohydrate meal and remained high for 2h. A subsequent casein meal reversed this change but the ratio remained higher than basal values. A first casein meal reduced the ratio that was not increased again by a subsequent carbohydrate meal. It is obvious that ingestion of specific nutrients induce long-lasting metabolic and neurochemical variations that prevent subsequent changes to occur. The lack of expected changes to a second meal addresses again the hypothesis of alternate appetites for carbohydrates and proteins driven by serotonin changes.

MeSH terms

  • Amino Acids / blood*
  • Animals
  • Caseins / administration & dosage
  • Dietary Carbohydrates / administration & dosage*
  • Dietary Proteins / administration & dosage*
  • Extracellular Space / chemistry
  • Food
  • Hypothalamus / metabolism*
  • Kinetics
  • Male
  • Rats
  • Rats, Wistar
  • Serotonin / analysis
  • Serotonin / metabolism*
  • Tryptophan / blood


  • Amino Acids
  • Caseins
  • Dietary Carbohydrates
  • Dietary Proteins
  • Serotonin
  • Tryptophan