Effects of single doses and daily melatonin treatments on serotonin metabolism in rat brain regions.
The acute effects of two doses (0.5 and 1 mg/kg) of melatonin on the levels of tryptophan, serotonin, and 5-hydroxyindoleacetic acid in several rat brain regions were studied. Tryptophan content in the brain regions was unchanged by the treatments. Melatonin at a dosage of 0.5 mg/kg increased medial hypothalamic serotonin levels at 60 and 90 min after the injection. However, the dose of 1 mg/kg increased the levels of this amine or its metabolite in the preoptic area-anterior hypothalamus, medial and posterior hypothalamus, amygdala, and midbrain. These results suggest a specific regional sensitivity to melatonin as well as a dose-dependent response. The stimulatory melatonin effect on the serotoninergic system was also observed after a daily treatment with this hormone (0.5 mg/kg, twice daily during 10 days) in both intact or pinealectomized rats. In intact rats, melatonin treatment increased the levels of 5-hydroxyindole-3-acetic acid in the preoptic area-anterior hypothalamus and medial hypothalamus, while in pinealectomized rats melatonin increased the serotonin content in the medial hypothalamic region. The data support the idea that melatonin has a selective action on serotonin metabolism in regions that contain serotoninergic terminals, especially at medial hypothalamic level.
Miguez
J M
JM
Laboratorio de Fisioloxía Animal, Facultade de Bioloxía, Universidade de Santiago de Compostela, Spain.
Martin
F J
FJ
Aldegunde
M
M
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D007279:Injections, Subcutaneous; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D010870:Pineal Gland / Q000502:physiology / Q000601:surgery; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan; D008550:Melatonin