Effects of pinealectomy and melatonin treatments on serotonin uptake and release from synaptosomes of rat hypothalamic regions.
This study examined the effects induced by long-term pinealectomy, daily melatonin treatment to pinealectomized and intact rats, and a single melatonin injection on [14C]-serotonin (5-HT) uptake and release from synaptosomes obtained of hypothalamic regions. Pinealectomy inhibited the accumulation of labeled 5-HT by synaptosomes of the preoptic area-anterior hypothalamus (POA-AH), but it failed to alter the [K+]-evoked 5-HT release. Melatonin treatment for 10 consecutive days to pinealectomized rats restored 5-HT uptake in POA-AH, and also increased 5-HT release in medial and posterior hypothalamus. These results suggest that pineal melatonin plays a stimulatory role on the serotoninergic terminals of the hypothalamus. Moreover, when daily melatonin treatment was administered to intact rats a significant increase in 5-HT uptake activity by synaptosomes of all the hypothalamic regions was observed, but 5-HT release was unaffected. In contrast, a single melatonin injection induced a significant decrease in 5-HT release from synaptosomes of the POA-AH was observed. The results suggest the existence of a differential sensitivity in the mechanisms mediating melatonin actions on 5-HT uptake/release, which depends on the presence of the pineal gland in the animals and on the frequency of the treatments with the pineal hormone.
Miguez
J M
JM
Laboratorio de Fisioloxía Animal, Universidade de Santiago de Compostela, Spain.
Martin
F J
FJ
Aldegunde
M
M
D000818:Animals; D004334:Drug Administration Schedule; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D066298:In Vitro Techniques; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D010870:Pineal Gland / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism
D012701:Serotonin; D008550:Melatonin