Effects of pinealectomy and melatonin treatments on serotonin uptake and release from synaptosomes of rat hypothalamic regions |
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Authors: | J M Miguez F J Martin Dr M Aldegunde |
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Institution: | (1) Laboratorio de Fisioloxia Animal, Facultade de Bioloxía, Universidade de Santiago de Compostela, 15706 Santiago de Compostela, Spain |
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Abstract: | 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. |
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Keywords: | Pinealectomy melatonin serotonin uptake and release synaptosomes hypothalamic regions |
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