Abstract
The main objective of this study was to analyze the effects of sex, ovariectomy (Ovx) and orchidectomy (Orx) on antidepressant and anxiolytic effect of melatonin in forced swimming test, open field test and elevated plus maze test. Initially, 4 mg/kg of melatonin was daily administered, at 4:00 pm, to intact male and female rats during 8 weeks. Our results have shown that the effect of chronic injection of Mel is sex dependent in the three behaviors tests. Females rats have responded better than males in behavior test study after administration of melatonin, this difference between the sexes may be related to the action of sex hormones (androgens and estrogens) on behavior in males as well as in females. Secondly, to determine the possible interaction between Melatonin and steroid hormones, Ovx/sham female received Mel at dose of 4mg/kg alone or NaCl (0.9%) alone, and Orx/sham male received Mel at dose of 4 mg/kg alone or NaCl (0.9%) alone daily and during 8 weeks of treatment at 4:00 pm. All animals were tested in the open-field test, elevated plus maze test for anxiety behavior study, and forced swimming test for depression behavior study. Results revealed that Mel exerts an anxiolytic and antidepressant effects in the orchidectomized males and in intact females, confirming that the suppression of androgens by orchidectomy improved anxiolytic and antidepressant effects of melatonin in males. However in females, the suppression of estrogen by ovariectomy masked the antidepressant and anxiolytic effects of melatonin. Our results confirmed that the antidepressant and anxiolytic effects of melatonin are linked to sex hormones.
Highlights
In the rat, rhythmic melatonin production is driven by a circadian rhythm of the activity of pineal N-acetyltransferase (NAT) which synthesizes the melatonin precursor N-acetylserotonin [1]
The main purpose of the current study was to investigate the influence of gonadectomy on antidepressant and anxiolytic effects of melatonin in male and female rats in forced-swim behavior, Elevated place maze, and open field test, in order to demonstrate an eventual implication of sexual hormones
The aim of this study was to analyze the influence of gonadectomy on antidepressant and anxiolytic effects of melatonin in male and female rats
Summary
Rhythmic melatonin production is driven by a circadian rhythm of the activity of pineal N-acetyltransferase (NAT) which synthesizes the melatonin precursor N-acetylserotonin [1]. Photic information is conveyed to the SCN by a direct retinal projection, the retinohypothalamic tract, and, to a lesser extent, by other pathways especially by the geniculohypothalamic tract [3,4] In the rat, these photic inputs terminate mostly in the ventrolateral (vl) or ventral part of the SCN [4,5]. Melatonin is released directly into general circulation to establish its endocrine function on blood glucose, appetite, and sleep. In addition to these functions, melatonin seems to exert psychotropic effects in rodents, such as sedative activeties, analgesic, anticonvulsionants, anxiolytic and antidepressant [7,8].
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