Abstract
We studied the effects of adverse conditions such as constant light (LL) on the circadian rhythm of malate (MDH, EC 1.1.1.37) and lactate (LDH, EC 1.1.1.27) dehydrogenase activities of the testes of male Wistar rats on postnatal day 28 (PN28), anxiety-like behavior (elevated plus-maze test) at PN60 and sexual behavior at PN120. The rats were assigned to mother groups on day 10 of pregnancy: control (12-h light/dark), LL (light from day 10 to 21 of pregnancy), and LL+Mel (LL and sc injection to the mothers of a daily dose of melatonin, 1 mg/kg body weight at circadian time 12, from day 17 to 21 of pregnancy). LL offspring did not show circadian rhythms of MDH (N = 62) and LDH (N = 63) activities (cosinor and ANOVA-LSD Fisher). They presented a 44.7% decrease in open-arm entries and a 67.9% decrease in time (plus-maze test, N = 15, P < 0.001, Mann-Whitney U-test and Kruskal-Wallis test), an increase in mounting (94.4%), intromission (94.5%) and ejaculation (56.6%) latencies (N = 12, P < 0.01, Mann-Whitney U-test and Kruskal-Wallis test) and lower numbers of these events (61, 59 and 73%, respectively; P < 0.01, N = 12) compared to controls. The offspring of the LL+Mel group presented MDH and LDH circadian rhythms (P < 0.05, N = 50, cosinor and ANOVA-LSD Fisher), anxiety-like and sexual behaviors similar to control. These findings supported the importance of the melatonin signal and provide evidence for the protective effects of hormones on maternal programming during gestation. This protective action of melatonin is probably related to its entrainment capacity, favoring internal coupling of the fetal multioscillatory system.
Highlights
Melatonin is a multifunctional indolamine synthesized and secreted by the pineal gland and other organs [1]
The fetus, whose pineal gland does not synthesize melatonin, is exposed to the maternal melatonin rhythm that begins to increase from the 12th day of gestation in rats [8]
The present study showed, for the first time, that constant light during gestation induces an early disruption of daily oscillation of malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) in offspring rat testes together with long-term effects on anxiogenic and copulatory behavior patterns
Summary
Melatonin is a multifunctional indolamine synthesized and secreted by the pineal gland and other organs [1]. The fetus, whose pineal gland does not synthesize melatonin, is exposed to the maternal melatonin rhythm that begins to increase from the 12th day of gestation in rats [8]. Hormone binding sites are identified in the suprachiasmatic nucleus (SCN) of a fetus from the 18th day of gestation [9]. This melatonin path, which mediates interactions between maternal and fetal physiological functions, has been explored mostly in fetal and neonatal circadian rhythms [10,11,12]
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