Effects of exogenous melatonin and photoperiod on sexual maturation in pullets

Effects of 6-methoxybenzoxazolinone (6-MBOA) on animals: state of knowledge and open questions

6-methoxybenzoxazolinone (6-MBOA) is a secondary plant metabolite predominantly found in monocotyledonous plants, especially Gramineae. In damaged tissue, 2-β-D-glucopyranosyloxy-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA-Glc) is hydrolyzed to DIMBOA, which spontaneously decomposes into 6-MBOA. It is commonly detected in plants consumed by voles and livestock and can also be present in cereal-based products. Discovered in 1955, this compound is renowned for its ability to trigger animal reproduction. However, there is a lack of research on its functional and mechanistic properties, leaving much of their potential unexplored. This review aimed to comprehensively summarize the effects of 6-MBOA on animal reproduction and human health, as well as its defensive role against herbivores. Studies have shown that 6-MBOA effectively inhibits the digestion, development, growth, and reproduction of insects. 6-MBOA may act as a partial agonist of melatonin and exert a regulatory role in mammalian reproduction, resulting in either promoting or inhibiting effects. 6-MBOA has been theorized to possess anti-tumor, anti-AIDS, anti-anxiety, and weight-loss effects in humans. However, insufficient attention has been paid to its defense properties against mammalian herbivores, and the mechanisms underlying its effects on mammalian reproduction remain unclear. In addition, research on its impact on human health is still in its preliminary stages. The review emphasizes the need for further systematic and comprehensive research on 6-MBOA to fully understand its diverse functions. Elucidating the effects of 6-MBOA on animal reproduction, adaptation, and human health would advance our understanding of plant-herbivore coevolution and the influence of environmental factors on animal population dynamics. Furthermore, this knowledge could potentially promote its application in human health and animal husbandry.

Effects of Duodenal 5-Hydroxytryptophan Perfusion on Melatonin Synthesis in GI Tract of Sheep

The purpose of this study is to investigate the potential effects of 5-hydroxytryptophan (5-HTP) duodenal perfusion on melatonin (MT) synthesis in the gastrointestinal (GI) tract of sheep. 5-hydroxytryptophan is a precursor in the melatonin synthetic pathway. The results showed that this method significantly increased melatonin production in the mucosa of all segments in GI tract including duodenum, jejunum, ileum, cecum and colon. The highest melatonin level was identified in the colon and this indicates that the microbiota located in the colon may also participate in the melatonin production. In addition, portion of the melatonin generated by the GI tract can pass the liver metabolism and enters the circulation via portal vein. The current study provides further evidence to support that GI tract is the major site for melatonin synthesis and the GI melatonin also contributes to the circulatory melatonin level since plasma melatonin concentrations in 5-HTP treated groups were significantly higher than those in the control group. In conclusion, the results show that 10–50 mg of 5-HTP flowing into the duodenum within 6 h effectively improve the production of melatonin in the GI tract and melatonin concentration in sheep blood circulation during the day.

Prolonging photoperiod promotes testosterone synthesis of Leydig cells by directly targeting local melatonin system in rooster testes

The study investigated the effects of prolonging photoperiod on the synthesis of testosterone and melatonin in roosters, and the effect of melatonin on testosterone synthesis in rooster Leydig cells as well as its molecular mechanisms. We randomly divided one hundred and twenty 20-week-old roosters into three groups and provided 6, 12.5 and 16 h light, respectively. The results showed that prolonging photoperiod promoted testosterone synthesis, decreased melatonin production, and inhibited the expression of melatonin membrane receptors MEL1A, MEL1B, MEL1C, and aralkylamine n-acetyltransferase (AANAT) in rooster testes. Subsequently, rooster Leydig cells were isolated and treated with 0, 0.1, 1, 10, and 100 ng/mL melatonin for 36 h. The results suggested that melatonin inhibited testosterone synthesis in rooster Leydig cells, and silencing MEL1A and MEL1B relieved the inhibition of melatonin on testosterone synthesis. Additionally, melatonin reduced the intracellular cyclic adenosine monophosphate (cAMP) level and the phosphorylation level of cAMP-response element binding protein (CREB), and CREB overexpression alleviated the inhibition of melatonin on testosterone synthesis. Furthermore, pretreatment with cAMP activator forskolin or protein kinase A (PKA) activator 8-bromo-cAMP blocked the inhibition of melatonin on CREB phosphorylation and testosterone synthesis. These results indicated that prolonging photoperiod promoted testosterone synthesis associated with the decrease in melatonin production and membrane receptors and biosynthetic enzyme of melatonin in rooster testes, and melatonin inhibited testosterone synthesis of rooster Leydig cells by inhibiting the cAMP/PKA/CREB pathway via MEL1A and MEL1B. This may be evidence that prolonging photoperiod could promote testosterone synthesis through the inhibition of the local melatonin pathway in rooster testes.

BMAL1 but not CLOCK is associated with monochromatic green light-induced circadian rhythm of melatonin in chick pinealocytes

The avian pineal gland, an independent circadian oscillator, receives external photic cues and translates them for the rhythmical synthesis of melatonin. Our previous study found that monochromatic green light could increase the secretion of melatonin and expression of CLOCK and BMAL1 in chick pinealocytes. This study further investigated the role of BMAL1 and CLOCK in monochromatic green light-induced melatonin secretion in chick pinealocytes using siRNAs interference and overexpression techniques. The results showed that si-BMAL1 destroyed the circadian rhythms of AANAT and melatonin, along with the disruption of the expression of all the seven clock genes, except CRY1. Furthermore, overexpression of BMAL1 also disturbed the circadian rhythms of AANAT and melatonin, in addition to causing arrhythmic expression of BMAL1 and CRY1/2, but had no effect on the circadian rhythms of CLOCK, BMAL2 and PER2/3. The knockdown or overexpression of CLOCK had no impact on the circadian rhythms of AANAT, melatonin, BMAL1 and PER2, but it significantly deregulated the circadian rhythms of CLOCK, BMAL2, CRY1/2 and PER3. These results suggested that BMAL1 rather than CLOCK plays a critical role in the regulation of monochromatic green light-induced melatonin rhythm synthesis in chicken pinealocytes. Moreover, both knockdown and overexpression of BMAL1 could change the expression levels of CRY2, it indicated CRY2 may be involved in the BMAL1 pathway by modulating the circadian rhythms of AANAT and melatonin.

Melatonin Administration Methods for Research in Mammals and Birds

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Melatonin in plant signalling and behaviour

Melatonin is an indoleamine neurotransmitter that has recently become well established as an important multi-functional signalling molecule in plants. These signals have been found to induce several important physiological responses that may be interpreted as behaviours. The diverse processes in which melatonin has been implicated in plants have expanded far beyond the traditional roles for which it has been implicated in mammals, which include sleep, tropisms and reproduction. These functions, however, appear to also be important melatonin mediated processes in plants, though the mechanisms underlying these functions have yet to be fully elucidated. Mediation or redirection of plant physiological processes induced by melatonin can be summarised as a series of behaviours including, among others: herbivore defence, avoidance of undesirable circumstances or attraction to opportune conditions, problem solving and response to environmental stimulus. As the mechanisms of melatonin action are elucidated, its involvement in plant growth, development and behaviour is likely to expand beyond the aspects discussed in this review and hold promise for applications in diverse fundamental and applied plant sciences including conservation, cryopreservation, morphogenesis, industrial agriculture and natural health products.

Melatonin modulates monochromatic light-induced melatonin receptor expression in the hypothalamus of chicks

To study the mechanism of the effect of monochromatic light on physiological function in chicken, a total of 192 newly hatched chicks were randomly divided into intact, sham-operated and pinealectomy groups then exposed to white light (WL), red light (RL), green light (GL) and blue light (BL) using a light-emitting diode (LED) system for two weeks. At P14, the hypothalami were immediately collected for immunohistochemical staining of melatonin receptor subtypes (Mel1a and Mel1b) and detection of Mel1a and Mel1b expressions using RT-PCR and western blot. Immunohistochemical staining of the hypothalamus showed that the Mel1a-ir cells were distributed in the preoptic area (POA), nucleus preopticus periventricularis (POP) and suprachiasmatic nuclei (SCN), and the Mel1b-ir cells were presented in the POA and SCN. Analysis of RT-PCR and western blot showed that the mRNA and protein levels of Mel1a and Mel1b in the hypothalamus of chick exposed to GL were increased by 10.7-29.3%, 9.18-35.9% and 8.97-27.3% compared to those in the chicks exposed to WL (P=0.029-0.002), RL (P=0.027-0.001) and BL (P=0.038-0.007) in the intact group, respectively. After pinealectomy, however, these parameters decreased and there were no significant differences among the WL, RL, GL and BL groups. These findings suggested that melatonin plays a critical role in GL illumination-enhanced Mel1a and Mel1b expressions in the hypothalamus of chicks.