Melatonin does not produce sedation in rats: A chronobiological study

Melatonin Ameliorates Organellar Calcium Homeostasis, Improving Endoplasmic Reticulum Stress-Mediated Apoptosis in the Vastus Lateralis Muscle of Both Sexes of Obese Diabetic Rats

Endoplasmic reticulum (ER) stress is a crucial factor in the progression of obesity-related type 2 diabetes (diabesity), contributing to skeletal muscle (SKM) dysfunction, calcium imbalance, metabolic inflexibility, and muscle atrophy. The ER and mitochondria together regulate intracellular calcium levels, and melatonin, a natural compound with antioxidant properties, may alleviate these challenges. Our previous research showed that melatonin raises intracellular calcium and preserves muscle structure by enhancing mitochondrial function in obese diabetic rats. This study further explores melatonin's potential to reduce ER stress in the vastus lateralis (VL) muscle by modulating the unfolded protein response (UPR) and restoring calcium levels disrupted by diabesity. Five-week-old Zücker diabetic fatty (ZDF) rats and lean littermates of both sexes were divided into control and melatonin-treated groups (10 mg/kg/day for 12 weeks). Flame atomic absorption spectrometry results showed that melatonin restored VL intraorganellar calcium homeostasis, increasing calcium levels in mitochondria and reducing them in the ER by raising the activity and expression of calcium transporters in both sexes of ZDF rats. Melatonin also decreased ER stress markers (GRP78, ATF6, IRE1α, and PERK) and reduced pro-apoptosis markers (Bax, Bak, P-JNK, cleaved caspase 3 and 9) while increasing Bcl2 levels and melatonin receptor 2 (MT2) expression. These findings suggest that melatonin may protect against muscle atrophy in obese and diabetic conditions by mitigating ER stress and calcium imbalance, highlighting its therapeutic potential.

Melatonin mitigates vincristine-induced peripheral neuropathy by inhibiting TNF-α/astrocytes/microglial cells activation in the spinal cord of rats, while preserving vincristine's chemotherapeutic efficacy in lymphoma cells

Vincristine (VCR), an anti-tubulin chemotherapy agent, is known to cause peripheral and central nerve damage, inducing severe chemotherapy-induced peripheral neuropathy (CIPN). Although melatonin has been recently recognized for its potential anti-neuropathic effects, its efficacy in countering VCR-induced neuropathy remains unclear. This study examines the neuroprotective potential of melatonin against VCR-induced neuropathy using a rat model. Neuropathic pain was induced through 10 VCR injections (0.1 mg/kg/day i.p.), administered in two five-day cycles with a two-day break. Melatonin treatment started two days before VCR administration and continued daily throughout the experiment. Rats were assigned to five groups: control, VCR, and three melatonin-treated groups receiving VCR with melatonin (5, 10, or 20 mg/kg/day i.p.). We assessed mechanical (von-Frey and Randall-Selitto tests) and thermal (hot-plate and tail-flick tests) hyperalgesia, motor coordination (rotarod test), and sciatic nerve conduction velocity (NCV). Changes in body weight, spinal cord histopathology (H&E), and proinflammatory markers (TNF-α, IL-1β, and IL-6), reactive astrocytes (GFAP) and microglial cells (IBA-1) were also assessed, as well as spinal cord degeneration (Nissl stain) and demyelination (LFB stain and MBP). Finally, the effect of melatonin on the cytotoxic activity of VCR against EL4 lymphoma cells was assessed using an MTT assay. Our results indicated that melatonin coadministration with VCR preserved spinal cord architecture, elevated nociceptive thresholds, improved motor coordination, enhanced NCV, and maintained normal body weight gain. Melatonin also reduced inflammation, decreased reactive astrocytes and microglia, and prevented neurodegeneration and demyelination in the spinal cord. Importantly, melatonin did not affect VCR's cytotoxic activity in cancer cells.

Keep Your Mask On: The Benefits of Masking for Behavior and the Contributions of Aging and Disease on Dysfunctional Masking Pathways

Environmental cues (e.g., light-dark cycle) have an immediate and direct effect on behavior, but these cues are also capable of “masking” the expression of the circadian pacemaker, depending on the type of cue presented, the time-of-day when they are presented, and the temporal niche of the organism. Masking is capable of complementing entrainment, the process by which an organism is synchronized to environmental cues, if the cues are presented at an expected or predictable time-of-day, but masking can also disrupt entrainment if the cues are presented at an inappropriate time-of-day. Therefore, masking is independent of but complementary to the biological circadian pacemaker that resides within the brain (i.e., suprachiasmatic nucleus) when exogenous stimuli are presented at predictable times of day. Importantly, environmental cues are capable of either inducing sleep or wakefulness depending on the organism’s temporal niche; therefore, the same presentation of a stimulus can affect behavior quite differently in diurnal vs. nocturnal organisms. There is a growing literature examining the neural mechanisms underlying masking behavior based on the temporal niche of the organism. However, the importance of these mechanisms in governing the daily behaviors of mammals and the possible implications on human health have been gravely overlooked even as modern society enables the manipulation of these environmental cues. Recent publications have demonstrated that the effects of masking weakens significantly with old age resulting in deleterious effects on many behaviors, including sleep and wakefulness. This review will clearly outline the history, definition, and importance of masking, the environmental cues that induce the behavior, the neural mechanisms that drive them, and the possible implications for human health and medicine. New insights about how masking is affected by intrinsically photosensitive retinal ganglion cells, temporal niche, and age will be discussed as each relates to human health. The overarching goals of this review include highlighting the importance of masking in the expression of daily rhythms, elucidating the impact of aging, discussing the relationship between dysfunctional masking behavior and the development of sleep-related disorders, and considering the use of masking as a non-invasive treatment to help treat humans suffering from sleep-related disorders.

Melatonin ameliorates cognitive deficits through improving mitophagy in a mouse model of Alzheimer's disease

While melatonin is known to have protective effects in mitochondria-related diseases, aging, and neurodegenerative disorders, there is poor understanding of the effects of melatonin treatment on mitophagy in Alzheimer's disease (AD). We used proteomic analysis to investigate the effects and underlying molecular mechanisms of oral melatonin treatment on mitophagy in the hippocampus of 4-month-old wild-type mice versus age-matched 5 × FAD mice, an animal model of AD. 5 × FAD mice showed disordered mitophagy and mitochondrial dysfunction as revealed by increased mtDNA, mitochondrial marker proteins and MDA production, decreased electron transport chain proteins and ATP levels, and co-localization of Lamp1 and Tomm20. Melatonin treatment reversed the abnormal expression of proteins in the signaling pathway of lysosomes, pathologic phagocytosis of microglia, and mitochondrial energy metabolism. Moreover, melatonin restored mitophagy by improving mitophagosome-lysosome fusion via Mcoln1, and thus, ameliorated mitochondrial functions, attenuated Aβ pathology, and improved cognition. Concurrent treatment with chloroquine and melatonin blocked the positive behavioral and biochemical effects of administration with melatonin alone. Taken in concert, these results suggest that melatonin reduces AD-related deficits in mitophagy such that the drug should be considered as a therapeutic candidate for the treatment of AD.

Melatonin decreases cocaine-induced locomotor sensitization and cocaine-conditioned place preference in rats

Melatonin is a hormone that produces behavioral, pharmacological, and physiological effects through the activation of MT1 and MT2 melatonin receptors. Melatonin receptors participate in the modulation of the reinforcing effects of cocaine. Some studies report that dosing of melatonin decreases cocaine-induced locomotor activity and cocaine self-administration and that luzindole, an MT1, and MT2 melatonin receptor antagonist, blocks the melatonin-dependent decrease in cocaine-induced locomotor activity. The objective of this study was to evaluate the effect of acute or chronic dosing of melatonin on the induction and expression of cocaine-induced locomotor sensitization and cocaine-CPP in rats. Male Wistar rats received cocaine during the induction and expression of locomotor sensitization. Melatonin was administered 30 min before cocaine. After each treatment, locomotor activity was recorded for 30 min. Additionally, dopamine levels were determined in the ventral striatum, the prefrontal cortex (PFc), and the ventral tegmental area (VTA) by HPLC in animals treated with melatonin and cocaine. Melatonin decreased cocaine-induced locomotor sensitization and intracellular dopamine levels, as well as cocaine-CPP. Luzindole blocked the melatonin-induced decrease in the expression of locomotor sensitization in rats. These data suggest that melatonin may be a useful therapeutic agent to reduce cocaine abuse; additionally, they suggest that MT1 and MT2 receptors could be therapeutic targets, useful for the treatment of drug abuse disorder.