Response to Melatonin Treatment in Children With Autism spectrum Disorder and Relationship to Sleep Parameters and Melatonin Levels

Melatonin is one of the most used pharmacologic treatments for sleep problems in autism spectrum disorder, though its relationship with circadian and sleep parameters is still not well stablished. A naturalistic study was conducted in children with autism spectrum disorder, previously drug-naïve, before and after treatment with immediate-release melatonin. Circadian rhythms and sleep parameters were studied using an ambulatory circadian-monitoring device, and saliva samples were collected enabling determination of dim light melatonin onset. Twenty-six children with autism spectrum disorder (age 10.50  ±  2.91) were included. Immediate-release melatonin modified circadian rhythm as indicated by wrist skin temperature, showing an increase at night. A positive correlation was found between time of peak melatonin and sleep efficiency improvement values. Sleep-onset latency and efficiency improved with immediate-release melatonin. Immediate-release melatonin could be an effective treatment to improve sleep onset and restore a typical pattern of wrist temperature, which appears to be lost in autism spectrum disorder.

Assessing the pyrogenicity of whole influenza virus particle vaccine in cynomolgus macaques

Among inactivated influenza vaccines, the whole virus particle vaccine (WPV) elicits superior priming responses to split virus vaccine (SV) in efficiently inducing humoral and cellular immunity. However, there is concern for undesired adverse events such as fever for WPV due to its potent immunogenicity. Therefore, this study investigated the febrile response induced by subcutaneous injection with quadrivalent inactivated influenza vaccines of good manufacturing grade for pharmaceutical or investigational products in cynomolgus macaques. Body temperature was increased by 1 °C-2 °C for 6-12 h after WPV administration at the first vaccination but not at the second shot, whereas SV did not affect body temperature at both points. Given the potent priming ability of WPV, WPV-induced fever may be attributed to immune responses that uniquely occur during priming. Since WPV-induced fever was blunted by pretreatment with indomethacin (a cyclooxygenase inhibitor), the febrile response by WPV is considered to depend on the increase in prostaglandins synthesized by cyclooxygenase. In addition, WPV, but not SV, induced the elevation of type I interferons and monocyte chemotactic protein 1 in the plasma; these factors may be responsible for pyrogenicity caused by WPV, as they can increase prostaglandins in the brain. Notably, sufficient antibody responses were acquired by half the amount of WPV without causing fever, suggesting that excessive immune responses to trigger the febrile response is not required for acquired immunity induction. Thus, we propose that WPV with a reduced antigen dose should be evaluated for potential clinical usage, especially in naïve populations.

Role of Melatonin Receptors in Hyperthermia-Induced Acute Seizure Model of Rats

Melatonin is a neurohormone that has anticonvulsant activity in different experimental seizure models including hyperthermic febrile seizure. However, the mechanisms of this effect are not clear at the receptor level. The aim of the study was to determine which melatonin receptors involve in the hyperthermic febrile seizure model. 22-30 days Wistar male rats were used, and in children, it corresponds to 1.5-2 years. Groups were performed as (1) control, (2) ethanol/saline, (3) DMSO, (4) melatonin (MT), (5) MT + luzindole (LUZ), (6) MT + K-185, (7) MT + prazosin (PRZ), (8) MT + LUZ + K-185, (9) MT + LUZ + PRZ, (10) MT + K-185 + PRZ, and (11) MT + LUZ + PRZ + K-185. The hyperthermic febrile seizure pattern was established by keeping the rats in 45 °C hot water, and the latency, duration, and severity of seizures were determined in all groups. MT, LUZ, K-185, and PRZ were given 15, 45, 15, and 30 min before the induction of seizure, respectively. It was observed that melatonin shortened the duration of seizure, reduced the severity, and did not affect latency and that these effects were not completely blocked by receptor antagonists when compared with control, ethanol/saline, and DMSO groups. In conclusion, the fact that the anticonvulsant effect of melatonin is not completely blocked by all melatonin receptor antagonists. We can conclude that a multimodal mechanism may be responsible for the effect of melatonin receptors alone on the anticonvulsant effect of melatonin. It will be useful to design new pharmacological studies to make the subject clear.

The contribution of the pineal gland on daily rhythms and masking in diurnal grass rats, Arvicanthis niloticus

Melatonin is a hormone rhythmically secreted at night by the pineal gland in vertebrates. In diurnal mammals, melatonin is present during the inactive phase of the rest/activity cycle, and in primates it directly facilitates sleep and decreases body temperature. However, the role of the pineal gland for the promotion of sleep at night has not yet been studied in non-primate diurnal mammalian species. Here, the authors directly examined the hypothesis that the pineal gland contributes to diurnality in Nile grass rats by decreasing activity and increasing sleep at night, and that this could occur via effects on circadian mechanisms or masking, or both. Removing the pineal gland had no effect on the hourly distribution of activity across a 12:12 light-dark (LD) cycle or on the patterns of sleep-like behavior at night. Masking effects of light at night on activity were also not significantly different in pinealectomized and control grass rats, as 1h pulses of light stimulated increases in activity of sham and pinealectomized animals to a similar extent. In addition, the circadian regulation of activity was unaffected by the surgical condition of the animals. Our results suggest that the pineal gland does not contribute to diurnality in the grass rat, thus highlighting the complexity of temporal niche transitions. The current data raise interesting questions about how and why genetic and neural mechanisms linking melatonin to sleep regulatory systems might vary among mammals that reached a diurnal niche via parallel and independent pathways.

Intracoronary melatonin increases coronary blood flow and cardiac function through β-adrenoreceptors, MT1/MT2 receptors, and nitric oxide in anesthetized pigs

Melatonin is involved in the regulation of the cardiovascular system through the modulation of sympathetic function and the nitric oxide (NO)-related pathway and interaction with MT1/MT2 receptors. However, information regarding its direct actions on coronary blood flow and cardiac function is scarce. This study therefore determined the primary in vivo effect of melatonin on cardiac function and perfusion and the involvement of the autonomic nervous system, MT1/MT2 receptors, and NO. In 35 pigs, melatonin infused into the coronary artery at 70 pg for each mL/min of coronary blood flow while preventing changes in heart rate and arterial pressure increased coronary blood flow, dP/dt(max), segmental shortening, and cardiac output by about 12%, 14%, 8%, and 23% of control values (P < 0.05), respectively. These effects were accompanied by an increase in coronary NO release of about 46% (P < 0.05) of control values. The aforementioned responses were graded in a further five pigs. Moreover, the blockade of muscarinic cholinoreceptors (n = 5) and α-adrenoreceptors (n = 5) did not abolish the observed responses to melatonin. After β(1)-adrenoreceptors blocking (n = 5), melatonin failed to affect cardiac function, whereas β(2)-adrenoreceptors (n = 5) and NO synthase inhibition (n = 5) prevented the coronary response and the effect of melatonin on NO release. Finally, all effects were prevented by MT1/MT2 receptor inhibitors (n = 10). In conclusion, melatonin primarily increased coronary blood flow and cardiac function through the involvement of MT1/MT2 receptors, β-adrenoreceptors, and NO release. These findings add new information about the mechanisms through which melatonin physiologically modulates cardiovascular function and exerts cardioprotective effects.

Update on the use of melatonin in pediatrics

Melatonin, an endogenously produced indoleamine, is a highly effective antioxidant, free radical scavenger, and a primary circadian regulator. Melatonin has important antioxidant properties owing to direct and indirect effects. It directly scavenges reactive oxygen and reactive nitrogen species, prevents molecular oxidation, improves mitochondrial physiology, and restores glutathione homeostasis. Its indirect antioxidant effects stem from its ability to stimulate the activities of the enzymes involved in the glutathione cycling and production. Melatonin, by reducing free radical damage, may be an effective protective agent for the fetus as it is in adults. Several clinical studies on melatonin have shown that it reduces oxidative stress in human newborns with sepsis, hypoxic distress, or other conditions, where there is excessive free radical generation. A role of melatonin in infant development has also been suggested. Pineal dysfunction may be associated with deleterious outcomes in infants and may contribute to an increased prevalence of sudden infant death syndrome. Delayed melatonin production is evident in infants who had experienced an apparent life-threatening event. Melatonin has been used as a pharmacologic treatment for insomnias associated with shift work, jet lag, and delayed sleep onset in adults for decades. In children as well, melatonin has value as a sleep-promoting agent. Evidence suggests that melatonin has utility as an analgesic agent presumably related to its ability to release β-endorphin. The data support the notion that melatonin, or one of its analogs, might find use as an anesthetic agent in children.