Melatonin alleviates depression-like behaviors and cognitive dysfunction in mice by regulating the circadian rhythm of AQP4 polarization

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Influencing factors of glymphatic system during perioperative period

The glymphatic system is a functional cerebrospinal fluid circulatory system that uses peri-arterial space for inflow of cerebrospinal fluid and peri-venous space for efflux of cerebrospinal fluid from brain parenchyma. This brain-wide fluid transport pathway facilitates the exchange between cerebrospinal fluid and interstitial fluid and clears metabolic waste from the metabolically active brain. Multiple lines of work show that the glymphatic system is crucial to normal brain functions, and the dysfunction of the glymphatic system is closely associated with various neurological disorders, including aging, neurodegeneration, and acute brain injury. Currently, it is common to explore the functional and molecular mechanisms of the glymphatic system based on animal models. The function of glymphatic system during perioperative period is affected by many factors such as physiological, pathological, anesthetic and operative methods. To provide a reference for the interpretation of the results of glymphatic system studies during perioperative period, this article comprehensively reviews the physiological and pathological factors that interfere with the function of the glymphatic system during perioperative period, investigates the effects of anesthetic drugs on glymphatic system function and the potential underlying mechanisms, describes operative methods that interfere with the function of the glymphatic system, and potential intervention strategies based on the glymphatic system. Future, these variables should be taken into account as critical covariates in the design of functional studies on the glymphatic system.

Daytime Dysfunction: Symptoms Associated with Nervous System Disorders Mediated by SIRT1

Daytime dysfunction, including symptoms like sleepiness, poor memory, and reduced responsiveness, is not well researched. It is crucial to develop animal models and study the biological mechanisms involved. We simulated sleep disorders through sleep deprivation, and stressful stimuli were used to establish daytime functional animal models. We used tests like the sodium pentobarbital sleep synergy test and the DSI telemetry system to measure sleep duration and structure. We also used tests like the Morris water maze, open field test, grip test, and baton twirling test to assess mental and physical fatigue. To assess the intrinsic biological mechanisms, we measured sleep-wake-related neurotransmitters and related receptor proteins, circadian rhythm-related proteins and cognition-related proteins in hypothalamus tissue, and oxidative stress, inflammatory factors, S100β, and HPA axis-related indexes in serum. Multi-factor sleep deprivation resulted in the disruption of sleep-wakefulness structure, memory-cognitive function degradation, decreased grip coordination, and other manifestations of decreased energetic and physical strength. The intrinsic biological mechanisms were related to the disturbed expression of sleep-wake, circadian rhythm, memory-cognition-related proteins, as well as the significant elevation of inflammatory factors, oxidative stress, the HPA axis, and other related indicators. Intrinsically related biological mechanisms and reduced sirt1 expression can lead to disruption of circadian rhythms; resulting in disruption of their sleep-wake-related neurotransmitter content and receptor expression. Meanwhile, the reduced expression of sirt1 also resulted in reduced expression of synapse-associated proteins. This study prepared an animal model of daytime dysfunction by means of multi-factor sleep deprivation. With sirt1 as a core target, the relevant biological mechanisms of neurological disorders were modulated.

Microglia synchronizes with the circadian rhythm of the glymphatic system and modulates glymphatic system function

Microglia, as immune cells in the central nervous system, possess the ability to adapt morphologically and functionally to their environment. Glymphatic system, the principal waste clearance system in the brain, exhibits circadian rhythms. However, the impact of microglia on the glymphatic system function remains unknown. In this study, we explored the intricate relationship between microglia and the glymphatic system. Examining diurnal patterns, we identified synchronized behaviors in glymphatic activity and microglial morphology, peaking during sleep and exhibiting distinct changes in branching complexity. Depleting microglia using PLX5622 or in P2Y12 knockout mice enhanced glymphatic function. Chemogenetic manipulation of microglia demonstrated that activating HM3D improved glymphatic function, while inhibiting HM4D unexpectedly increased microglial complexity. These findings highlight the dynamic influence of microglia on the glymphatic system.

Participation of Ca2+-Calmodulin-Dependent Protein Kinase II in the Antidepressant-Like Effects of Melatonin

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine secreted by the pineal gland during the dark phase of the photoperiod. Its main function is the synchronization of different body rhythms with the dark-light cycle. Research on melatonin has significantly advanced since its discovery and we now know that it has considerable significance in various physiological processes, including immunity, aging, and reproduction. Moreover, in recent years evidence of the pharmacological possibilities of melatonin has increased. Indoleamine, on the other hand, has antidepressant-like effects in rodents, which may be mediated by the activation of calcium-calmodulin-dependent kinase II (CaMKII) and are also related to the regulation of neuroplasticity processes, including neurogenesis, synaptic maintenance, and long-term potentiation. Remarkably, patients with major depression show decreased levels of circulating melatonin in plasma. This review presents evidence of the antidepressant-like effects of melatonin in preclinical models and the participation of CaMKII in these actions. CaMKII's role in cognition and memory processes, which are altered in depressive states, are part of the review, and the effects of melatonin in these processes are also reviewed. Furthermore, participation of CaMKII on structural and synaptic plasticity and the effects of melatonin are also described. Finally, the advantages of using melatonin in combination with other antidepressants such as ketamine for neuroplasticity are described. Evidence supports that CaMKII is activated by melatonin and downstream melatonin receptors and may be the common effector in the synergistic effects of melatonin with other antidepressants. SIGNIFICANCE STATEMENT: This review compiled evidence supporting that melatonin causes antidepressant-like effects in mice through calmodulin kinase II stimulation of downstream melatonin receptors as well as the participation of this enzyme in neuroplasticity, memory, and cognition. Finally, we describe evidence about the effectiveness of antidepressant-like effects of melatonin in combination with ketamine.

Melatonin: A potential nighttime guardian against Alzheimer's

In the context of the escalating global health challenge posed by Alzheimer's disease (AD), this comprehensive review considers the potential of melatonin in both preventive and therapeutic capacities. As a naturally occurring hormone and robust antioxidant, accumulating evidence suggests melatonin is a compelling candidate to consider in the context of AD-related pathologies. The review considers several mechanisms, including potential effects on amyloid-beta and pathologic tau burden, antioxidant defense, immune modulation, and regulation of circadian rhythms. Despite its promise, several gaps need to be addressed prior to clinical translation. These include conducting additional randomized clinical trials in patients with or at risk for AD dementia, determining optimal dosage and timing, and further determining potential side effects, particularly of long-term use. This review consolidates existing knowledge, identifies gaps, and suggests directions for future research to better understand the potential of melatonin for neuroprotection and disease mitigation within the landscape of AD.

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

Stress-induced dysfunction of neurovascular astrocytes contributes to sex-specific behavioral deficits

Astrocytes form an integral component of the neurovascular unit, ensheathing brain blood vessels with projections high in aquaporin-4 (AQP4) expression. These AQP4-rich projections facilitate interaction between the vascular endothelium, astrocytes, and neurons, and help stabilize vascular morphology. Studies using preclinical models of psychological stress and post-mortem tissue from patients with major depressive disorder (MDD) have reported reductions in AQP4, loss of astrocytic structures, and vascular impairment in the prefrontal cortex (PFC). Though compelling, the role of AQP4 in mediating stress-induced alterations in blood vessel function and behavior remains unclear. Here, we address this, alongside potential sex differences in chronic unpredictable stress (CUS) effects on astrocyte phenotype, blood-brain barrier integrity, and behavior. CUS led to pronounced shifts in stress-coping behavior and working memory deficits in male -but not female- mice. Following behavioral testing, astrocytes from the frontal cortex were isolated for gene expression analyses. We found that CUS increased various transcripts associated with blood vessel maintenance in astrocytes from males, but either had no effect on- or decreased- these genes in females. Furthermore, CUS caused a reduction in vascular-localized AQP4 and elevated extravasation of a small molecule fluorescent reporter (Dextran) in the PFC in males but not females. Studies showed that knockdown of AQP4 in the PFC in males is sufficient to disrupt astrocyte phenotype and increase behavioral susceptibility to a sub-chronic stressor. Collectively, these findings provide initial evidence that sex-specific alterations in astrocyte phenotype and neurovascular integrity in the PFC contribute to behavioral and cognitive consequences following chronic stress.

Aquaporin-4 and Parkinson's Disease

The water-selective channel aquaporin-4 (AQP4) is implicated in water homeostasis and the functioning of the glymphatic system, which eliminates various metabolites from the brain tissue, including amyloidogenic proteins. Misfolding of the α-synuclein protein and its post-translational modifications play a crucial role in the development of Parkinson's disease (PD) and other synucleopathies, leading to the formation of cytotoxic oligomers and aggregates that cause neurodegeneration. Human and animal studies have shown an interconnection between AQP4 dysfunction and α-synuclein accumulation; however, the specific role of AQP4 in these mechanisms remains unclear. This review summarizes the current knowledge on the role of AQP4 dysfunction in the progression of α-synuclein pathology, considering the possible effects of AQP4 dysregulation on brain molecular mechanisms that can impact α-synuclein modification, accumulation and aggregation. It also highlights future directions that can help study the role of AQP4 in the functioning of the protective mechanisms of the brain during the development of PD and other neurodegenerative diseases.

Correlation of Circadian Rhythms and Improvement of Depressive Symptoms in Acute Ischemic Stroke Patients

OBJECTIVES

To investigate the correlation between evening melatonin timing secretion, dim light melatonin onset (DLMO), and post-stroke depression (PSD) in acute ischemic stroke patients and their influence on the improvement of depressive symptoms.

MATERIALS AND METHODS

120 patients with a recent magnetic resonance imaging confirmed stroke were included. Salivary melatonin samples were collected at 5 time points within 1 week after hospitalization (7 p.m.-11 p.m., 1 sample per hour). The circadian phase was defined by calculating DLMO secretion. Post-stroke depressive symptoms were evaluated by the 17-item Hamilton Rating Scale for Depression (HRSD) both on day 7 of hospitalization and 3 months after stroke. Patients were divided into PSD and non-PSD groups based on whether the acute phase HRSD score was ≥8. Similarly, patients were divided into the improved depressive symptoms (IDS) and no improvement in depressive symptoms (non-IDS) groups based on whether the HRSD score at 3 months was lower than at baseline. Neurological recovery at 3 months was assessed using the modified Rankin Scale (mRS).

RESULTS

The difference in DLMO between PSD and non-PSD patients was not statistically significant (p =0.173). In the non-IDS group, there was a significant decrease in melatonin secretion at 10 p.m. (p =0.012), and DLMO was significantly later than in the IDS group (p =0.017). Logistic regression analysis showed that DLMO (OR 1.91, 95%CI:1.13-3.23, p = 0.016) was an independent risk factor for persistent no improvement in depressive symptoms, which was associated with a markedly worse prognosis (p <.001).

CONCLUSION

Our findings suggest possible interventions for the very early identification of non-IDS patients.

Altered Clock Gene Expression in Female APP/PS1 Mice and Aquaporin-Dependent Amyloid Accumulation in the Retina

Alzheimer's disease (AD), the most prevalent form of dementia, is a neurodegenerative disorder characterized by different pathological symptomatology, including disrupted circadian rhythm. The regulation of circadian rhythm depends on the light information that is projected from the retina to the suprachiasmatic nucleus in the hypothalamus. Studies of AD patients and AD transgenic mice have revealed AD retinal pathology, including amyloid-β (Aβ) accumulation that can directly interfere with the regulation of the circadian cycle. Although the cause of AD pathology is poorly understood, one of the main risk factors for AD is female gender. Here, we found that female APP/PS1 mice at 6- and 12-months old display severe circadian rhythm disturbances and retinal pathological hallmarks, including Aβ deposits in retinal layers. Since brain Aβ transport is facilitated by aquaporin (AQP)4, the expression of AQPs were also explored in APP/PS1 retina to investigate a potential correlation between retinal Aβ deposits and AQPs expression. Important reductions in AQP1, AQP4, and AQP5 were detected in the retinal tissue of these transgenic mice, mainly at 6-months of age. Taken together, our findings suggest that abnormal transport of Aβ, mediated by impaired AQPs expression, contributes to the retinal degeneration in the early stages of AD.