Long-term morphological and functional evaluation of the neuroprotective effects of post-ischemic treatment with melatonin in rats

Melatonin as an Antioxidant Agent in Stroke: An Updated Review

Stroke is a devastating disease associated with high mortality and disability worldwide, and is generally classified as ischemic or hemorrhagic, which share certain similar pathophysiological processes. Oxidative stress is a critical factor involved in stroke-induced injury, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, brain edema, and neuronal death. To alleviate these serious secondary brain injuries, neuroprotective agents targeting oxidative stress inhibition may serve as a promising treatment strategy. Melatonin is a hormone secreted by the pineal gland, and has various properties, such as antioxidation, anti-inflammation, circadian rhythm modulation, and promotion of tissue regeneration. Numerous animal experiments studying stroke have confirmed that melatonin exerts considerable neuroprotective effects, partially via anti-oxidative stress. In this review, we introduce the possible role of melatonin as an antioxidant in the treatment of stroke based on the latest published studies of animal experiments and clinical research.

Prophylactic Melatonin Treatment Ameliorated Propofol-Induced Cognitive Dysfunction in Aged Rats

Considering the fact that melatonin acts as protective agent in various cognitive impairment, we decided to explore the precise effect of pretreatment with melatonin on cognitive function, mitochondrial activity, apoptosis and synaptic integrity in aged rats anesthetized by propofol. We first randomly allocated the thirty Sprague Dawley rats into three groups: Control vehicle-treated group (Con), Propofol-treated group (Pro) and Melatonin + Propofol group (Mel + Pro). The Barnes maze, open field and contextual fear conditioning test were employed to evaluate spatial memory, exploratory behavior and general locomotor activity, and hippocampus-dependent learning and memory ability, respectively. Moreover, mitochondrial function (including reactive oxygen species, mitochondrial membrane potential and ATP levels) and apoptosis were detected in the regions of hippocampus (HIP) and prefrontal cortex (PFC). The results of behavioral tests suggested that melatonin improved propofol-induced memory impairment in aged rats. Melatonin mitigated mitochondrial dysfunction and decreased the apoptotic cell counts in the regions of HIP and PFC. Furthermore, prophylactic melatonin treatment also reversed the propofol-induced inactivation of PKA/CREB/BDNF signaling and synaptic dysfunction. On the whole, our results indicated that melatonin ameliorated the propofol-induced cognitive disorders via attenuating mitochondrial dysfunction, apoptosis, inactivation of PKA/CREB/BDNF signaling and synaptic dysfunction.

Melatonin regulates neuroinflammation ischemic stroke damage through interactions with microglia in reperfusion phase

Even today, ischemic stroke is a major cause of death and disabilities because of its high incidence, limited treatments and poor understanding of the pathophysiology of ischemia/reperfusion, neuroinflammation and secondary injuries following ischemic stroke. The function of microglia as a part of the immune system of the brain following ischemic stroke can be destructive or protective. Recent surveys indicate that melatonin, a strong antioxidant agent, has receptors on microglial cells and can regulate them to protective form; yet, more findings are required for better understanding of this mechanism, particularly in the reperfusion phase. In this study, we initially aimed to evaluate the therapeutic efficacy of melatonin intra-arterially and to clarify the underlying mechanisms. After that by using an in vitro approach, we evaluated the protective effects of melatonin on microglial cells following the hypoxia condition. Our results proved that a single dose of melatonin at the beginning of reperfusion phase improved structural and behavioral outcomes. Melatonin increased NeuN and decreased GFAP, Iba1 and active caspase-3 at protein level. Furthermore, melatonin elevated BDNF, MAP2, HSPA1A and reduced VEGF at mRNA level. We also showed that melatonin receptor 1B highly expressed in microglial cells after 3 h hypoxia. Besides, melatonin increased the ratio of TREM2/iNOS as a marker of the most protective form of microglia (M2). In summary, our data suggest that melatonin has the possibility to serve as targeting microglial action for preventing secondary injury of reperfusion phase after ischemic stroke.

Role of Melatonin in Aluminum-Related Neurodegenerative Disorders: a Review

Aluminum (Al), a potentially neurotoxic element, provokes various adverse effects on human health such as dialysis dementia, osteomalacia, and microcytic anemia. It has been also associated with serious neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis, and Parkinsonism dementia of Guam. The "aluminum hypothesis" of AD assumes that the metal complexes can potentiate the rate of aggregation of amyloid-β (Aβ), enhancing the toxicity of this peptide, and being able of contributing to the pathogenesis of AD. It has been supported by a number of analytical, epidemiological, and neurotoxicological studies. On the other hand, melatonin (Mel) is a potent direct free radical scavenger and indirect antioxidant, which acts increasing the activity of important related antioxidant enzymes, and preventing oxidative stress and cell death of neurons exposed to Aβ-induced neurotoxicity. Therefore, Mel might be useful in the treatment of AD by reducing the Aβ generation and by inhibiting mitochondrial cell death pathways. The present review on the role of Mel in Al-related neurodegenerative disorders concludes that the protective effects of this hormone, together with its low toxicity, support the administration of Mel as a potential supplement in the treatment of neurological disorders, in which oxidative stress is involved.

Cerebrovascular Disease in the Young Adult: Examining Melatonin's Possible Multiple Roles

In the last decade or more, there have been reports suggesting a rise in the incidence of stroke in young adults. Presently, it appears that the risk factors associated with the cause of stroke in young adults remain relatively constant across different geographic regions of the world. Moreover, the endogenous rhythm of a neurohormone such as melatonin is known to play certain roles in the modulation of some of the risk factors that are associated with an increased risk of stroke in young people. Whereas animal studies have shown that melatonin plays diverse roles in stroke, only a limited number of human studies examined the roles of exogenous melatonin administration in the prevention of stroke, attenuation of neuronal damage, and improving outcome or well-being in stroke patients. In this review, first we summarize existing studies of stroke in the young adult and then provide insights on melatonin and stroke. Thereafter, we discuss the role of melatonin in models of stroke and how melatonin can be regulated to prevent stroke in young adults. Finally, we highlight the possible roles of melatonin in the management and outcome of stroke, especially in the young adult stroke population.

Melatonin improves vascular cognitive impairment induced by ischemic stroke by remyelination via activation of ERK1/2 signaling and restoration of glutamatergic synapses in the gerbil hippocampus

Vascular dementia affects cognition by damaging axons and myelin. Melatonin is pharmacologically associated with various neurological disorders. In this study, effects of melatonin on cognitive impairment and related mechanisms were investigated in an animal model of ischemic vascular dementia (IVD). Melatonin was intraperitoneally administered to adult gerbils after transient global cerebral ischemia (tGCI) for 25 days beginning 5 days after tGCI. Cognitive impairment was examined using a passive avoidance test and the Barnes maze test. To investigate mechanisms of restorative effects by melatonin, neuronal damage/death, myelin basic protein (MBP, a marker for myelin), Rip (a marker for oligodendrocyte), extracellular signal-regulated protein kinase1/2 (ERK1/2) and phospho-ERK1/2 (p-ERK1/2), and vesicular glutamate transporter (VGLUT)-1 (a glutamatergic synaptic marker) in the hippocampal Cornu Ammonis 1 area (CA1) were evaluated using immunohistochemistry. Melatonin treatment significantly improved tGCI-induced cognitive impairment. Death of CA1 pyramidal neurons after tGCI was not affected by melatonin treatment. However, melatonin treatment significantly increased MBP immunoreactivity and numbers of Rip-immunoreactive oligodendrocytes in the ischemic CA1. In addition, melatonin treatment significantly increased ERK1/2 and p-ERK1/2 immunoreactivities in oligodendrocytes in the ischemic CA1. Furthermore, melatonin treatment significantly increased VGLUT-1 immunoreactive structures in the ischemic CA1. These results indicate that long-term melatonin treatment after tGCI improves cognitive deficit via restoration of myelin, increase of oligodendrocytes which is closely related to the activation of ERK1/2 signaling, and increase of glutamatergic synapses in the ischemic brain area.

Acupuncture Rescues Cognitive Impairment and Upregulates Dopamine-β-Hydroxylase Expression in Chronic Cerebral Hypoperfusion Rats

Alteration of dopamine (DA) and noradrenaline (NA) contributes to cognitive function. Acupuncture has been shown to affect DA and NA in chronic cerebral hypoperfusion (CCH) rats. However, the effect of acupuncture on DA-β-hydroxylase (DBH), the biosynthetic enzyme of NA, remains unknown. In CCH rats we established chronic hypoperfusion by bilateral common carotid artery occlusion (two-vessel occlusion, 2VO) and treated them with acupuncture. Acupuncture displayed beneficial effects on hippocampus-dependent memory impairments, including nonspatial and spatial memory. That is also reflected in hippocampus long-term-potentiation (LTP). Moreover, DBH expression in the hippocampus and DBH activity in cerebrospinal fluid were upregulated after acupuncture treatment. In conclusion, these in vivo findings suggest that acupuncture exerts a therapeutic effect on hippocampus-dependent memory and hippocampus LTP in CCH rats, which may be partially related to the modulation of DBH in the hippocampus.

Melatonin ameliorates cognitive memory by regulation of cAMP-response element-binding protein expression and the anti-inflammatory response in a rat model of post-traumatic stress disorder

BACKGROUND

Post-traumatic stress disorder (PTSD) is an important psychological disease that can develop following the physical experience or witnessing of traumatic events. The psychopathological response to traumatic stressors increases inflammation in the hippocampus and induces memory deficits. Melatonin (MTG) plays critical roles in circadian rhythm disorders, Alzheimer's disease, and other neurological disorders. However, the cognitive efficiency of MTG and its mechanisms of action in the treatment of PTSD remain unclear. Thus, the present study investigated the effects of MTG on spatial cognitive impairments stimulated by single prolonged stress (SPS) in rats, an animal model of PTSD. Male rats received intraperitoneal (i.p.) administration of various doses of MTG for 21 consecutive days after the SPS procedure.

RESULTS

SPS-stimulated cognitive impairments in the object recognition task and Morris water maze were reversed by MTG treatment (25 mg/kg, i.p). Additionally, MTG significantly increased cognitive memory-related decreases in cAMP-response element-binding (CREB) protein and mRNA levels in the hippocampus. Our results also demonstrate that MTG significantly inhibited SPS-stimulated cognitive memory impairments by inhibiting the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in the rat brain.

CONCLUSION

The present results indicate that MTG can be beneficial for SPS-stimulated memory impairments via changes in CREB expression and proinflammatory mediators. Thus, MTG may be a prophylactic strategy for the prevention or mitigation of the progression of some features of the PTSD pathology.

Understanding the role of steroids in typical and atypical brain development: Advantages of using a "brain in a dish" approach

Steroids have an important role in growth, development, sexual differentiation and reproduction. All four classes of steroids, androgens, oestrogens, progestogens and glucocorticoids, have varying effects on the brain. Androgens and oestrogens are involved in the sexual differentiation of the brain, and also influence cognition. Progestogens such as progesterone and its metabolites have been shown to be involved in neuroprotection, although their protective effects are timing-dependent. Glucocorticoids are linked with stress and memory performance, also in a dose- and time-dependent manner. Importantly, dysfunction in steroid function has been implicated in the pathogenesis of disease. Moreover, regulating steroid-signalling has been suggested as potential therapeutic avenue for the treatment of a number of neurodevelopmental, psychiatric and neurodegenerative disorders. Therefore, clarifying the role of steroids in typical and atypical brain function is essential for understanding typical brain functions, as well as determining their potential use for pharmacological intervention in the atypical brain. However, the majority of studies have thus far have been conducted using animal models, with limited work using native human tissue or cells. Here, we review the effect of steroids in the typical and atypical brain, focusing on the cellular, molecular functions of these molecules determined from animal models, and the therapeutic potential as highlighted by human studies. We further discuss the promise of human-induced pluripotent stem cells, including advantages of using three-dimensional neuronal cultures (organoids) in high-throughput screens, in accelerating our understanding of the role of steroids in the typical brain, and also with respect to their therapeutic value in the understanding and treatment of the atypical brain.

Hippocampal Deformations and Entorhinal Cortex Atrophy as an Anatomical Signature of Long-Term Cognitive Impairment: from the MCAO Rat Model to the Stroke Patient

Stroke patients have an elevated risk of developing long-term cognitive disorders or dementia. The latter is often associated with atrophy of the medial temporal lobe. However, it is not clear whether hippocampal and entorhinal cortex atrophy is the sole predictor of long-term post-stroke dementia. We hypothesized that hippocampal deformation (rather than atrophy) is a predictive marker of long-term post-stroke dementia on a rat model and tested this hypothesis in a prospective cohort of stroke patients.Male Wistar rats were subjected to transient middle cerebral artery occlusion and assessed 6 months later. Ninety initially dementia-free patients having suffered a first-ever ischemic stroke were prospectively included in a clinical study. In the rat model, significant impairments in hippocampus-dependent memories were observed. MRI studies did not reveal significant atrophy of the hippocampus volume, but significant deformations were indeed observed-particularly on the ipsilateral side. There, the neuronal surface area was significantly lower in ischemic rats and was associated with a lower tissue density and a markedly thinner entorhinal cortex. At 6 months post-stroke, 49 of the 90 patients displayed cognitive impairment (males 55.10%). Shape analysis revealed marked deformations of their left hippocampus, a significantly lower entorhinal cortex surface area, and a wider rhinal sulcus but no hippocampal atrophy. Hence, hippocampal deformations and entorhinal cortex atrophy were associated with long-term impaired cognitive abilities in a stroke rat model and in stroke patients. When combined with existing biomarkers, these markers might constitute sensitive new tools for the early prediction of post-stroke dementia.

Upregulation of Cdh1 signaling in the hippocampus attenuates brain damage after transient global cerebral ischemia in rats

Cerebral ischemia is a major cause of brain dysfunction. The E3 ubiquitin ligase anaphase-promoting complex and its coactivator Cdh1 have been reported to be involved in the regulation of neuronal survival, differentiation, axonal growth and synaptic development in the central nervous system. However, its role in the ischemic brain and the underlying mechanisms remain poorly understood. The present study aimed to investigate the effects of Cdh1 overexpression on the ischemic rat brain by direct intra-hippocampal injection of lentivirus-delivered Cdh1 before transient global cerebral ischemia reperfusion. Spatial memory acquisition and retention were assessed using a Morris water maze task. Neuronal damage, glial activation, oxidative stress and the synaptic ultrastructure were also examined. The results indicated that a recombinant Cdh1-encoding lentiviral vector can upregulate the expression of Cdh1 in the rat hippocampus. Cdh1 overexpression increased the survival rates of rats, reversed the abnormal accumulation of cyclin B1, alleviated neuronal death, inhibited glial activation, mitigated oxidative stress, modulated synaptic plasticity and improved neurological deficits caused by ischemia. Our study indicates that targeting the Cdh1 signaling pathway in the hippocampus may provide a promising therapeutic strategy for the clinical treatment of transient global cerebral ischemia.

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

Melatonin as an antioxidant: under promises but over delivers

Melatonin is uncommonly effective in reducing oxidative stress under a remarkably large number of circumstances. It achieves this action via a variety of means: direct detoxification of reactive oxygen and reactive nitrogen species and indirectly by stimulating antioxidant enzymes while suppressing the activity of pro-oxidant enzymes. In addition to these well-described actions, melatonin also reportedly chelates transition metals, which are involved in the Fenton/Haber-Weiss reactions; in doing so, melatonin reduces the formation of the devastatingly toxic hydroxyl radical resulting in the reduction of oxidative stress. Melatonin's ubiquitous but unequal intracellular distribution, including its high concentrations in mitochondria, likely aid in its capacity to resist oxidative stress and cellular apoptosis. There is credible evidence to suggest that melatonin should be classified as a mitochondria-targeted antioxidant. Melatonin's capacity to prevent oxidative damage and the associated physiological debilitation is well documented in numerous experimental ischemia/reperfusion (hypoxia/reoxygenation) studies especially in the brain (stroke) and in the heart (heart attack). Melatonin, via its antiradical mechanisms, also reduces the toxicity of noxious prescription drugs and of methamphetamine, a drug of abuse. Experimental findings also indicate that melatonin renders treatment-resistant cancers sensitive to various therapeutic agents and may be useful, due to its multiple antioxidant actions, in especially delaying and perhaps treating a variety of age-related diseases and dehumanizing conditions. Melatonin has been effectively used to combat oxidative stress, inflammation and cellular apoptosis and to restore tissue function in a number of human trials; its efficacy supports its more extensive use in a wider variety of human studies. The uncommonly high-safety profile of melatonin also bolsters this conclusion. It is the current feeling of the authors that, in view of the widely diverse beneficial functions that have been reported for melatonin, these may be merely epiphenomena of the more fundamental, yet-to-be identified basic action(s) of this ancient molecule.

Effects of melatonin on cognitive impairment and hippocampal neuronal damage in a rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH), which induces oxidative stress and inflammation in the brain, has previously been associated with cognitive impairment and neuronal cell damage. Melatonin is a well-known free radical scavenger and antioxidant; therefore, the present study investigated the protective effects of melatonin against CCH-induced cognitive impairment and neuronal cell death in a CCH rat model, which was generated via permanent bilateral common carotid artery occlusion (2VO). The rats in the 2VO group exhibited markedly increased escape latencies in a Morris water maze test, as compared with the rats in the sham group. In addition, increased neuronal cell damage was detected in the hippocampal CA1 region of the 2VO rats, as compared with the rats in the sham group. Treatment of the 2VO rats with melatonin significantly reduced the escape latency and neuronal cell damage, and was associated with reduced levels of malondialdehyde, microglial activation, and tumor necrosis factor-α and interleukin-1β in the ischemic hippocampus. The results of the present study suggest that melatonin may attenuate CCH-induced cognitive impairment and hippocampal neuronal cell damage by decreasing oxidative stress, microglial activation and the production of pro-inflammatory cytokines in the ischemic hippocampus.

Prophylactic melatonin significantly reduces Alzheimer's neuropathology and associated cognitive deficits independent of antioxidant pathways in AβPP(swe)/PS1 mice

Background

Alzheimer’s disease (AD) underlies dementia for millions of people worldwide, and its occurrence is set to double in the next 20 years. Currently, approved drugs for treating AD only marginally ameliorate cognitive deficits, and provide limited symptomatic relief, while newer substances under therapeutic development are potentially years away from benefiting patients. Melatonin (MEL) for insomnia has been proven safe with >15 years of over-the-counter access in the US. MEL exerts multiple complementary mechanisms of action against AD in animal models; thus it may be an excellent disease-modifying therapeutic. While presumed to provide neuroprotection via activation of known G-protein-coupled melatonin receptors (MTNRs), some data indicate MEL acts intracellularly to protect mitochondria and neurons by scavenging reactive oxygen species and reducing free radical formation. We examined whether genetic deletion of MTNRs abolishes MEL’s neuroprotective actions in the AβPP^swe/PSEN1dE9 mouse model of AD (2xAD). Beginning at 4 months of age, both AD and control mice either with or without both MTNRs were administered either MEL or vehicle in drinking water for 12 months.

Results

Behavioral and cognitive assessments of 15-month-old AD mice revealed receptor-dependent effects of MEL on spatial learning and memory (Barnes maze, Morris Water Maze), but receptor-independent neuroprotective actions of MEL on non-spatial cognitive performance (Novel Object Recognition Test). Similarly, amyloid plaque loads in hippocampus and frontal cortex, as well as plasma Aβ_1–42 levels, were significantly reduced by MEL in a receptor-independent manner, in contrast to MEL’s efficacy in reducing cortical antioxidant gene expression (Catalase, SOD1, Glutathione Peroxidase-1, Nrf2) only when receptors were present. Increased cytochrome c oxidase activity was seen in 16mo AD mice as compared to non-AD control mice. This increase was completely prevented by MEL treatment of 2xAD/MTNR+ mice, but only partially prevented in 2xAD/MTNR- mice, consistent with mixed receptor-dependent and independent effects of MEL on this measure of mitochondrial function.

Conclusions

These findings demonstrate that prophylactic MEL significantly reduces AD neuropathology and associated cognitive deficits in a manner that is independent of antioxidant pathways. Future identification of direct molecular targets for MEL action in the brain should open new vistas for development of better AD therapeutics.

Melatonin ameliorates cognitive impairment induced by sleep deprivation in rats: role of oxidative stress, BDNF and CaMKII

Sleep deprivation (SD) has been shown to induce oxidative stress which causes cognitive impairment. Melatonin, an endogenous potent antioxidant, protects neurons from oxidative stress in many disease models. The present study investigated the effect of melatonin against SD-induced cognitive impairment and attempted to define the possible mechanisms involved. SD was induced in rats using modified multiple platform model. Melatonin (15 mg/kg) was administered to the rats via intraperitoneal injection. The open field test and Morris water maze were used to evaluate cognitive ability. The cerebral cortex (CC) and hippocampus were dissected and homogenized. Nitric oxide (NO) and malondialdehyde (MDA) levels and the superoxide dismutase (SOD) enzyme activity of hippocampal and cortical tissues (10% wet weight per volume) were performed to determine the level of oxidative stress. The expression of brain-derived neurotrophic factor (BDNF) and calcium-calmodulin dependent kinase II (CaMKII) proteins in CC and hippocampus was assayed by means of immunohistochemistry. The results revealed that SD impairs cognitive ability, while melatonin treatment prevented these changes. In addition, melatonin reversed SD-induced changes in NO, MDA and SOD in both of the CC and hippocampus. The results of immunoreactivity showed that SD decreased gray values of BDNF and CaMKII in CC and hippocamal CA1, CA3 and dentate gyrus regions, whereas melatonin improved the gray values. In conclusion, our results suggest that melatonin prevents cognitive impairment induced by SD. The possible mechanism may be attributed to its ability to reduce oxidative stress and increase the levels of CaMKII and BDNF in CC and hippocampus.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

Melatonin's protective action against ischemic neuronal damage is associated with up-regulation of the MT2 melatonin receptor

Melatonin is a potent free radical scavenger and antioxidant and has protective effects against ischemic damage. In the present study, we examined the relationship between the neuroprotective effects of melatonin and the activation of MT2 melatonin receptor in the hippocampal CA1 region (CA1) after transient cerebral ischemia. MT2 immunoreactivity and protein levels were increased in the CA1 after ischemic damage. Most of MT2-immunoreactive cells were colocalized with astrocytes, not microglia, in the ischemic CA1. In the melatonin-sham group, MT2 immunoreaction and protein levels were increased compared with the sham group, and MT2 immunoreactivity and its protein levels in the melatonin-ischemia group were similar to those in the melatonin-sham group. In addition, melatonin treatment attenuated the activation of astrocytes and microglia. These results indicate that MT2 are increased and expressed in astrocytes in the ischemic region after an ischemic insult. The activation of MT2 melatonin receptor in the CA1 after melatonin treatment may be involved in the neuroprotective effect associated with melatonin after ischemic injury.

Chronic treatment with melatonin stimulates dendrite maturation and complexity in adult hippocampal neurogenesis of mice

In the course of adult hippocampal neurogenesis, the postmitotic maturation and survival phase is associated with dendrite maturation. Melatonin modulates the survival of new neurons with relative specificity. During this phase, the new neurons express microtubule-associated protein doublecortin (DCX). Here, we show that the entire population of cells expressing DCX is increased after 14 days of treatment with melatonin. As melatonin also affects microtubule polymerization which is important for neuritogenesis and dendritogenesis, we studied the consequences of chronic melatonin administration on dendrite maturation of DCX-positive cells. Treatment with melatonin increased the number of DCX-positive immature neurons with more complex dendrites. Sholl analysis revealed that melatonin treatment lead to greater complexity of the dendritic tree. In addition, melatonin increased the total volume of the granular cell layer. Besides its survival-promoting effect, melatonin thus also increases dendritic maturation in adult neurogenesis. This might open the opportunity of using melatonin as an adjuvant in attempts to extrinsically stimulate adult hippocampal neurogenesis in neuropsychiatric disease, dementia or cognitive ageing.

Synergistic neuroprotective therapies with hypothermia

Neuroprotection is a major health care priority, given the enormous burden of human suffering and financial cost caused by perinatal brain damage. With the advent of hypothermia as therapy for term hypoxic-ischemic encephalopathy, there is hope for repair and protection of the brain after a profound neonatal insult. However, it is clear from the published clinical trials and animal studies that hypothermia alone will not provide complete protection or stimulate the repair that is necessary for normal neurodevelopmental outcome. This review critically discusses drugs used to treat seizures after hypoxia-ischemia in the neonate with attention to evidence of possible synergies for therapy. In addition, other agents such as xenon, N-acetylcysteine, erythropoietin, melatonin and cannabinoids are discussed as future potential therapeutic agents that might augment protection from hypothermia. Finally, compounds that might damage the developing brain or counteract the neuroprotective effects of hypothermia are discussed.

Melatonin promotes distal dendritic ramifications in layer II/III cortical pyramidal cells of rats exposed to toluene vapors

We have previously shown that toluene inhalation produces significant impairments in the basilar dendritic outgrowth of pyramidal cortical cells. This neurotoxic effect was markedly inhibited by melatonin administration at a dose of 5mg kg(-1). The present study was designed to determine whether toluene and melatonin equally affect all basilar dendritic segments or if a differential response exists between the segments. Twenty-eight male mice were weaned at postnatal day 21 (P21) and randomly assigned to either the control (C; n=10,) or toluene (T; n=18) group. Between P22-P32, male rats were placed into a glass chamber and exposed to either toluene vapors (5-000-6000 ppm) or clean air for 10 min a day. When toluene exposure ended (P32), animals were further assigned to the following experimental groups: (a) control/saline (C/S; n=10), (b) toluene/saline (T/S; n=10), or (c) toluene/melatonin 5mg kg(-1) (T/M; n=8). Melatonin or vehicle solutions were administered daily between P32 and P38. Forty-eight hours after the final toluene exposure, the animals were sacrificed, and the pyramidal cortical cells were stained using the Golgi-Cox-Sholl procedure. The number of basilar dendritic branches/order was counted using the centrifugal ordering method. The results indicate that (i) toluene inhalation significantly impairs both proximal and distal basilar dendritic ramifications (in the parietal and frontal/occipital cortices, respectively) and (ii) melatonin both protects neurons from toluene neurotoxicity in all cortical areas studied and increases the complexity of the dendritic tree above control values.

Melatonin improves presynaptic protein, SNAP-25, expression and dendritic spine density and enhances functional and electrophysiological recovery following transient focal cerebral ischemia in rats

Synapto-dendritic dysfunction and rearrangement takes place over time at the peri-infarct brain after stroke, and the event plays an important role in post-stroke functional recovery. Here, we evaluated whether melatonin would modulate the synapto-dendritic plasticity after stroke. Adult male Sprague-Dawley rats were treated with melatonin (5 mg/kg) or vehicle at reperfusion onset after transient occlusion of the right middle cerebral artery (tMCAO) for 90 min. Local cerebral blood perfusion, somatosensory electrophysiological recordings and neurobehavioral tests were serially measured. Animals were sacrificed at 7 days after tMCAO. The brain was processed for Nissl-stained histology, Golgi-Cox-impregnated sections, or Western blotting for presynaptic proteins, synaptosomal-associated protein of 25 kDa (SNAP-25) and synaptophysin (a calcium-binding protein found on presynaptic vesicle membranes). Relative to controls, melatonin-treated animals had significantly reduced infarction volumes (P < 0.05) and improved neurobehavioral outcomes, as accessed by sensorimotor and rota-rod motor performance tests (P < 0.05, respectively). Melatonin also significantly improved the SNAP-25, but not synaptophysin, protein expression in the ischemic brain (P < 0.05). Moreover, melatonin significantly improved the dendritic spine density and the somatosensory electrophysiological field potentials both in the ischemic brain and the contralateral homotopic intact brain (P < 0.05, respectively). Together, melatonin not only effectively attenuated the loss of presynaptic protein, SANP-25, and dendritic spine density in the ischemic territory, but also improved the reductions in the dendritic spine density in the contralateral intact brain. This synapto-dendritic plasticity may partly account for the melatonin-mediated improvements in functional and electrophysiological circuitry after stroke.

Effects of melatonin in experimental stroke models in acute, sub-acute, and chronic stages

Melatonin (n-acetyl-5-methoxy-tryptamine), a naturally occurring indole produced mainly by the pineal gland, is a well known antioxidant. Stroke (cerebral ischemia) is the second leading cause of death worldwide. To date, however, effective and safe treatment for stroke remains unavailable. Melatonin is both lipid- and water-soluble and readily crosses the blood-brain barrier (BBB). Increasing evidence has shown that, in animal stroke models, administering melatonin significantly reduces infarct volume, edema, and oxidative damage and improves electrophysiological and behavioral performance. Here, we reviewed studies that assess effects of melatonin on cerebral ischemia in acute, sub-acute, and chronic stages. In addition to its potent antioxidant properties, melatonin exerts antiapoptotic, antiexcitotoxic, anti-inflammatory effects and promotes mitochondrial functions in animals with cerebral ischemia. Given that melatonin shows almost no toxicity to humans and possesses multifaceted protective capacity against cerebral ischemia, it is valuable to consider using melatonin in clinical trials on patients suffering from stroke.

Cellular and biochemical actions of melatonin which protect against free radicals: role in neurodegenerative disorders

Molecular oxygen is toxic for anaerobic organisms but it is also obvious that oxygen is poisonous to aerobic organisms as well, since oxygen plays an essential role for inducing molecular damage. Molecular oxygen is a triplet radical in its ground-stage (.O-O.) and has two unpaired electrons that can undergoes consecutive reductions of one electron and generates other more reactive forms of oxygen known as free radicals and reactive oxygen species. These reactants (including superoxide radicals, hydroxyl radicals) possess variable degrees of toxicity. Nitric oxide (NO*) contains one unpaired electron and is, therefore, a radical. NO* is generated in biological tissues by specific nitric oxide synthases and acts as an important biological signal. Excessive nitric oxide production, under pathological conditions, leads to detrimental effects of this molecule on tissues, which can be attributed to its diffusion-limited reaction with superoxide to form the powerful and toxic oxidant, peroxynitrite.Reactive oxygen and nitrogen species are molecular "renegades"; these highly unstable products tend to react rapidly with adjacent molecules, donating, abstracting, or even sharing their outer orbital electron(s). This reaction not only changes the target molecule, but often passes the unpaired electron along to the target, generating a second free radical, which can then go on to react with a new target amplifying their effects.This review describes the mechanisms of oxidative damage and its relationship with the most highly studied neurodegenerative diseases and the roles of melatonin as free radical scavenger and neurocytoskeletal protector.

Melatonin treatment in peri- and postmenopausal women elevates serum high-density lipoprotein cholesterol levels without influencing total cholesterol levels

The purpose of this study was to investigate the effects of melatonin on lipid metabolism in peri- and postmenopausal women. Forty-six women were enrolled in these studies. The relationship between night-time serum melatonin levels and serum total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol was investigated in 36 women. Night-time serum melatonin levels had a negative correlation with serum total cholesterol and LDL-cholesterol, and a loose positive correlation with HDL-cholesterol. To examine the effects of exogenous melatonin on lipid metabolism, serum levels of total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides were determined in 10 women before the onset of therapy and after 1 month of oral melatonin administration (1 mg melatonin daily). Melatonin administration significantly increased the serum levels of HDL-cholesterol. These results show that melatonin may influence cholesterol metabolism and suggest that the melatonin administration may become a new medical application for improvement of lipid metabolism and prevention of cardiovascular disease in peri- and postmenopausal women.

Chronic and acute melatonin effects in gerbil global forebrain ischemia: long-term neural and behavioral outcome

Melatonin attenuates the short-term consequences of brain ischemia in several animal models. However, there is scant information regarding its efficacy for improving the long-term outcome. To further address that issue, we subjected gerbils to 5-min bilateral carotid occlusion. Some gerbils received acute peri-surgical administration of melatonin while others received continuous melatonin in their water. The gerbils' brains were histologically assessed at 20 wk postsurgery. Chronic but not acute melatonin attenuated ischemia-induced hyperactivity at 3 days postsurgery. Twenty weeks postsurgery, the ischemic gerbils showed varying degrees of bilateral loss of hippocampal CA1 pyramidal cells and elevation of glial fibrillary acidic protein immunoreactivity there. Both the cell loss and the immunoreactivity were markedly asymmetrical for some gerbils. Neither acute nor chronic melatonin altered this pattern of CA1 cell loss and glial immunoreactivity increase. Ischemia increased the number of CA1 cells that were immunoreactive for doublecortin (DCX), a marker for newborn neurons. This increase in CA1 DCX expression was not affected by either melatonin treatment. However, both acute and chronic melatonin reduced the number of DCX immunoreactive neurons in the dentate gyrus. Thus, neither acute nor chronic melatonin altered the long-term neural outcome of forebrain ischemia, although chronic administration seemed to attenuate the short-term behavioral effect. It is suggested that persistently high brain levels of melatonin may be essential for long-term neuroprotection against ischemia. The possibility that melatonin may modulate hippocampal neurogenesis merits further exploration both in normal animals and in models of brain insult.

Melatonin and the human hippocampus, a time dependent interplay

Melatonin serves as a signal of darkness and participates in sleep/wake regulation. Animal studies demonstrated effects of melatonin in the hippocampus, particularly suggesting involvement in synaptic plasticity. We used functional magnetic resonance imaging to identify and investigate effects of melatonin in the human hippocampus. Activity in the hippocampal complex during a memory task was examined at 22:00 hr (when endogenous melatonin levels are normally increasing) and compared with 16:00 hr (when endogenous melatonin levels are minimal). The relationship between observed activation patterns and endogenous melatonin was assessed. Finally, the effects of exogenous melatonin administered at 22:00 hr were studied in a double-blind, placebo-controlled crossover manner. Our findings indicate that activation in the left hippocampus at 22:00 hr is significantly reduced compared with afternoon hours compatible with diurnal variation in hippocampal activity. Exogenous melatonin further reduced activation in this region, only in subjects who already crossed the melatonin onset phase at this hour and in correlation with endogenous melatonin levels. As such an effect was not demonstrated with afternoon administration of melatonin, a time depended effect is suggested. Contrary, activation in the left para-hippocampus at 22:00 hr was higher in subjects that crossed the melatonin onset phase. Parahippocampal activation correlated with individual endogenous melatonin levels and was not further affected by exogenous melatonin. These results demonstrate that memory related activation in the hippocampus and para-hippocampus are affected by time of day and melatonin in a differential manner and may implicate the circadian clock and melatonin in human memory processing during the night.

Long-term study of dendritic spines from hippocampal CA1 pyramidal cells, after neuroprotective melatonin treatment following global cerebral ischemia in rats

Melatonin reduces pyramidal neuronal death in the hippocampus and prevents the impairment of place learning and memory in the Morris water maze, otherwise occurring following global cerebral ischemia. The cytoarchitectonic characteristics of the hippocampal CA1 remaining pyramidal neurons in brains of rats submitted 120 days earlier to acute global cerebral ischemia (15-min four vessel occlusion, and melatonin 10mg/(kg h 6h), i.v. or vehicle administration) were compared to those of intact control rats in order to gain information concerning the neural substrate underlying preservation of hippocampal functioning. Hippocampi were processed according to a modification of the Golgi method. Dendritic bifurcations from pyramidal neurons in both the oriens-alveus and the striatum radiatum; as well as spine density and proportions of thin, stubby, mushroom-shaped, wide, ramified, and double spines in a 50 microm length segment of an oblique dendrite branching from the apical dendrite of the hippocampal CA1 remaining pyramidal neurons were evaluated. No impregnated CA1 pyramidal neurons were found in the ischemic-vehicle-treated rats. CA1 pyramidal neurons from ischemic-melatonin-treated rats showed stick-like and less ramified dendrites than those seen in intact control neurons. In addition, lesser density of spines, lower proportional density of thin spines, and higher proportional density of mushroom spines were counted in ischemic-melatonin-treated animals than those in the sinuously branched dendrites of the intact control group. These cytoarchitectural arrangements seem to be compatible with place learning and memory functions long after ischemia and melatonin neuroprotection.