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

Melatonin Improves Oxidative Stress Injury in Retinopathy of Prematurity by Targeting miR-23a-3p/Nrf2

PURPOSE

Melatonin has promising protective effects for retinopathy. However, its roles in retinopathy of prematurity (ROP) and the underlying mechanisms remain unknown. We aimed to explore its roles and mechanisms in a ROP model.

METHODS

Hematoxylin and eosin staining were used to observe the morphology of the retina. Immunofluorescence was used to detect positive (Nrf2+ and VEGF+) cells. Immunohistochemistry was used to detect the level of nuclear expression of PCNA in retinal tissue. Transmission electron microscope (TEM) was used to observe the morphology and structure of pigment cells. qRT-PCR was used to assay the expression of miR-23a-3p, Nrf2, and HO-1. Western blotting was used to detect the expression of Nrf2, HO-1, β-actin, and Lamin B1.

RESULTS

Melatonin or miR-23a-3p antagomir treatment could ameliorate the Oxygen-induced pathological changes, increased the expression of Nrf2 and HO-1, SOD, and GSH-Px, and decreased the expression of VEGF, miR-23a-3p, MDA and the apoptosis in the ROP model. Further target prediction and luciferase reporter assays confirmed the targeted binding relationship between miR-23a-3p and Nrf2.

CONCLUSION

Our study showed that melatonin could ameliorate H2O2-induced apoptosis and oxidative stress injury in RGC cells by mediating miR-23a-3p/Nrf2 signaling pathway, thereby improving retinal degeneration.

Design, synthesis, molecular docking and DFT studies on novel melatonin and isatin based azole derivatives

In order to address the pressing demand for newer broad-spectrum antifungal medicines with enhanced activity, computer modelling was utilised to rationally develop newer antifungal azole-based drugs. Based on the drug and active sites of the Lanosterol 14 alpha-Demethylases (LAD) of the prominent fungal pathogen Candida albicans interaction, Novel triazole-linked melatonin and isatin derivatives 7a-d and 8a-d were synthesised using bioisosterism. Besides the experimental synthesis and subsequent characterization, the present study focused on obtaining optimised geometries, frequency calculations, and TD-DFT studies of the synthesised molecules. We also performed molecular docking studies to explore the inhibitory ability of the synthesised compounds against the active sites of the Lanosterol 14 alpha-Demethylases (LAD) of the prominent fungal pathogen Candida albicans. The binding interactions resulted in positive findings, demonstrating the involvement of the synthesised compounds in the suppression of fungal growth. Comparative analysis of the binding potential of the synthesised molecules and commercially available drug fluconazole revealed a remarkable note: the docking scores for the designed drugs 7b, 7c, and 8c are much greater than those of the fluconazole molecule. The in silico study of the designed series of drug molecules serves as an important guideline for further exploration in the quest for potent antifungal agents.

Neuroendocrine regulation in stroke

The neuroendocrine system, a crosstalk between the central nervous system and endocrine glands, balances and controls hormone secretion and their functions. Neuroendocrine pathways and mechanisms often get dysregulated following stroke, leading to altered hormone secretion and aberrant receptor expression. Dysregulation of the hypothalamus-pituitary-thyroid (HPT) axis and hypothalamus-pituitary-adrenal (HPA) axis often led to severe stroke outcomes. Post-stroke complications such as cognitive impairment, depression, infection etc. are directly or indirectly influenced by the altered neuroendocrine activity that plays a crucial role in stroke vulnerability and susceptibility. Therefore, it is imperative to explore various neurohormonal inter-relationships in regulating stroke, its outcome, and prognosis. Here, we review the biology of different hormones associated with stroke and explore their regulation with a view towards prospective therapeutics.

Neuro-Inflammation Modulation and Post-Traumatic Brain Injury Lesions: From Bench to Bed-Side

Head trauma is the most common cause of disability in young adults. Known as a silent epidemic, it can cause a mosaic of symptoms, whether neurological (sensory-motor deficits), psychiatric (depressive and anxiety symptoms), or somatic (vertigo, tinnitus, phosphenes). Furthermore, cranial trauma (CT) in children presents several particularities in terms of epidemiology, mechanism, and physiopathology-notably linked to the attack of an immature organ. As in adults, head trauma in children can have lifelong repercussions and can cause social and family isolation, difficulties at school, and, later, socio-professional adversity. Improving management of the pre-hospital and rehabilitation course of these patients reduces secondary morbidity and mortality, but often not without long-term disability. One hypothesized contributor to this process is chronic neuroinflammation, which could accompany primary lesions and facilitate their development into tertiary lesions. Neuroinflammation is a complex process involving different actors such as glial cells (astrocytes, microglia, oligodendrocytes), the permeability of the blood-brain barrier, excitotoxicity, production of oxygen derivatives, cytokine release, tissue damage, and neuronal death. Several studies have investigated the effect of various treatments on the neuroinflammatory response in traumatic brain injury in vitro and in animal and human models. The aim of this review is to examine the various anti-inflammatory therapies that have been implemented.

Delirium REduction after administration of melatonin in acute ischemic stroke (DREAMS): A propensity score-matched analysis

BACKGROUND AND PURPOSE

Poststroke delirium (PSD) comprises a common and severe complication after stroke. However, treatment options for PSD remain insufficient. We investigated whether prophylactic melatonin supplementation may be associated with reduced risk for PSD.

METHODS

Consecutive patients admitted to the Tübingen University Stroke Unit, Tübingen, Germany, with acute ischemic stroke (AIS), who underwent standard care between August 2017 and December 2017, and patients who additionally received prophylactic melatonin (2 mg per day at night) within 24 h of symptom onset between August 2018 and December 2018 were included. Primary outcomes were (i) PSD prevalence in AIS patients and (ii) PSD risk and PSD-free survival in patients with cerebral infarction who underwent melatonin supplementation compared to propensity score-matched (PSM) controls. Secondary outcomes included time of PSD onset and PSD duration.

RESULTS

Out of 465 (81.2%) patients with cerebral infarction and 108 (18.8%) transient ischemic attack (TIA) patients, 152 (26.5%) developed PSD (median time to onset [IQR]: 16 [8-32] h; duration 24 [8-40] h). Higher age, cerebral infarction rather than TIA, and higher National Institutes of Health Stroke Scale score and aphasia on admission were significant predictors of PSD. After PSM (164 melatonin-treated patients with cerebral infarction versus 164 matched controls), 42 (25.6%) melatonin-treated patients developed PSD versus 60 (36.6%) controls (odds ratio, 0.597; 95% confidence interval, 0.372-0.958; p = 0.032). PSD-free survival differed significantly between groups (p = 0.027), favoring melatonin-treated patients. In patients with PSD, no between-group differences in the time of PSD onset and PSD duration were noted.

CONCLUSIONS

Patients prophylactically treated with melatonin within 24 h of AIS onset had lower risk for PSD than patients undergoing standard care. Prospective randomized trials are warranted to corroborate these findings.

Role of Melatonin on Virus-Induced Neuropathogenesis-A Concomitant Therapeutic Strategy to Understand SARS-CoV-2 Infection

Viral infections may cause neurological disorders by directly inducing oxidative stress and interrupting immune system function, both of which contribute to neuronal death. Several reports have described the neurological manifestations in Covid-19 patients where, in severe cases of the infection, brain inflammation and encephalitis are common. Recently, extensive research-based studies have revealed and acknowledged the clinical and preventive roles of melatonin in some viral diseases. Melatonin has been shown to have antiviral properties against several viral infections which are accompanied by neurological symptoms. The beneficial properties of melatonin relate to its properties as a potent antioxidant, anti-inflammatory, and immunoregulatory molecule and its neuroprotective effects. In this review, what is known about the therapeutic role of melatonin in virus-induced neuropathogenesis is summarized and discussed.

Therapeutic potential of melatonin as a chronobiotic and cytoprotective agent in diabetes mellitus

PURPOSE

Diabetes mellitus is a complex metabolic disorder characterized by hyperglycemia occurring as a result of dysregulation and balance of various metabolic pathways. In recent years, circadian misalignment (due to altered sleep/wake, feeding/fasting cycles), has been intimately linked with the development of diabetes mellitus. Herein, we review our knowledge of oxidative stress, circadian rhythms control of metabolism, and the effects of its disruption on homeostasis while emphasizing the importance of melatonin, a nocturnally peaking, pineal hormone, as a potential therapeutic drug for the prevention and treatment of diabetes.

METHODS

PubMed database was systematically searched for related articles and data from all types of studies, including clinical trials, review articles, and case reports were considered without limiting the study to one specific category.

RESULTS

Experimental and epidemiological evidence indicate melatonin's multifaceted effects in intermediary metabolism via resynchronization of the circadian rhythms and its deficiency is associated with metabolic derangements. As a chronobiotic, it cures insomnia and sleep disorders caused by shift work or jet lag. The antagonistic relationship between melatonin and insulin highlights its influence in regulating insulin secretion, its action, and melatonin treatment successfully improved glucose homeostasis, energy balance, and overall health in diabetes mellitus. Melatonin's cytoprotective role as an antioxidant and free radical scavenger, proved useful in combating oxidative stress, preserving beta-cell function, and influencing the development of diabetic complications.

CONCLUSION

The therapeutic application of melatonin as a chronobiotic and cytoprotective agent is of promising significance in diabetes mellitus. Future investigations are encouraged to fully explore the efficacy of this ubiquitous molecule in various metabolic disorders.

Melatonin-A Potent Therapeutic for Stroke and Stroke-Related Dementia

Secreted by the pineal gland to regulate the circadian rhythm, melatonin is a powerful antioxidant that has been used to combat oxidative stress in the central nervous system. Melatonin-based therapies have been shown to provide neuroprotective effects in the setting of ischemic stroke by mitigating neuroinflammation and accelerating brain tissue restoration. Melatonin treatment includes injection of exogenous melatonin, pineal gland grafting and melatonin-mediated stem cell therapy. This review will discuss the current preclinical and clinical studies investigating melatonin-based therapeutics to treat stroke.

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.

Melatonin attenuated the brain damage and cognitive impairment partially through MT2 melatonin receptor in mice with chronic cerebral hypoperfusion

Background

Vascular cognitive impairment (VCI) is a spectrum of cognitive impairment caused by various chronic diseases including aging, hypertension, and diabetes mellitus. Oxidative and inflammatory reactions induced by chronic cerebral hypoperfusion (CHP) are believed to cause VCI. Melatonin is reported to possess anti-oxidation and anti-inflammation effects. This study was designed to investigate the effect and mechanisms of melatonin in CHP mice model.

Results

The behavioral function results revealed that CHP mice were significantly impaired when compared with the control. Melatonin improved the cognitive function, but the addition of MT2 receptor antagonist reversed the improvement. The IHC staining showed melatonin significantly improved WM lesions and gliosis in CHP mice. Again, the addition of MT2 receptor antagonist to melatonin worsened the WM lesion and gliosis. Similar results were also found for mRNA and protein expressions of oxidative reaction and inflammatory cytokines.

Materials and Method

Forty C57BL/6 mice were divided into four groups: Group 1: sham control; Group 2: CHP mice; Group 3: CHP with melatonin treatment; Group 4: CHP-melatonin and MT2 receptor antagonist (all groups n = 10). Working memory was assessed with Y–arm test at day-28 post-BCAS (bilateral carotid artery stenosis). All mice were sacrificed at day-30 post-BCAS. The immunohistochemical (IHC) staining was used for white matter (WM) damage and gliosis. The expression of mRNA and proteins about inflammatory and oxidative reaction were measured and compared between groups.

Conclusions

Partially through MT2 receptor, melatonin is effective for CHP-induced brain damage.

Melatonin as an Antioxidant for Stroke Neuroprotection

Melatonin (N-acetyl-5-methoxytryptamine) is a hormone derived from the pineal gland that has a wide range of clinical applications. While melatonin was originally assessed as a hormone specializing in regulation of the normal circadian rhythm in mammals, it now has been shown to be an effective free radical scavenger and antioxidant. Current research has focused on central nervous system (CNS) disorders, stroke in particular, for potential melatonin-based therapeutics. As of now, the realm of potential therapy regimens is focused on three main treatments: exogenously delivered melatonin, pineal gland grafting, and melatonin-mediated stem cell therapy. All therapies contain both costs and benefits, and current research is still focused on finding the best treatment plan. While comprehensive research has been conducted, more research regarding the safety of such therapies is needed in order to transition into the clinical level of testing. Antioxidants such as traditional Chinese medicine, (-)-epigallocatechin-3-gallate (EGCG), and lavender oil, which have been used for thousands of years as treatment, are now gaining recognition as effective melatonin treatment alternatives. This review will further discuss relevant studies assessing melatonin-based therapeutics and provide evidence of other natural melatonin treatment alternatives for the treatment of stroke.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Effects of pretreatment with a combination of melatonin and electroacupuncture in a rat model of transient focal cerebral ischemia

Both melatonin and electroacupuncture (EA) have been suggested to be effective treatments against stroke. However, it is unknown whether a combination of these two therapies could be beneficial against transient focal cerebral ischemia. The present study investigated the effects of pretreatment of a combination of melatonin and EA in a rat model of transient middle cerebral artery occlusion (MCAO). After pretreatment of melatonin plus EA (MEA), transient MCAO was induced for 90 minutes in male Sprague-Dawley (SD) rats. The neurological deficit score, brain infarct volume, cerebral edema ratio, neuronal inflammation, and apoptosis were evaluated 24 hours after transient MCAO. The expression of related inflammatory and apoptotic mediators in the brain was also investigated. The results showed that MEA improved neurological outcome, reduced brain infarct volume, and inhibited neuronal inflammation as well as apoptosis 24 hours after transient MCAO. The beneficial effects may derive from downregulation of proinflammatory and proapoptotic mediators and upregulation of antiapoptotic mediators. Thus, these results suggest a preventive effect of pretreatment of MEA on transient focal cerebral ischemia.

Melatonin-based therapeutics for neuroprotection in stroke

The present review paper supports the approach to deliver melatonin and to target melatonin receptors for neuroprotection in stroke. We discuss laboratory evidence demonstrating neuroprotective effects of exogenous melatonin treatment and transplantation of melatonin-secreting cells in stroke. In addition, we describe a novel mechanism of action underlying the therapeutic benefits of stem cell therapy in stroke, implicating the role of melatonin receptors. As we envision the clinical entry of melatonin-based therapeutics, we discuss translational experiments that warrant consideration to reveal an optimal melatonin treatment strategy that is safe and effective for human application.

Dynamics of oxidative stress and urinary excretion of melatonin and its metabolites during acute ischemic stroke

Oxidative stress is a leading cause of neuronal damage in ischemic stroke. Melatonin may play a role in the antioxidant response. Melatonin and its metabolites may be involved in the modulation of oxidative stress in human acute stroke. No data are available in humans to establish this relationship. In this context, on the first and the fifth days post-stroke, we assessed serum total antioxidant capacity (TAC) and urine levels of melatonin, 6-sulfatoxymelatonin (aMT6S), and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), the last compound being produced in the brain after reaction of melatonin with reactive oxygen species. Compared to controls' values, TAC and levels of melatonin and aMT6S were reduced, without difference between the first and the fifth days post-stroke, whereas AFMK levels remained in the normal range at both time points. Melatonin catabolism might be speeded up in acute ischemic stroke in order to increase the antioxidant response.

Melatonin ameliorates neural function by promoting endogenous neurogenesis through the MT2 melatonin receptor in ischemic-stroke mice

Melatonin has many protective effects against ischemic stroke, but the underlying neuroprotective mechanisms are not fully understood. Our aim was to explore the relationship between melatonin's neuroprotective effects and activation of the MT2 melatonin receptor in a murine ischemic-stroke model. Male ICR mice were subjected to a transient middle cerebral ischemic/reperfusional injury, and melatonin (5 and 10 mg/kg, ip) was administrated once daily starting 2 h after ischemia. More than 80% of the mice died within 5 days after stroke without treatment. Melatonin treatment significantly improved the survival rates and neural functioning with modestly prolonged life span of the stroke mice by preserving blood-brain barrier (BBB) integrity via a reduction in the enormous amount of stroke-induced free radical production and significant gp91(phox) cell infiltration. These protective effects of melatonin were reversed by pretreatment with MT2 melatonin receptor antagonists (4-phenyl-2-propionamidotetralin (4P-PDOT) and luzindole). Moreover, treatment with melatonin after stroke dramatically enhanced endogenous neurogenesis (doublecortin positive) and cell proliferation (ki67 positive) in the peri-infarct regions. Most ki67-positive cells were nestin-positive and NG2-positive neural stem/progenitor cells that coexpressed two neurodevelopmental proteins (adam11 and adamts20) and the MT2 melatonin receptor. RT-PCR revealed that the gene expression levels of doublecortin, ki67, adamts20, and adam11 are markedly reduced by stroke, but are restored by melatonin treatment; furthermore, pretreatment with 4P-PDOT and luzindole antagonized melatonin's restorative effect. Our results support the hypothesis that melatonin is able to protect mice against stroke by activating MT2 melatonin receptors, which reduces oxidative/inflammatory stress. This results in the preservation of BBB integrity and enhances endogenous neurogenesis by upregulating neurodevelopmental gene/protein expression.

Human amniotic epithelial cells express melatonin receptor MT1, but not melatonin receptor MT2: a new perspective to neuroprotection

Recent studies have demonstrated that the human placenta is a novel source of adult stem cells. We have provided laboratory evidence that transplantation of these human placenta-derived cells in vitro and in vivo stroke models promotes functional recovery. However, the mechanisms underlying these observed therapeutic benefits of human placenta-derived cells unfortunately remain poorly understood. Here, we examined the expression of two discrete types of melatonin receptors and their roles in proliferation and differentiation of cultured human amniotic epithelial cells (AECs). Cultured AECs express melatonin receptor type 1A (MT1), but not melatonin receptor type 1B (MT2). The proliferation of cultured AECs was increased in the melatonin-treated group in a dose-dependent manner, and the viability of cultured AECs could be further enhanced by melatonin. Moreover, the viability of AECs significantly decreased with H(2) O(2) exposure, which was reversed by pretreatment with melatonin, resulting in increased cell survival rate and cell proliferation. Immunocytochemically, administration of melatonin significantly suppressed nestin proliferation, but enhanced TUJ1 differentiation of MT1-expressing AECs. Additional experiments incorporating antibody blocking and synergistic AEC-melatonin treatments further showed AEC therapeutic benefits via MT1 modulation. Finally, analysis of trophic factors revealed cultured AECs secreted VEGF in the presence of melatonin. These data indicate that melatonin by stimulating MT1 increased cell proliferation and survival rate while enhancing neuronal differentiation of cultured AECs, which together with VEGF upregulation, rendered neuroprotection against experimental in vitro models of ischemic and oxidative stress injury.

Melatonin inhibits postischemic matrix metalloproteinase-9 (MMP-9) activation via dual modulation of plasminogen/plasmin system and endogenous MMP inhibitor in mice subjected to transient focal cerebral ischemia

We have shown that melatonin attenuated matrix metalloproteinase-9 (MMP-9) activation and decreased the risk of hemorrhagic transformation following cerebral ischemia-reperfusion. Herein, we investigate the possible involvement of the plasminogen/plasmin system and endogenous MMPs inhibitor underlying the melatonin-mediated MMP-9 inhibition. Mice were subjected to 1-hr ischemia and 48-hr reperfusion of the right middle cerebral artery. Melatonin (5 mg/kg) or vehicle was intravenously injected upon reperfusion. Brain infarction and hemorrhagic transformation were measured. Extracellular matrix damage was determined by Western immunoblot analysis for laminin protein. The activity and expression of MMP-2 and MMP-9 were determined by gelatin zymography, in situ zymography, and Western immunoblot analysis. In addition, the activities of tissue and urokinase plasminogen activators (tPA and uPA) were evaluated by plasminogen-dependent casein zymography. Endogenous plasminogen activator inhibitor (PAI) and tissue inhibitors of MMP (TIMP-1) were investigated using enzyme-linked immunosorbent assay (ELISA) and Western immunoblot analysis, respectively. Cerebral ischemia-reperfusion induced increased MMP-9 activity and expression at 12-48 hr after reperfusion onset. Relative to controls, melatonin-treated animals had significantly decreased MMP-9 activity and expression (P<0.05), in addition to reduced brain infarction and hemorrhagic transformation as well as improved laminin protein preservation. This melatonin-mediated MMP-9 inhibition was accompanied by reduced uPA activity (P<0.05), as well as increased TIMP-1 expression and PAI activity (P<0.05, respectively). These results demonstrate the melatonin's pluripotent mechanisms for attenuating postischemic MMP-9 activation and neurovascular damage, and further support it as an add-on to thrombolytic therapy for ischemic stroke patients.

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.