Melatonin Improves Neuroprotection and Neuroplasticity in Middle-Aged Mice Following Permanent Focal Cerebral Ischemia.

Stroke, caused by interrupted brain blood supply, predominantly affects the elderly. Epidemiological data indicate that over 70% of ischemic strokes occur in individuals aged 65 and above, and older patients are more likely to experience worse functional recovery and higher mortality rates. Most models use young animals, limiting clinical relevance for aged patients. Studying aged animals is more clinically applicable, especially since older patients often experience severe strokes. We selected a permanent middle cerebral artery occlusion (pMCAO) model to reflect strokes where reperfusion therapy is not achieved. A significant proportion of stroke patients (particularly older individuals) do not receive or benefit from thrombolysis/thrombectomy, leaving them with permanent arterial occlusion. In our aged mice model, pMCAO provides a stringent test of neuroprotective efficacy under conditions of sustained ischemia, which can illuminate melatonin's potential benefits in severe, unmanaged stroke. Melatonin, a potent antioxidant, has been shown to reduce infarction volume and improve neurobehavioral and electrophysiological recovery in ischemic stroke models. In this study, our objective was to assess the neuroprotective and neuroplasticity effects of melatonin as reflected by dendritic spine density and arborization in middle-aged mice (12-13 months old), a relevant model for aging-related stroke pathology. In this study, "middle-aged" refers to 12-13-month-old ICR mice, equivalent to approximately 40-50 human years. Twelve-month old male ICR mice subjected to pMCAO were treated with melatonin (5 mg/kg) or a vehicle before undergoing surgery. Neurobehavioral performance was assessed 24 h post-surgery, and brain tissues were collected for Golgi-Cox staining to assess stroke-induced neuronal dendritic damage and neuroplasticity. Melatonin treatment notably decreased infarct volume and neuronal degeneration, while enhancing neuron survival, increasing dendritic spine density, and promoting functional neuroplasticity in ischemic regions and promoting better neurobehavioral recovery compared to the vehicle controls (P < 0.05). In addition to evaluating infarct volume and synaptic plasticity, we assessed lipofuscin accumulation as a histological marker of neuronal aging and oxidative stress. Melatonin treatment reduced lipofuscin deposits, suggesting a potential role in attenuating age-related neurodegeneration. The administration of melatonin also resulted in a significant increase in dendritic spine density (P < 0.05) within the second- and third-order basilar dendrites of pyramidal neurons in layers II-III and III-IV of the penumbra, as well as in layer V-VI of both the ipsilateral (ischemic) and contralateral (nonischemic) cortex, when compared to vehicle controls (P < 0.05). In addition, melatonin treatment enhanced dendritic arborization in pyramidal neurons within layers II-III and III-IV of the ipsilateral cortex (P < 0.05). Furthermore, melatonin upregulation brain-derived neurotrophic factor (BDNF), growth-associated protein 43 (GAP-43) and synaptosomal-associated protein 25 (SNAP-25) expression post-insults. In this study, melatonin showed significant neuroprotective effects after ischemic stroke and enhanced neuroplasticity in middle-aged mice, suggesting its potential application in aging-related stroke therapy.