Melatonin Rescue Oxidative Stress-Mediated Neuroinflammation/ Neurodegeneration and Memory Impairment in Scopolamine-Induced Amnesia Mice Model.

Cognitive decline and memory impairment induced by oxidative brain damage are the critical pathological hallmarks of Alzheimer's disease (AD). Based on the potential neuroprotective effects of melatonin, we here explored the possible underlying mechanisms of the protective effect of melatonin against scopolamine-induced oxidative stress-mediated c-Jun N-terminal kinase (JNK) activation, which ultimately results in synaptic dysfunction, neuroinflammation, and neurodegeneration. According to our findings, scopolamine administration resulted in LPO and ROS generation and decreased the protein levels of antioxidant proteins such as Nrf2 and HO-1; however, melatonin co-treatment mitigated the generation of oxidant factors while improving antioxidant protein levels. Similarly, melatonin ameliorated oxidative stress-mediated JNK activation, enhanced Akt/ERK/CREB signaling, promoted cell survival and proliferation, and promoted memory processes. Immunofluorescence and western blot analysis indicated that melatonin reduced activated gliosis via attenuation of Iba-1 and GFAP. We also found that scopolamine promoted neuronal loss by inducing Bax, Pro-Caspase-3, and Caspase-3 and reducing the levels of the antiapoptotic protein Bcl-2. In contrast, melatonin significantly decreased the levels of apoptotic markers and increased neuronal survival. We further found that scopolamine disrupted synaptic integrity and, conversely, that melatonin enhanced synaptic integrity as indicated by Syntaxin, PSD-95, and SNAP-23 expression levels. Furthermore, melatonin ameliorated scopolamine-induced impairments in spatial learning behavior and memory formation. On the whole, our findings revealed that melatonin attenuated scopolamine-induced synaptic dysfunction and memory impairments by ameliorating oxidative brain damage, stress kinase expression, neuroinflammation, and neurodegeneration. Graphical Abstract The proposed schematic diagram showing the neuroprotective effect of melatonin against scopolamine-induced oxidative stress-mediated synaptic dysfunction, memory impairment neuroinflammation and neurodegeneration.