Melatonin is a Neuroprotective and Antioxidant Agent against Neurotoxicity Induced by an Intrahippocampal Injection of Nickel in Rats

The investigation into the hippocampal function and its response to heavy metal exposure is crucial for understanding the mechanisms underlying neurotoxicity, this can potentially inform strategies for mitigating the adverse effects associated with heavy metal exposure. Melatonin is an essential neuromodulator known for its efficacy as an antioxidant. In this study, we aimed to determine whether melatonin could protect against Nickel (Ni) neurotoxicity. To achieve this, we performed an intracerebral injection of Ni (300 µM NiCl₂) into the right hippocampus of male Wistar rats, followed by melatonin treatment. Based on neurobehavioral and neurobiochemical assessments, our results demonstrate that melatonin efficiently enhances Ni-induced behavioral dysfunction and cognitive impairment. Specifically, melatonin treatment positively influences anxious behavior, significantly reduces immobility time in the forced swim test (FST), and improves learning and spatial memory abilities. Moreover, neurobiochemical assays revealed that melatonin treatment modulates the Ni-induced alterations in oxidative stress balance by increasing antioxidant enzyme activities, such as superoxide dismutase (SOD) and catalase (CAT). Additionally, we observed that melatonin significantly attenuated the increased levels of lipid peroxidation (LPO) and nitric oxide (NO). In conclusion, the data from this study suggests that melatonin attenuates oxidative stress, which is the primary mechanism responsible for Ni-induced neurotoxicity. Considering that the hippocampus is the main structure involved in the pathology associated with heavy metal intoxication, such as Ni, these findings underscore the potential therapeutic efficacy of melatonin in mitigating heavy metal-induced brain damage.