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Abstract
Melatonin is the main hormone of the pineal gland that informs the body about the environmental light and darkness regimen and is considered to regulate many important physiological and behavioural activities. In the present study, we examined the effects of pinealectomy, constant-release melatonin implants and timed melatonin injections on spatial memory in male Wistar rats by using Morris water maze. Pinealectomy, melatonin injection and melatonin implantation were performed on groups, including controls for all groups. After a week of the pinealectomy and melatonin implantation surgeries, we applied the injections and made the training trials throughout 4 days. At the fifth day, experiments were performed and recorded. Spatial memory performance of the rats was impaired by the pinealectomy and melatonin injections, since they elongated the latency and shortened the time passed in the correct quadrant. Melatonin implantation did not affect the spatial memory performance of the rats. The latency and the time passed in correct quadrant were not statistically different from their controls. The results suggest that while the removal of the pineal gland and exogenous administration of melatonin via injections are causing impairment, constant-release melatonin administration via implantation does not affect the spatial memory in Wistar albino rats.