Research reportThe effects of the intraamygdalar melatonin injections on the anxiety like behavior and the spatial memory performance in male Wistar rats

In the present study, the effects of intraamygdalar administrations of melatonin (1 and 100 μg/kg), saline and diazepam on the anxiety-like behavior and spatial memory performance in pinealectomized and sham-pinealectomized Wistar rats were investigated. The animals were tested by open field and elevated plus maze tests for anxiety-like behavior, and Morris water maze test for spatial memory. In open field, (a) diazepam was more effective in reducing the anxiety, (b) control subjects were more mobile than pinealectomized subjects and (c) 100 μg/kg melatonin administrations reduced the velocity of the animals. In elevated plus maze, (a) 100 μg/kg melatonin administrations increased the distance totally travelled and (b) enhanced the time spent in open arms, however, after the pinealectomy, 1 μg/kg melatonin administrations decreased it and (c) control animals were less mobile than pinealectomized ones. In Morris water maze, (a) diazepam group travelled more distance than the others in control condition whereas, in pinealectomy condition high dose of melatonin and saline groups travelled more distance than the others, (b) in pinealectomy condition subjects who received 100 μg/kg melatonin also travelled more distance than those who received 1 μg/kg melatonin and diazepam, (c) the subjects who received 1 μg/kg spent less time than those who received other treatments, and (d) in control condition subjects who received 100 μg/kg melatonin were slower than those who received the other treatments. In conclusion, melatonin administration to amygdala decreased the anxiety; however, spatial memory performance of the rats was impaired by the pinealectomy and melatonin administrations.

► Melatonin has anxiolytic and some therapeutic effects on the learning disorders. ► The amygdala regulate the behaviours related to the anxiety and memory. ► Intraamygdalar administrations of melatonin was tested on the anxiety and memory. ► Melatonin administration to amygdala decreased the anxiety. ► Spatial memory performance was impaired by the pinealectomy and the melatonin.