Objective: 

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenous indoleamine secreted by the pineal gland especially in response to darkness. It has many functions including acting as an antioxidant and assisting to regulate circadian rhythms. Furthermore, it has been recently reported that melatonin may affect on learning and memory in mice, and it can modify electrophysiological procedures associated with memory. The aim of the present study was to analyze the effects of pinealectomy and exogenous melatonin administration on passive avoidance response in adult male Sprague Dawley rats.

Methods: 

Animals were separated into six groups (n=8) as control, 5% ethanol, sham-operated, melatonin, pinealectomy, pinealectomy+melatonin groups. The two groups of rats were exposed to pinealectomy, and seven days after surgery, animals in the melatonin and pinealectomy+melatonin groups were administrated daily with melatonin (10 mg/kg i.p.) for 14 days. Cognitive functions were assessed using step-through latency on the passive avoidance apparatus.

Results: 

As a result of the statistical analysis of the obtained data, pinealectomy and exogenous melatonin administration was not any effect on the passive avoidance learning in rats. In addition, there was no significant difference in the avoidance latency in sham, ethanol and pinealectomy + melatonin groups compared to the control group.

Conclusions: 

In conclusion, we suggest that melatonin does not act directly on the learning of passive avoidance behavior in rats.