Interaction of visual experience and melatonin in the spatial task learning

During a postnatal critical period, sensory experience modifications cause changes in electrophysiological and behavioral considerations. Pineal melatonin secretion follows a circadian rhythm, rising during darkness and waning by light. This study evaluated interaction of visual signals and melatonin on spatial performance of animals reared on 12 light/dark cycle (control; CO), constant light (light reared; LR) and total darkness (dark reared; DR). Each group was administered vehicle and/or melatonin (5 mg/kg) intraperitonealy. The animals were introduced to a water maze task 4 trials/day for 5 days. The time spent and distance traveled to find the platform were measured. We found a superiority of the CO rats on both LR and DR groups. Melatonin impaired the task learning in the CO animals. Conversely, the LR and DR animals were insensitive to melatonin. Conclusively, visual experience modifications, whether light or dark deprivation, impaired the spatial learning. Also, exogenous melatonin influenced behavior of only normally reared animals.