Major role of MT2 receptors in the beneficial effect of melatonin on long-term recognition memory in C57BL/6J male mice.

Melatonin, a major signal of the circadian system, is also involved in brain functions such as learning and memory. Chronic melatonin treatment is known to improve memory performances, but the respective contribution of its central receptors, MT1 and MT2, is still unclear. Here, we used new single receptor deficient MT1-/- and MT2-/- mice to investigate the contribution of each receptor in the positive effect of chronic melatonin treatment on long-term recognition memory. The lack of MT2 receptor precluded memory-enhancing effect of melatonin in the object recognition task and to a lesser extent in the object location task, whereas the lack of MT1 receptor mitigated its effect in the object location task only. Our findings support a key role of MT2 in mediating melatonin's beneficial action on long-term object recognition memory, whereas MT1 may contribute to the effect on object location memory.