Intermediate-term memory is modulated by the circadian clock.

Sensitization of the tail-siphon withdrawal reflex in Aplysia, a non-associative form of learning, affords a superb opportunity to investigate the regulation of learning and memory by the circadian clock. The circadian clock has been shown to modulate long-term (LTS), but not short-term sensitization (STS). However, no previous studies have examined the role of the circadian clock in intermediate-term memory. Noxious stimulation delivered to the side of the animal using a spaced training protocol resulted in canonical intermediate-term sensitization (ITS) dependent upon both MAPK signaling and protein synthesis. We found that ITS exhibited strong rhythms in expression in both light-dark cycles and constant darkness. Animals trained during the (subjective) day demonstrated significantly more intermediate-term memory than animals trained at night. Baseline responses prior to training were not modulated by the circadian clock. Thus, these results indicate that the circadian clock strongly modulates intermediate, as well as long-term memory.

海兔的尾部虹吸管收缩反射敏化是一种非联想式学习形式，为研究生物钟对学习和记忆的调节提供了绝佳机会。生物钟已被证明可调节长期敏化（LTS），但不调节短期敏化（STS）。然而，之前没有研究探讨过生物钟在中期记忆中的作用。使用间隔训练方案对动物体侧进行有害刺激，会导致典型的中期敏化（ITS），这依赖于丝裂原活化蛋白激酶（MAPK）信号传导和蛋白质合成。我们发现，在光暗周期和恒暗条件下，ITS的表达都呈现出强烈的节律。在（主观）白天接受训练的动物比在夜间接受训练的动物表现出明显更强的中期记忆。训练前的基线反应不受生物钟调节。因此，这些结果表明生物钟对中期以及长期记忆都有强烈的调节作用。